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The mechanisms whereby orofacial pain affects motor function are poorly understood. The aims were to determine whether 1) lingual algesic chemical stimulation affected face primary motor cerebral cortex (face MI) excitability defined by intracortical microstimulation (ICMS); and 2) any such effects were limited to the motor efferent MI zones driving muscles in the vicinity of the noxious stimulus. Ketamine-anesthetized Sprague–Dawley male rats were implanted with electromyographic (EMG) electrodes into anterior digastric, masseter, and genioglossus muscles. In 38 rats, three microelectrodes were located in left face MI at ICMS-defined sites for evoking digastric and/or genioglossus responses. ICMS thresholds for evoking EMG activity from each site were determined every 15 min for 1 h, then the right anterior tongue was infused (20 µl, 120 µl/h) with glutamate (1.0 M, n = 18) or isotonic saline (n = 7). Subsequently, ICMS thresholds were determined every 15 min for 4 h. In intact control rats (n = 13), ICMS thresholds were recorded over 5 h. Only left and right genioglossus ICMS thresholds were significantly increased (≤350%) in the glutamate infusion group compared with intact and isotonic saline groups (P < 0.05). These dramatic effects of glutamate on ICMS-evoked genioglossus activity contrast with its weak effects only on right genioglossus activity evoked from the internal capsule or hypoglossal nucleus. This is the first documentation that intraoral noxious stimulation results in prolonged neuroplastic changes manifested as a decrease in face MI excitability. These changes appear to occur predominantly in those parts of face MI that provide motor output to the orofacial region receiving the noxious stimulation. [ABSTRACT FROM AUTHOR]

It is well established that permanent or transient reduction of somatosensory inputs, following hand deafferentation or anesthesia, induces plastic changes across the hand-face border, supposedly responsible for some altered perceptual phenomena such as tactile sensations being referred from the face to the phantom hand. It is also known that transient increase of hand somatosensory inputs, via repetitive somatosensory stimulation (RSS) at a fingertip, induces local somatosensory discriminative improvement accompanied by cortical representational changes in the primary somatosensory cortex (SI). We recently demonstrated that RSS at the tip of the right index finger induces similar training-independent perceptual learning across the hand-face border, improving somatosensory perception at the lips (Muret D, Dinse HR, Macchione S, Urquizar C, Farnè A, Reilly KT.Curr Biol24: R736-R737, 2014). Whether neural plastic changes across the hand-face border accompany such remote and adaptive perceptual plasticity remains unknown. Here we used magnetoencephalography to investigate the electrophysiological correlates underlying RSS-induced behavioral changes across the hand-face border. The results highlight significant changes in dipole location after RSS both for the stimulated finger and for the lips. These findings reveal plastic changes that cross the hand-face border after an increase, instead of a decrease, in somatosensory inputs., (Copyright © 2016 the American Physiological Society.)

Rodents use their vibrissae to detect and discriminate tactile features during active exploration. The site of mechanical transduction in the vibrissa sensorimotor system is the follicle sinus complex and its associated vibrissa. We study the mechanics within the ring sinus (RS) of the follicle in an ex vivo preparation of the mouse mystacial pad. The sinus region has a relatively dense representation of Merkel mechanoreceptors and longitudinal lanceolate endings. Two-photon laser-scanning microscopy was used to visualize labeled cell nuclei in an ∼ 100-nl vol before and after passive deflection of a vibrissa, which results in localized displacements of the mechanoreceptor cells, primarily in the radial and polar directions about the vibrissa. These displacements are used to compute the strain field across the follicle in response to the deflection. We observe compression in the lower region of the RS, whereas dilation, with lower magnitude, occurs in the upper region, with volumetric strain ΔV/V ∼ 0.01 for a 10° deflection. The extrapolated strain for a 0.1° deflection, the minimum angle that is reported to initiate a spike by primary neurons, corresponds to the minimum strain that activates Piezo2 mechanoreceptor channels., (Copyright © 2015 the American Physiological Society.)

Electrical stimulation of the median nerve at the wrist may elicit a blink reflex [hand blink reflex (HBR)] mediated by a neural circuit at brain stem level. As, in a Sherringtonian sense, the blink reflex is a defensive response, in a series of experiments we tested, in healthy volunteers, whether and how the HBR is modulated by the proximity of the stimulated hand to the face. Electromyographic activity was recorded from the orbicularis oculi, bilaterally. We observed that the HBR is enhanced when the stimulated hand is inside the peripersonal space of the face, compared with when it is outside, irrespective of whether the proximity of the hand to the face is manipulated by changing the position of the arm (experiment 1) or by rotating the head while keeping the arm position constant (experiment 3). Experiment 2 showed that such HBR enhancement has similar magnitude when the participants have their eyes closed. Experiments 4 and 5 showed, respectively, that the blink reflex elicited by the electrical stimulation of the supraorbital nerve, as well as the N20 wave of the somatosensory evoked potentials elicited by the median nerve stimulation, are entirely unaffected by hand position. Taken together, our results provide compelling evidence that the brain stem circuits mediating the HBR in humans undergo tonic and selective top-down modulation from higher order cortical areas responsible for encoding the location of somatosensory stimuli in external space coordinates. These findings support the existence of a "defensive" peripersonal space, representing a safety margin advantageous for survival.

Intraneural microneurography and microstimulation were performed on single afferent axons in the inferior alveolar and lingual nerves innervating the face, teeth, labial, or oral mucosa. Using natural mechanical stimuli, 35 single mechanoreceptive afferents were characterized with respect to unit type [fast adapting type I (FA I), FA hair, slowly adapting type I and II (SA I and SA II), periodontal, and deep tongue units] as well as size and shape of the receptive field. All afferents were subsequently microstimulated with pulse trains at 30 Hz lasting 1.0 s. Afferents recordings whose were stable thereafter were also tested with single pulses and pulse trains at 5 and 60 Hz. The results revealed that electrical stimulation of single FA I, FA hair, and SA I afferents from the orofacial region can evoke a percept that is spatially matched to the afferent's receptive field and consistent with the afferent's response properties as observed on natural mechanical stimulation. Stimulation of FA afferents typically evoked sensations that were vibratory in nature; whereas those of SA I afferents were felt as constant pressure. These afferents terminate superficially in the orofacial tissues and seem to have a particularly powerful access to perceptual levels. In contrast, microstimulation of single periodontal, SA II, and deep tongue afferents failed to evoke a sensation that matched the receptive field of the afferent. These afferents terminate more deeply in the tissues, are often active in the absence of external stimulation, and probably access perceptual levels only when multiple afferents are stimulated. It is suggested that the spontaneously active afferents that monitor tension in collagen fibers (SA II and periodontal afferents) may have the role to register the mechanical state of the soft tissues, which has been hypothesized to help maintain the body's representation in the central somatosensory system.

Chemical activation and sensitization of trigeminal primary afferent neurons innervating the intracranial meninges have been postulated as possible causes of certain headaches. This sensitization, however, cannot explain the extracranial hypersensitivity that often accompanies headache. The goal of this study was to test the hypothesis that chemical activation and sensitization of meningeal sensory neurons can lead to activation and sensitization of central trigeminal neurons that receive convergent input from the dura and skin. This hypothesis was investigated by recording changes in the responsiveness of 23 [16 wide-dynamic range (WDR), 5 high threshold (HT), and 2 low threshold (LT)] dura-sensitive neurons in nucleus caudalis to mechanical stimulation of their dural receptive fields and to mechanical and thermal stimulation of their cutaneous receptive fields after local application of inflammatory mediators or acidic agents to the dura. Responses to brief chemical stimulation were recorded in 70% of the neurons; most were short, lasting the duration of the stimulus only. Twenty minutes after chemical stimulation of the dura, the following changes occurred: 1) 95% of the neurons showed significant increases in sensitivity to mechanical indentation of the dura: their thresholds to dural indentation changed from 1.57 to 0.49 g (means, P < 0.0001), and the response magnitude to identical stimuli increased by two- to fourfold; 2) 80% of the neurons showed significant increases in cutaneous mechanosensitivity: their responses to brush and pressure increased 2.5- (P < 0.05) and 1. 6-fold (P < 0.05), respectively; 3) 75% of the neurons showed a significant increase in cutaneous thermosensitivity: their thresholds to slow heating of the skin changed from 43.7 +/- 0.7 to 40.3 +/- 0.7 degrees C (P < 0.005) and to slow cooling from 23.7 +/- 3.3 to 29.2 +/- 1.8 degrees C (P < 0.05); 4) dural receptive fields expanded within 30 min and cutaneous receptive fields within 2-4 h; and 5) ongoing activity developed in WDR and HT but not in LT neurons. Application of lidocaine to the dura abolished the response to dural stimulation but had minimal effect on the increased responses to cutaneous stimulation (suggesting involvement of a central mechanism in maintaining the sensitized state). Antidromic activation (current of <30 muA) of dura-sensitive neurons revealed projections to the hypothalamus, thalamus, and midbrain. These findings suggest that chemical activation and sensitization of dura-sensitive peripheral nociceptors could lead to enhanced responses in central neurons and that this central sensitization therefore could result in extracranial tenderness (mechanical and thermal allodynia) in the absence of extracranial pathology. The projection targets of these neurons suggest a possible role in mediating the autonomic, endocrine, and affective symptoms that accompany headaches.

Surprisingly little is known concerning the central processing of innocuous thermal somatosensory information. The aim of the present study was to obtain quantitative data on the characteristics of neurons in the rat superficial medullary dorsal horn (sMDH) that responded to innocuous thermal stimulation of the rat's face and tongue. Single-unit extracellular recordings were obtained in chloralose-urethane anesthetized rats. A total of 153 thermoreceptive neurons was studied. Of these, 146 were excited by cooling and inhibited by warming and were classified as COLD cells. The remaining seven cells were excited by innocuous warming of the skin or tongue. Of 123 COLD cells tested, 33% were excited by touch and 22% by pinch stimuli delivered to the thermoreceptive field. Of the 50 COLD cells tested, 46% were excited also by noxious heating (> or = 50 degrees C for 5 s). Most (82/121) of the receptive fields were located on the upper lip, 25 on the tongue, and most of the remaining on the lower lip. Receptive fields were generally small (1-5 mm2). In some experiments, electrical stimulation in the thalamus was performed, and nine COLD cells could be activated antidromically. The responses of 38 COLD cells to incremental 5 degrees C cooling steps were examined quantitatively. Thermal stimuli were applied to facial or lingual receptive fields of sMDH neurons with a computer-controlled Peltier thermode starting from 33 degrees C, decreasing to 8 or 3 degrees C, and returning to 33 degrees C. Most COLD cells (26/38) had both static and dynamic responses; 7 had mainly dynamic and 5 mainly static responses to step decreases in temperature. Rat sMDH COLD cells could be classified into three groups depending on their stimulus-response functions. The first group (Type 1, n = 19) had a bell-shaped static stimulus response function. The second group (Type 2) had a high maintained or increasing static firing rate as the temperature decreased < 18 degrees C (n = 10). Type 3 COLD cells had mainly dynamic properties (n = 7). Many of the cells in all groups were excited by noxious mechanical stimulation. Type 2 cells differed from the other two groups in that most did not respond to noxious thermal stimuli (hot) and many responded to innocuous tactile stimuli. Neurons from each of the three groups of COLD cells could be activated antidromically from contralateral thalamus. These data suggest that there is little central processing of thermal information at the first central synapse for Type 1 neurons, however, the responses of the other two types may be due to central processing and convergence. The demonstration of rat sMDH COLD cells with distinctive stimulus-response functions to thermal shifts suggests separate functional roles of these neurons in the ascending thermal sensory pathway.

In macaque ventral premotor cortex, we recorded the activity of neurons that responded to both visual and tactile stimuli. For these bimodal cells, the visual receptive field extended from the tactile receptive field into the adjacent space. Their tactile receptive fields were organized topographically, with the arms represented medially, the face represented in the middle, and the inside of the mouth represented laterally. For many neurons, both the visual and tactile responses were directionally selective, although many neurons also responded to stationary stimuli. In the awake monkeys, for 70% of bimodal neurons with a tactile response on the arm, the visual receptive field moved when the arm was moved. In contrast, for 0% the visual receptive field moved when the eye or head moved. Thus the visual receptive fields of most "arm + visual" cells were anchored to the arm, not to the eye or head. In the anesthetized monkey, the effect of arm position was similar. For 95% of bimodal neurons with a tactile response on the face, the visual receptive field moved as the head was rotated. In contrast, for 15% the visual receptive field moved with the eye and for 0% it moved with the arm. Thus the visual receptive fields of most "face + visual" cells were anchored to the head, not to the eye or arm. To construct a visual receptive field anchored to the arm, it is necessary to integrate the position of the arm, head, and eye. For arm + visual cells, the spontaneous activity, the magnitude of the visual response, and sometimes both were modulated by the position of the arm (37%), the head (75%), and the eye (58%). In contrast, to construct a visual receptive field that is anchored to the head, it is necessary to use the position of the eye, but not of the head or the arm. For face + visual cells, the spontaneous activity and/or response magnitude was modulated by the position of the eyes (88%), but not of the head or the arm (0%). Visual receptive fields anchored to the arm can encode stimulus location in "arm-centered" coordinates, and would be useful for guiding arm movements. Visual receptive fields anchored to the head can likewise encode stimuli in "head-centered" coordinates, useful for guiding head movements. Sixty-three percent of face + visual neurons responded during voluntary movements of the head. We suggest that "body-part-centered" coordinates provide a general solution to a problem of sensory-motor integration: sensory stimuli are located in a coordinate system anchored to a particular body part.

1. We have demonstrated recently that reversible, cooling-induced inactivation of the face primary somatosensory cortex (SI) severely impairs the successful performance of a tongue-protrusion task but has relatively minor effects on the performance of a biting task. In an attempt to establish a neuronal correlate for these different behavioral relations, the present study was initiated to document the mechanoreceptive field properties of a population of face SI neurons and their activity during the tongue-protrusion and biting tasks. 2. Within SI, the representation of the face was found immediately lateral to that of the hand, and there was a clear somatotopic pattern of organization within face SI: the periorbital or nose region was located most medially in the face SI, then followed laterally in sequence the representation of the upper lip, lower lip, and intraoral area. A mechanoreceptive field (RF) was identified for 253 neurons, which included 162 "lip RF" neurons receiving mechanosensitive afferent inputs from the upper lip, lower lip, or both; 72 "tongue RF" neurons that received mechanosensitive afferent inputs from the tongue; 11 "periodontium RF" neurons receiving periodontal inputs; and 8 neurons that received inputs from other orofacial regions. 3. Nearly all (249/253) of the face SI neurons responded to light tactile stimuli, and most of them received contralateral inputs (78%) and showed a rapidly adapting (RA) response to tactile stimulation (82%). There was no significant difference in the ratio of slowly adapting (SA) to RA neurons in areas 3b and 1. 4. For 193 neurons studied in one or both of the orofacial tasks, 113 were found, on the basis of histological reconstruction, to be distributed in area 1, 61 in area 3b, and 19 in area 2. 5. The firing rate of most tongue RF (79% of 56) neurons and lip RF (60% of 93) neurons tested was significantly altered during the tongue-protrusion task. Only some (14% of 36 tongue RF neurons and 34% of the 92 lip RF neurons tested) showed a significant change in firing rate during the biting task. Three of 7 periodontium RF neurons studied in the tongue-protrusion task altered their firing rate and 5 of 10 altered their firing rate during the biting task. 6. Most of the 116 face SI neurons studied during both tasks exhibited a preferential relation to the tongue-protrusion task as distinct from the biting task, and none showed task-related activity during the biting task only.(ABSTRACT TRUNCATED AT 400 WORDS)

1. In previous papers we have presented evidence suggesting an important role for the face primary somatosensory cortex (SI) in the fine control of tongue movements. These findings, plus our earlier evidence that many neurons in face motor cortex (MI) may exhibit firing rates related to the direction of tongue protrusion, led us to test the hypothesis that variations in the direction of a tongue-protrusion movement would be associated with variations in the activity of different face SI neurons. 2. Two monkeys were trained to perform a tongue-protrusion task in each of three directions: the task transducer was positioned at 0 degrees, 30 degrees to the left, or 30 degrees to the right from the midsagittal plane. The latter two positions were termed asymmetrical tongue-protrusion task positions. Single-neuron activity was recorded from face SI during trials of the tongue-protrusion task at each of two or three of the above positions. In addition, the mechanoreceptive field (RF) was delineated for each neuron. 3. Directional relations were found in 25 (58%) of the 43 neurons studied; this included 20 neurons showing a significant direction-by-time interaction in firing rate, i.e., the change of firing rate from the pretrial period to the task period was significantly different between different directions, and 5 showing no direction-by-time interaction but a significant difference in firing rate between different directions of the tongue-protrusion task. 4. Of the 43 neurons investigated, 21 and 20 had a RF on the tongue and lips, respectively ("tongue RF" and "lip RF" neurons), and the remaining 2 received mechanosensitive afferent inputs from other orofacial regions. There was no significant difference in the incidence of directional sensitivity between the neurons with a tongue RF and those with a lip RF (12/21 and 11/20, respectively). 5. Eight of the 25 "directional" neurons were located in area 3b and 17 in area 1. There was no significant difference in the proportion of directional neurons between areas 3b and 1. 6. The increase in discharge frequency at the preferred direction was, on the average for the 25 directional neurons, 39% over the mean discharge frequency observed during the task period for all directions of the tongue-protrusion task. Eight directional neurons showed a significant increase in firing rate during the tongue-protrusion task up to 130 ms before the onset of genioglossus electromyographic activity.(ABSTRACT TRUNCATED AT 400 WORDS)

1. In previous papers we have demonstrated that most single neurons in the face primary somatosensory cortex (SI) alter their firing rate during a trained tongue-protrusion task and some also during a trained biting task. Although the data suggest that some of the task-related activity in face SI might conceivably come from reafferent inputs from moving orofacial structures, it is possible that orofacial inputs are modulated during the trained orofacial movements. This study was initiated to investigate the possible modulation of evoked orofacial somatosensory responses of face SI neurons during trained tongue-protrusion and biting tasks. 2. Two monkeys were trained to perform a tongue-protrusion and a biting task and to accept stimulation applied to the facial skin or the lingual nerve during the tasks. For SI neurons with a tongue mechanoreceptive field (RF), electrical stimulation was applied to the lingual nerve to elicit neuronal activity; for SI neurons with a RF at the other locations, electrical or mechanical stimulation was applied to the RF to elicit neuronal activity. Modulation of neuronal activity evoked by low-threshold stimulation of the RF was tested, during the tongue-protrusion and/or biting tasks, in 44 face SI neurons and an additional 3 forelimb SI neurons with a palm RF (palm RF neurons). The 44 face SI neurons included 13 with a tongue RF (tongue RF neurons), 29 with a lip RF (lip RF neurons), and 2 with a lateral face RF (face RF neurons). 3. For face SI neurons tested during both force dynamic and holding phases of the task period, the evoked activity (i.e., the number of evoked spikes in 50 ms after the onset of stimulation) was decreased in at least one of the two phases for the majority (90%) of 31 neurons studied during the tongue-protrusion task and 61% of 23 studied during the biting task. The proportion of neurons modulated during the tongue-protrusion task was significantly higher than that during the biting task. For the 18 face SI tested during both tasks, a decrease in evoked activity occurred in 10 lip RF neurons for both tasks and in the remaining 5 lip RF and 3 tongue RF neurons for the tongue-protrusion task only. No neurons tested showed a clear facilitation of evoked activity during the task period of either task.(ABSTRACT TRUNCATED AT 400 WORDS)

1. Most quantitative examinations of nociception are performed with thermal or mechanical stimuli. Because nociceptive processing mechanisms may depend on the modality of the stimuli, comparable studies on chemonociception are necessary. 2. We examined the activity of chemonociceptive medullary dorsal horn neurons in halothane-anesthetized rats. For controlled noxious chemical stimulation, defined CO2 pulses were applied to the nasal mucosa. The effects of stimulus intensity, duration, and interstimulus interval (ISI) were tested by performing three different CO2 stimulation protocols (see below). 3. The recorded neurons were characterized by intranasal and facial stimuli of different modalities. The cells received input from intranasal A delta- and/or C-fibers. All tested neurons also responded to other intranasally applied irritants, e.g., mustard oil. Furthermore, the units were sensitive to intranasal high-threshold mechanical stimulation and to facial mechanical stimulation. According to the properties of their facial mechanoreceptive fields, the units were classified as wide dynamic range (WDR) or nociceptive specific (NS) neurons. The majority of the cells also responded to facially applied noxious heat stimuli, so that most of the recorded neurons were found to be multimodal. Some of the neurons, in addition, had convergent input from primary afferents innervating the maxillary tooth pulps or the cornea and periorbital structures. 4. In the first stimulation protocol we presented four different CO2 concentrations (25, 50, 75, and 100%; stimulus duration 2 s). In total, each concentration was applied 10 times (2 trains of 5 stimuli). Stimulus response functions (SRFs) were computed with average responses to identical stimuli. All but 2 of the 23 tested neurons displayed enhanced responses after stimulation with increasing intensities. In general, WDR cells (n = 15) discharged more vigorously to the same CO2 concentration than NS cells (n = 8). WDR neurons discriminated more reliably between stimulus intensities in the low to moderate range (25-50% CO2) than NS cells. Both categories of neurons, however, discriminated equally well in the moderate- to high-intensity range (50-75% CO2). The discriminatory capacity of WDR and NS neurons was reduced in the highest concentration range (75-100% CO2). The proportion of NS neurons significantly discriminating between these intensities tended to be higher compared with WDR neurons when stimuli were applied with long ISIs (120 s). 5. To examine the effects of the duration of the ISI, identical test sequences were performed with ISIs of 30 and 120 s. (ABSTRACT TRUNCATED AT 400 WORDS)

1. Intra-axonal recording, receptive field mapping, horseradish peroxidase injection, cytochrome oxidase staining, and computer-assisted reconstruction/morphometric methods were used to elucidate the structure and topography of trigeminal primary afferent collaterals in the normal adult rat. Prior studies focused on trigeminal brain stem subnuclei interpolaris and caudalis. This work is extended here to the remaining 2 subnuclei, principalis (PrV) and oralis (SpVo), where collaterals from 66 axons in 37 adult rats were studied. In nine rats, three to five axons were stained for within-nucleus comparisons of different fibers. Quantitative analyses were restricted to vibrissa sensitive fibers. 2. All of the axons conducted rapidly with small, low-threshold receptive fields. The majority responded to vibrissa deflection (n = 47); the remainder responded to guard hair deflection; gentle pressure applied to hairy skin, glabrous skin, lingual mucosa, or an incisor; or jaw movement. All descended in the trigeminal sensory root where some bifurcated into ascending and descending branches. Each well-stained fiber gave rise to transversely oriented collaterals in PrV and SpVo. 3. Within PrV and SpVo, fibers with differing adaptation properties and receptive fields had indistinguishable collateral morphologies. Arbors from single axons were rostrocaudally discontinuous, small relative to collaterals in subnuclei interpolaris and caudalis, circumscribed and topographically organized in a manner consistent with cytochrome oxidase and bulk-labeled primary afferent staining patterns. In SpVo and caudal PrV, the map is inverted with the nose pointing medially. In rostral PrV, the map turns 90 degrees such that the nose points dorsally. 4. Axons had different quantitative properties along the rostrocaudal axis of the trigeminal brain stem complex. Whereas arbors subtended similar transverse areas throughout PrV and SpVo, collaterals in the rostral third of PrV had a relatively low bouton density. Arbors in the caudal two thirds of PrV had the highest bouton density. Arbors in SpVo tended to be more variable in size and shape than those of caudal PrV, and their bouton numbers were significantly lower than in PrV. 5. In PrV, arbors were largely confined to somatotopically corresponding cytochrome oxidase patches, precluding significant overlap of neighboring whisker projections. In SpVo, termination sites were not as strictly confined and numerous examples of within- and between-row overlap were obtained for whisker afferents in cases where multiple axons were stained.(ABSTRACT TRUNCATED AT 400 WORDS)

1. To examine further the ability of different classes of nociceptive and nonnociceptive primary afferent neurons to induce c-fos expression in central neurons, fos-like immunoreactivity was examined in the medullary dorsal horn (laminae I-IV) of the rat after facial application of a range of warming and cooling thermal stimuli. Urethan-anesthetized rats received 15 30-s thermal pulses (53, 50, 47, 41, 25, or 10 degrees C) applied to the vibrissal pad over a period of 30 min and were perfused 2 h after the end of stimulation. 2. Stimulation of 41 degrees C produced no significant increase in the number of fos-LI-labeled cells in lamina I or II compared with control (35 degrees C) animals. 3. Stimulation of 47 degrees C produced a significant increase in the number of fos-LI-labeled cells in both laminae I and II. Stimulation of 50 degrees C produced a significant increase in labeling, compared with that produced by 47 degrees C, which was primarily in lamina II. Stimulation of 53 degrees C produced no further increase in the number of labeled cells, compared with that produced by 50 degrees C, in lamina I or II. 4. In the cooling direction, 25 degrees C produced a significant increase in labeling above control levels in both lamina I and II, whereas 10 degrees C produced a further increase compared with 25 degrees C, which was restricted to lamina I. 5. None of the stimuli produced a significant increase in labeling in laminae III-IV. 6. The results are interpreted as providing evidence that low-threshold cold receptors, high-threshold cold receptors, and nociceptors are capable of inducing fos expression in dorsal horn neurons, whereas warm receptors are relatively ineffective. The results also provide evidence that neurons that receive input from C polymodal nociceptors are present in both laminae I and II, as are neurons that receive input from low-threshold cold receptors. Neurons that receive input from high-threshold cold receptors, but not from low-threshold cold receptors, appear to be located preferentially in lamina I. The shape of the curve relating fos-LI labeling to stimulus temperature in the warming direction is consistent with the expected pattern of recruitment of primary afferent nociceptors.

1. Studies using ablation, intracortical microstimulation (ICMS) and surface stimulation, and single-neuron recordings have suggested that the primate primary somatosensory cortex (SI) may play an important role in movement control. Our aim was to determine whether bilateral inactivation of face SI would indeed interfere with the control of tongue or jaw-closing movements. 2. Effects of reversible inactivation by cooling of face SI was investigated in two monkeys trained to perform both a tongue-protrusion task and a biting task. The cooling experiments were carried out after the orofacial representation within SI was identified by systematically defining the mechanoreceptive field of single neurons recorded in face SI. The deficits in the tongue or jaw-closing movement were evaluated by the success rates for the monkeys' performance of both tasks and by the force and electromyographic (EMG) activity recorded from the masseter, genioglossus, and digastric muscles associated with the tasks. 3. During bilateral cooling of face SI, there was a statistically significant reduction in the success rates for the performance of the tongue-protrusion task in comparison with control series of trials while the thermodes used to cool face SI were kept at 37 degrees C. Detailed analyses of force and EMG activity showed that the principal deficit was the inability of the monkeys to maintain a steady tongue-protrusive force in the force holding period during each trial and to exert a consistent tongue-protrusion force between different trials. The task performance returned to control protocol levels at 4 min after commencement of rewarming. 4. Identical cooling conditions did not significantly affect the success rates for the performance of the biting task. Although the extent of the deficit was not severe enough to cause a significant reduction in successful rates for the biting task, cooling did significantly affect the ability of the monkeys to maintain a steady force in the holding period during each trial and to exert a consistent force between different trials. In one monkey the success rate of the biting task was also not affected by bilaterally cooling of face SI with a pair of larger thermodes placed on the dura over most of the face SI, face primary motor cortex (face MI), and adjacent cortical regions.(ABSTRACT TRUNCATED AT 400 WORDS)

1. The role of the thalamic ventroposterior medial (VPM) nucleus in the discriminative aspects of nociception and thermoreception was evaluated in alert, trained rhesus monkeys. Single-unit responses were recorded from VPM while the monkeys performed a battery of tasks involving noxious heat, innocuous cool, and air-puff stimuli presented to the face. The discriminative ability of the monkey was compared directly with the responses of single neurons, to determine whether the neuronal response could subserve the monkey's discriminative behavior. 2. Most thermally sensitive neurons exhibited multimodal properties. Only 18% responded exclusively to heat (HT-Heat neurons), whereas 27% responded to innocuous mechanical, as well as noxious mechanical and heat stimuli (WDR-Heat). Twenty-three percent responded to innocuous mechanical stimuli and innocuous skin cooling (Mechano-Cool), and 32% responded to mechanical, innocuous cool, and noxious heat stimuli (WDR-Heat-Cool). 3. Almost all mechanical receptive fields were confined to one division of the trigeminal nerve. This was true for all of the above categories of VPM neurons, even those showing highly convergent properties (WDR-Heat-Cool). 4. Heat-activated neurons produced graded responses to noxious skin heating in the 46 to 49 degrees C range. Stimulus-response functions of neurons that responded to both heat and cool did not differ from those of neurons that responded exclusively to skin heating. 5. When the monkeys were detecting small changes in the intensity of a noxious heat stimulus (e.g., from 47 to 47.1-47.8 degrees C), heat-activated neurons responded to the smallest temperature changes that could be detected by the monkeys. Further, there was a high correlation between the monkey's success in detecting the stimulus changes and the magnitude of the neuronal responses to those changes. 6. Although the responsiveness of VPM cool-activated neurons was not compared with the monkeys' threshold for detecting cooling changes, larger stimulus changes (2 degrees C) that the monkey reliably detected produced significant neuronal responses. Further studies are needed to determine whether VPM neurons respond to the smallest detectable changes in skin cooling. 7. Several thermally sensitive VPM neurons were tested under two attentional conditions: 1) while the monkey was required to attend to a visual stimulus, and 2) while it was required to attend to the thermal stimulus to obtain reward. None showed a significant difference in heat- or cool-evoked activity in the two attentional states.(ABSTRACT TRUNCATED AT 400 WORDS)

1. Single-unit activity was recorded in the ventral posterior medial (VPM) thalamic nucleus of awake monkeys while they performed detection and discrimination tasks involving tactile air-puff stimuli presented to the face. Neuronal responsiveness was compared directly with the monkey's discriminative performance. In addition, neuronal activity was compared when the monkey's attention was directed to the air-puff stimulus and when it was directed to a concurrent visual stimulus. 2. Neurons responding to the air-puff stimuli were classified as slowly adapting (SA), rapidly adapting (RA), inhibitory (IN), or multimodal (MM), according to their responses to manual and thermal stimulation, as well as their adaption rates to the air puff. Of 47 neurons responsive to air-puff stimulation and studied extensively in the behavioral task, 14 were classified as RA, 15 as SA, 6 as IN, and 12 as MM. The 12 MM neurons were so classified because, in addition to air puff, they responded to noxious heat, innocuous cooling, or noxious pinch. 3. Neurons from each class had restricted contralateral receptive fields localized within one division of the trigeminal nerve. There was no systematic difference in receptive-field size among groups. 4. A prominent difference in tactile responsiveness of MM neurons was response latency. Although the mean latency for RA, SA, and IN neurons was not significantly different (6.1, 9.1, and 12.2 ms, respectively), the mean latency for MM neurons was significantly longer than that for each of the other neuronal categories (28.8 ms; Ps < 0.001). These data suggest that the excitatory tactile afferent input to MM neurons is different from that to low-threshold neurons. 5. For RA, SA, and MM neurons the frequency of the neuronal discharge evoked by the air-puff stimulation was proportional to the intensity of the air puff. Thus responses of each neuronal class coded air-puff stimulus intensity. 6. The monkeys' ability to detect air-puff stimuli of various intensities was compared with the frequency of neuronal responses to those stimuli. Both the percent success in detecting differences in air-puff intensity and the detection latency were highly correlated with neuronal response frequency. The responses of all three excitatory neuronal categories corresponded well with the monkey's performance. Thus any or all of RA, SA, and MM neurons could play a role in the discrimination of air-puff intensities.(ABSTRACT TRUNCATED AT 400 WORDS)

1. Cats were prepared for chronic recording from neurons in pars oralis and pars interpolaris of the trigeminal spinal nucleus. Electrodes were implanted into canine teeth for electrical stimulation and the digastric muscle for recording electromyograms. 2. Recordings were made from the animals when they were awake and unrestrained as well as when they were lightly anesthetized. Some neurons were studied under both conditions. 3. In an awake animal, single tooth-pulp stimuli of 0.1 ms duration and < or = 1 mA intensity produced no aversive behavior. 4. The response of trigeminal brain stem neurons in the awake animal to such stimuli consisted of short (approximately 3 ms)- and long (approximately 25 ms)-latency discharges whose thresholds suggested that they were both due to inputs from fast conducting primary afferent fibers. 5. Light anesthesia reduced the number of impulses in both components and in most cases completely abolished the long-latency component evoked by low-intensity stimuli. The threshold of the short-latency component was little affected by light anesthesia. It is postulated that the short-latency component is mediated by a monosynaptic input from primary afferent fibers and the long-latency component by a polysynaptic input from these same fibers. 6. All neurons that responded to tooth-pulp stimulation had inputs from other orofacial sites both in the awake and lightly anesthetized states. After light anesthesia, these receptive fields were altered in only 3 out of 15 neurons. 7. The majority of neurons (18 out of 20) were not spontaneously active in the awake animal. Spontaneous activity in the other two was reduced by light anesthesia. 8. The threshold of the digastric reflex evoked by tooth-pulp stimulation was not altered by light anesthesia, but the size of the response was reduced. 9. The effects of changing the level of anesthesia from deep to light (i.e., without and with reflex withdrawal to squeezing a paw) on the responses to tooth-pulp stimulation were also studied. Decreasing the anesthetic depth tended to decrease the thresholds and increase the magnitude of both the short- and long-latency neuronal responses and the short-latency digastric response.

1. We have recently demonstrated that reversible, cooling-induced inactivation of the face motor cortex results in a severe impairment in the ability of monkeys (Macaca fascicularis) to perform a tongue-protrusion task but produces only relatively minor effects on the performance of a biting task by the same monkeys. To establish a neuronal correlate for these different behavioral relations, the present study has detailed the afferent input and intracortical microstimulation (ICMS)-defined output features of a population of face motor cortical neurons, and in a subsequent study we have documented the activities of the same population of neurons during the performance of the tongue-protrusion and biting tasks. 2. Of the 231 single neurons recorded within the face motor cortex, 163 were located at sites from which ICMS (less than or equal to 20 microA) could evoke tongue movements (i.e., "tongue-MI" sites) at the lowest threshold for eliciting orofacial movements. The remainder were located at sites from which ICMS evoked jaw movements ("jaw-MI" sites), face movements ("face-MI" sites), or at a few sites, tongue movements and, at the same threshold intensity, either a jaw movement or a facial movement. 3. We confirmed the general organizational features of the face motor cortex that have been defined in previous studies, but we documented in detail the organizational features for tongue-MI. Thus we found that tongue movements were well represented, whereas jaw-closing movements were poorly represented; the representations for face, jaw, and tongue movements were overlapped; the same ICMS-evoked tongue movement could be multiply represented within tongue-MI; tongue-MI was characterized by a prominent input from superficial mechanosensory afferents, whereas there was little evidence for deep input; a close spatial match was found between ICMS-defined motor output and somatosensory afferent input for tongue-MI. 4. A variety of tongue movements could be evoked by ICMS at tongue-MI sites and were categorized into protrusion, retrusion, laterally directed, and other types of tongue movement. Low-threshold (i.e., less than or equal to 5 microA) ICMS-defined tongue-MI sites, which were considered to represent "efferent zones" projecting relatively directly to motoneurons, were reconstructed three dimensionally to provide insights into the spatial organization of tongue-MI. Examples of each of the four low-threshold efferent-zone categories were usually found throughout the ICMS-defined tongue-MI without any apparent preferential distribution. Furthermore, different low-threshold efferent-zone categories had close spatial relationships to each other in cortex.(ABSTRACT TRUNCATED AT 400 WORDS)

1. In previous papers we presented evidence pointing to an important role for face motor cortex in the control of tongue movements. Intracortical microstimulation (ICMS) at many sites within face motor cortex evoked different types of tongue movement, and many neurons at these "tongue-MI" sites received intraoral mechanosensitive afferent input, and their activity was related to a tongue-protrusion task performed by a monkey. In view of the synergistic action of the various tongue muscles during tongue movement, we hypothesized that these different tongue-MI sites are recruited to effect the appropriate change in tongue shape and position during a tongue-protrusion movement. A prediction from this hypothesis is that variations in the direction of a tongue-protrusion movement should be associated with variations in the activities within the different tongue-MI efferent zones. Differences in efferent-zone activity should be reflected in differences in the firing rates of neurons that are located at these tongue-MI sites. 2. We trained two monkeys to perform a tongue-protrusion task at each of three directions. The tongue-protrusion task transducer was positioned at 0 degrees (Ts), 30 degrees to the left (Tlt), or 30 degrees to the right (Trt) from the midsagittal plane; the latter two positions were termed asymmetric tongue-protrusion task positions. Single neurons were recorded from tongue-MI during trials of tongue-protrusion task at each of two or three of the above positions. Some of the neurons were also studied during a biting task. In addition, neurons were tested for possible mechanosensitive afferent input. 3. Of the 66 neurons studied, 31 (45%) exhibited directional relations; that is, the change in firing rate between the pretrial period (PTP) and the task period for the tongue-protrusion task was significantly different for each neuron depending on the direction in which the activity of the neuron was studied. 4. The "directional" neurons exhibited a single preferred direction of firing in that the mean firing rate during one direction of tongue-protrusion task was significantly greater than for any other direction. Of the 20 neurons studied at all three directions of tongue-protrusion task, the mean firing rate of each of 18 was highest at one of the asymmetric positions, and 12 of these 18 neurons exhibited a monotonic decrease in absolute firing frequency from one asymmetric task direction to the other. 5. Thirteen of the neurons were also studied while the monkey performed the biting task. Most tongue-MI directional neurons were not related to the biting task.(ABSTRACT TRUNCATED AT 400 WORDS)

1. The previous paper has described in detail the input and output features of single neurons located at sites within primate face motor cortex from which intracortical microstimulation (ICMS, less than or equal to 20 microA) evoked tongue movements at the lowest threshold ("tongue-MI" sites); for comparative purposes, we also reported on the input and output features of a smaller number of neurons recorded at sites from which ICMS could evoke jaw movements ("jaw-MI" sites), facial movements ("face-MI" sites), or, at a few sites, tongue movements and, at the same threshold intensity, either a jaw movement or a facial movement. 2. Our findings of an extensive and diverse representation of sites within face motor cortex of monkeys for the generation of elemental components of tongue movement, and the relatively few sites from which jaw-closing movements could be evoked, were consistent with our recent observations that reversible, cooling-induced inactivation of the face motor cortex severely impaired the performance by monkeys of a tongue-protrusion task but had only relatively minor effects on the performance of a biting task. In an attempt to establish a neuronal correlate for these different behavioral relations, the present study has documented the task-related activities of those single neurons that were characterized in the previous paper in terms of afferent input and ICMS-defined output features. 3. Each task required the development and maintenance by each monkey of a fixed force level for a minimum period of time to obtain a fruit-juice reward. During one or both of these tasks, we characterized the activities of 231 single face motor cortical neurons that were located at the above-mentioned ICMS-defined sites. Neurons were said to be related to a particular task if they showed statistically significant differences in firing rates during the task in comparison with a control pretrial period (PTP). 4. In tongue-MI, there was a significantly higher proportion of neurons (63% of 156 neurons tested) that were related to the tongue-protrusion task than to the biting task (15% of 65). However, in jaw-MI the proportion of neurons that were biting task-related (63% of 19) was significantly higher than the proportion related to the tongue-protrusion task (11% of 9); the proportion of biting task-related neurons at ICMS-defined jaw-closing sites was also higher than that at jaw-opening sites.(ABSTRACT TRUNCATED AT 400 WORDS)

1. Twenty-six nociceptive neurons in the primary somatosensory cortex (SI) of anesthetized monkeys were responsive to noxious thermal stimulation applied to the face. Thermode temperature increased from a base line of 38 degrees C to temperatures ranging from 44 to 49 degrees C (T1). After a period of 5 s, the temperature increased an additional 1 degree C (T2). The neuronal responses to noxious thermal stimuli were compared when the interstimulus interval (ISI) was 30 or 180 s. 2. A linear regression analysis was applied to the stimulus-response functions of neuronal responses to T1 stimuli obtained at ISIs of 180 s. Based on the slopes and linear regression coefficients of these stimulus-response functions, two populations of nociceptive neurons were identified. The neuronal responses of one population of nociceptive SI neurons (WDR1) to T1 stimuli were characterized by steep slopes and high regression coefficients, whereas the other population (WDR2) had flatter slopes and lower regression coefficients. WDR1 neurons responded with monotonic increases in neuronal activity as the stimulus intensity increased. However, the peak frequency of WDR2 neurons often reached a plateau below 47 degrees C. Both WDR1 and WDR2 neurons had receptive fields that encompassed one or two divisions of the trigeminal nerve. 3. The T1 neuronal responses of WDR1 neurons were significantly suppressed when thermal stimuli were delivered with ISIs of 30 s. The T1 neuronal responses of WDR2 and the T2 responses of both WDR1 and WDR2 neurons were not significantly different when ISIs of 30 and 180 s were used. The T1 thresholds of WDR1 and WDR2 neurons were significantly higher when stimuli were delivered with ISIs of 30 s compared with ISIs of 180 s. 4. Most nociceptive SI neurons were located in layers III and IV of area 1-2. In a number of instances, multiple nociceptive neurons were found in the same microelectrode penetration. 5. The humans' intensity of pain sensation paralleled the neuronal responses of nociceptive SI neurons. With the use of a similar paradigm as in the monkey experiments, increases in T1 and T2 temperatures resulted in monotonic increases in pain ratings and change in pain sensation, respectively. However, the intensity of pain sensation to T1 temperatures was suppressed by ISIs of 30 s. Neither ISI produced statistically significant changes in the intensity of pain sensation to T2 stimuli. 6. These data demonstrate that manipulations that alter the intensity of pain sensation also produce concomitant changes in the responsiveness of nociceptive SI neurons.(ABSTRACT TRUNCATED AT 400 WORDS)

1. Rats were irradiated by 200 R of X ray on day 17 (the 18th day) of gestation through the body wall of the mother. When they underwent the following electrophysiological tests at the age of 3-4 mo, the somatosensory cortex showed a lack of layers II, III, IV, and Va, as described by previous investigators (3, 4). 2. Spike responses to quick whisker deflections were recorded from single cells in the somatosenory cortex of normal and prenatally X-irradiated rats. 3. In normal animals, single units often responded to several whiskers, but the magnitudes (response latency and firing probability) of the responses were graded around a whisker in the "center" of the field that gave rise to the strongest response. During electrode penetration perpendicular to the cortical surface, such a center remained unchanged or shifted to another whisker that was immediately adjacent. As for the large-sized, initially positive unitary spikes (typically 2 mV or higher) sampled in this study, no systematic change in the response latency, the size of receptive field, or response probability was detected during the penetration. 4. The above description holds also for the irradiated rats except that the response latency was prolonged when compared to the normal controls. 5. Cortical laminar analysis of field potentials revealed that while the earliest electric sink appeared in layer IV in the controls, that in the irradiated rats was observed in layer Vb. However, there was no difference in the latency of these potentials between the two groups, suggesting that vibrissal sensory signals reach the cortical level normally even in the irradiated rats. The prolonged latency of the irradiated cortical neuronal response could thus be ascribed to an abnormal intracortical delay, which was most likely associated with the failure of development of layer IV stellate cells in these preparations. 6. A possibility as to how the layer IV stellate cells are involved in input-output relationships in the normal somatosensory cortex is presented and discussed.

The receptive field and submodality characteristics of individual neurons within the cytoarchitectural and topographic subdivisions of the head and face areas of the postcentral gyrus (SI) were determined with the technique of extracellular recording. Correlation of the single-unit data with the intracortical location of the recording electrode provided a detailed description of the functional organization within each of the several cytoarchitecturally distinct regions contributing to the representation of the head and face in SI. The data indicate that the functional organization of the SI cortex which receives its principal input from trigeminal mechanoreceptors is comparable to the organization within those SI regions which receive their input from the mechanoreceptors of the limbs, trunk, and tail. In each topographic subdivision of the SI cortex 1) a single region in the periphery is represented several times in widely separated locations, each time in a context of different submodalities and peripheral receptive fields; and 2) neurons belonging to the different submodality classes are segregated so that projections from cutaneous afferents terminate mainly in cytoarchitectural area 3 in the adjacent anterior portion of area 1, while projections from the afferents innervating deep tissues terminate mainly in cytoarchitectural area 3a, area 2, and the posterior part of each 1. Although the mechanoreceptor input to SI is segregated according to submodality and the mechanoreceptors from most body regions project to multiple widely separated regions within SI, neurons with receptive fields confined to the ophthalmic division of the trigeminal peripheral innervation field are found within a restricted region of the anterior postcentral gyral crown which is positioned symmetrically about the junction of cytoarchitectural areas 1 and 3. Neurons with receptive fields confined to the maxillary division of the trigeminal innervation field are found within a ring of cortex which a) completely surrounds the representation of the ophthalmic field, and b) includes parts of cytoarchitectural area 2, 1, 3, and 3a. SI neurons with receptive fields restricted to the mandibular division of the trigeminal innervation field occupy the largest portion of the SI face area and form a ring of cortical cell columns which completely surrounds that cortical region which receives its input from the maxillary peripheral innervation field.

Single-unit activity was recorded from the caudate nucleus (CD), globus pallidus, and entopeduncular nucleus (GP-ENTO) in awake, partially restrained kittens. The purpose of this experiment was to assess the ability of developing basal ganglia structures to process natural facial somatosensory information and compare this function to that observed in the adult. Somatosensory responsiveness in the CD and GP-ENTO developed slowly during the first three postnatal months. Somatosensory responsiveness had three major developmental trends in these nuclei: 1) The proportion of neurons responding to facial sensory stimulation increased with age; 2) proportionally, the area of face encompassing a receptive field of a neuron was smaller in adults than in young kittens; 3) qualitatively, adultlike responses to sensory stimulation did not appear until approximately three months of age. Units responsive to facial somatosensory stimulation in kittens under three months of age were very limited in the types of information they received. No specific stimuli parameters were encoded by these neurons. At approximately three months of age, units began to respond to varied stimuli (i.e., indentation of the skin as well as to brushing stimuli) and began to encode specific stimulus parameters such as direction of movement and relative location on the face. Kitten units responsive to skin indentation showed no evidence of encoding stimulus magnitude information. This was also true for the majority of adult basal ganglia neurons tested. The present findings suggest that the functions of the basal ganglia may be altered significantly during development. With increasing age, the basal ganglia may change from primarily a relay area for relatively nonspecific sensory information to an active processor of complex afferent information.

1. The response of C polymodal nociceptors to thermal and mechanical stimuli applied to the monkey's face was recorded extracellulary in the trigeminal ganglion in rhesus monkeys anesthetized with sodium pentobarbital. Conduction velocities, determined from electrical stimulation of receptive fields (RFs), were in the range for unmyelinated C fibers (mean=0.82 m/s, n=20; SD=+/-0.17). With two exceptions cutaneous RFs were single spots (median=2 mm2; n=37) and usually were identical for thermal and mechanical stimuli. The median force threshold for the sample of units was 1.2 g (von Frey technique; n = 39; range = 0.07-8.5 g). 2. Discharges to thermal stimuli were investigated with a feedback-controlled contact thermode which permitted temperature changes less than or equal 12.0 degrees C/s. Thermal thresholds ranged from 38 degree to 49 degree C (median=46 degrees C; n=37), and maximum discharge frequencies were obtained in the noxious heat range (45-55 degrees C). For a graded series of 5 s duration stimuli from an adapting temperature of 35 degrees C, the number of impulses increased as a monotonic function of stimulus intensity over the range from threshold temperature to 50-53 degrees C. Many stimulus-response functions were positively accelerated, and linear regression analyses showed that most units examined were best fit by nonlinear functions. 3. The typical pattern of activity to 5 s duration temperature shifts into the noxious heat range was a short accelerating burst of impulses followed by deceleration to a lower rate of discharge prior to termination of the stimulus. The temporal profile of the discharge of impulses was virtually identical at different adapting temperatures. In units tested with 30 s duration stimuli at 2-6 degrees C above threshold, the mean frequency of discharge during the final 25 s was 1.46 impulses/s (n=6; SD=+/-0.89). 4. Application of noxious heat stimuli a few degrees above threshold temperature typically sensitized or enhanced the response of the unit to subsequent application of heat stimuli. The signs of sensitization consisted of a decrease in threshold temperature, increased frequency of discharge, decreased latency to the first impulse, and afterdischarges. Units failed to respond throughout the duration of 30 s stimuli if the final temperature exceeded 50 degrees C. Depressed responses were sometimes produced by application of intense (greater than or equal 55 degrees C) stimuli, presumably as a result of partial inactivation of the receptor. 5. In a correlative analysis, the latency and pattern of discharge in a sample of units were compared with escape responses in two monkeys to temperature shifts into the noxious heat range (49 and 51 degrees C). The analysis revealed that the discharge of C polymodal nociceptors alone cannot account for fast escape responses, but the discharge may contribute to escape responses which occur more than 3.5 s after the onset of stimulation.

Extracellular recordings were made from cold-receptive afferent fibers in the trigeminal ganglion of rats anesthetized with halothane. By applying a standardized series of steady or changing temperatures to the receptive fields, we recorded the static and dynamic responses of the afferents. Comparable recordings were made from neurons in the marginal layer of the caudal trigeminal nucleus onto which the cold fibers synapse. The static and dynamic responses of the afferent fibers were reproduced faithfully by the second-order neurons, but at a much higher level of activity. Ganglionectomy silenced the second-order cells. Their continuous high level of activity appears to depend on the tonic input from the afferent fibers and not on any intrinsic circuits in the medulla.

1. The medulla oblongata caudal to the obex was explored with glass capillary microelectrodes filled with fast green dye in urethan-chloralose-anesthetized cats. Concurrently, the trigeminal integument was mechanically stimulated. Two classes of units, which were activated by innocuous mechanical stimulation of the ipsilateral trigeminal integument, were identified. Both of them showed a somatotopic organization. 2. Units maximally activated by tactile stimulation of a small receptive field in the ipsilateral trigeminal integument were located in pars magnocellularis of the trigeminal subnucleus caudalis. Receptive field falling within, the mandibular distribution were found in the dorsomedial part of pars magnocellularis, maxillary fields occurred next, and ophthalmic fields were represented ventrolaterally. The rostrum (the mouth and nose) was represented just behind the obex, and the receptive field represented gradually shifted to the periphery of the face along the rostrocaudal axis, finally proceeding to dermatomes of cervical segments. At each transverse plane, tactile sensation of the most rostral segment of the represented integument projected onto the marginal zone of pars magnocellularis immediately adjacent to substantia gelatinosa, while the most peripheral segment projected onto the core of quasi-semicircular pars magnocellularis. The result is in contrast with the scheme proposed by previous investigators. 3. Within the lateral part of subnucleus reticularis dorsalis medullae oblongatae, which is ventromedially contiguous with pars magnocellularis, trigeminal units homologous with lamina V units in the spinal dorsal horn were identified. Typically, these units had a graded response in the center of the receptive field, but responded only to strong mechanical stimuli applied to the periphery of the receptive field. In the center of the receptive field, tactile stimulation of a small restricted area was effective, and the tactile receptive field showed a somatotopic organization. The mandibular distribution was represented dorsomedially, the maxillary distribution next to that, and the ophthalmic distribution laterally. Furthermore, a rostrocaudal differentiation similar to that observed with tactile units in pars magnocellularis was found. Hence, a double somatotopic representation of tactile sensation within the caudal medulla oblongata was indicated.

1. Somatosensory afferent input and its relationship with efferent output were examined in the primary face motor cortex (MI) and adjacent cerebral cortical areas. Excitatory afferent inputs were tested in a total of 1,654 single neurons recorded in awake or anesthetized monkeys (Macaca fascicularis), and output was characterized in these same monkeys by the movement and EMG responses evoked by intracortical microstimulation (ICMS) at the neuronal recording sites. 2. Most neurons in the MI area responded to light tactile stimulation of the orofacial region, especially the upper lip, lower lip, and tongue. Although contralateral afferent inputs predominated, 21% of the neurons received ipsilateral or bilateral orofacial inputs. The afferent input evoked by tactile stimulation of the upper and lower lips was represented especially at the medial border and the input from the tongue at the lateral border of MI. However, in most regions of MI between the medial and lateral borders, an intermingling of tactile inputs from different orofacial areas occurred. Multiple representation of tactile input from the same orofacial area was found in several, often quite separate, intracortical sites in MI. 3. Only a small proportion of the MI neurons could be activated by the deep stimuli used (e.g., stretch and pressure applied to muscle, passive jaw movement, low-intensity stimulation of hypoglossal nerve) from the orofacial region. Those neurons which did respond to these low-threshold deep inputs were not clearly segregated from those which responded to tactile input, although most of the neurons receiving deep input were located in the rostral part of MI. 4. A somatotopic pattern of representation of orofacial tactile input was more obvious in the primary face somatosensory cortex (SI). At the medial border of SI, the periorbital area was represented, then followed laterally in sequence the tactile representation of the upper lip, lower lip, and intraoral area. Contralateral afferent inputs predominated, but as in MI, a considerable proportion of SI neurons received ipsilateral or bilateral orofacial inputs. Few neurons in the region explored (areas 3b, 1, and 2) responded to deep orofacial stimuli. 5. Tactile input also dominated the input patterns of neurons in the premotor cortex (PM). Most neurons received ipsilateral or bilateral orofacial afferent inputs and no clear somatotopic pattern was noted. Several PM neurons were also activated by visual stimuli. 6. Muscle twitches evoked by ICMS were limited to MI.(ABSTRACT TRUNCATED AT 400 WORDS)

The activity of 134 cold fibers innervating the hairy skin of the face was recorded from fine dissected strands of the infraorbital nerve in rhesus monkeys anesthetized with sodium pentobarbital. A precisely controlled contact thermode was used to produce rapid temperature shifts of approximately 10 degrees C/s in the cooling and warming directions with a 20-60 degrees C range. Cold fiber receptive fields usually were single spots less than 300 mum in diameter. The mean conduction velocity of 94 cold fibers determined by electrical stimulation of the receptive field was 9.0 m/s, with a range indicating an almost exclusive A-delta population. Rapid cooling shifts of 1-10 degrees C produced an initial transient period of high-frequency discharges, which decayed rapidly and was followed by a period of slow adaptation. Intensity functions were linear for cooling shifts up to 6-8 degrees C, and the slope of the intensity function was independent on the base-line temperature over a 30-40 degree C range. Rapid warming shifts produced a transient suppression of cold fiber activity. Previous cooling stimuli also influenced cold fiber responses, and these effects were dependent on the intensity of the previous stimulus as well as the stimulus interval. The average maximum discharge frequency of cold fibers to constant or steady-strate temperatures occurred at 30 degrees C, but varied over a 20-35 degrees C range for individual fibers. Periodic burst discharges separated by silent periods were present at steady-state temperatures of 20-35 degrees C.