Search

A variety of experimental evidence has implicated the mesencephalic raphe complex of nuclei and the locus coeruleus in the regulation of slow-wave sleep and REM sleep, respectively, and in the maintenance of diencephalic and telencephalic levels of serotonin and norepinephrine. The present study defines further the critical loci subserving brain stem control of fore-brain monoamine levels and electrographic indicators of these two states of sleep. After baseline sleep profiles were determined, lesions were placed in the dorsal and ventral tegmentum of the medbrain in cats. Following these lesions, fluorometric assay of various brain regions revealed widespread depletion of serotonin and norepinephrine although few differences in the pattern of regional reduction of monoamines were noted between the cats with dorsal and ventral tegmental lesions. However, comparison of sleep-waking profiles of the animals taken 2 wk after the lesion with profiles taken before yielded no consistent alterations in waking, slow-wave sleep of REM sleep. These results indicate no clear-cut correlation between regional levels of brain amines and sleep-waking profiles.

Changes in extracellular potassium concentration [K + ] were measured in the cat lateral geniculate nucleus (LGN) after electrical stimulation of the mesencephalic reticular formation (MRF), the visual cortex (VC) and the optic chiasm (OX) and after light stimulation of the retina. [K + ] was measured with a double barreled microelectrode. One barrel served as reference electrode to subtract local field potentials. The other barrel was filled with a K + selective ion exchanger and served as K + sensitive electrode. Parallel to the measurements of [K + ], excitability tests of optic tract (OT) fibers were performed. MRF, VC, OX and light stimulation cause a transient increase of K + in the LGN probably as a result of increased neuronal activity. The increase of K + has a similar latency, time course and cumulative property as the excitability change of OT terminals. Intracellularly recorded relay cells show a slowly rising depolarization after MRF stimulation. This depolarization has a time course similar to that of the excitability increase of OT terminals. It is suggested, that the depolarization of OT terminals after stimulation of the MRF, the VC and the OX is because of an increase of extracellular K + . It is proposed that axonal depolarization need not necessarily be associated with presynaptic inhibition by axo-axonic synapses.

Synaptic relationships between neuronal processes have been studied in thick sections (up to 1.0 mum) with high voltage electron microscopy. Some of the problems that arise in the study of such thick sections have been considered. (1) Where two parts of a single process are in continuity through a narrow stalk, as a dendritic stem and one of its spines, the continuity can generally not be seen if the stalk is included within the section or is crossed in the section by other processes. (2) Membranes that are viewed face-on cannot be seen in the thick sections and, therefore, processes belonging to two separate nerve cells may appear as though they are in cytoplasmic continuity. (3) Synaptic junctions that are viewed face-on cannot be seen in the thick sections, and junctions lying close to the same angle are also invisible; the relative number of invisible junctions depends upon a number of factors, including the section thickness and the size and contrast properties of the junctional specializations. Two methods of marking neuronal processes have been explored: (1) degenerating axons that are undergoing the dark degenerative change can be recognized readily within the thick sections. However, they stand out less clearly than in thin sections. (2) Neuronal processes that have been impregnated by an extra-rapid modification of the Golgi method can be easily traced in thick sections. It is possible to study some of the synaptic contacts made by these impregnated processes, especially if the processes have been only lightly impregnated or if the silver dichromate deposits are secondarily removed.

l - and d -glutamate, l - and d -aspartate, l - and d -cysteate, l -cysteine sulphinate, and to a considerably lesser extent (if at all), N-acetyl- l -aspartate, excite lateral geniculo-cortical relay cells. 5-Hydroxytryptamine (5-HT) blocks the spontaneous and synaptic firing of lateral geniculate nucleus (LGN) neurones evoked by photic stimulation in concentrations that have little or no effect on the actions of these excitatory amino acids. If this effect of 5-HT reflects postsynaptic antagonism of the optic nerve transmitter on LGN neurones, none of these excitatory amino acids is likely to be the transmitter released from optic nerve terminals. This is supported by the findings that 1-hydroxy-3-aminopyrrolidone-2 (HAP) and l -glutamate diethyl ester (two antaonists of glutamate-like compounds in the central nervous system) are ineffective or far less effective than 5-HT as depressants of the orthodromic firing of LGN neurones. Although it has been reported that the optic nerve of the rabbit contains relatively high levels of ergothioneine, ergothioneine is unlikely to be the transmitter released from optic nerve terminals onto LGN neurones, as it has no clear excitant action on lateral geniculo-cortical relay cells. In the medial geniculate nucleus (MGN). 5-HT does not have selective, dose-dependent depressant actions on the different forms of excitation, but probably depresses firing exclusively by a postsynaptic mechanism of action. The excitatory transmitter released from auditory afferent fibers onto MGN neurones and that released from medial lemniscal fibres onto relay cells of the ventrobasal thalamus is/are different from the optic nerve transmitter operating on LGN neurones.

A general account is given of synaptic organization in the rat LGd, with special emphasis on the intrinsic neurons, and the vesicle-containing P-boutons to which they give rise. The account is based on ultrastructural studies of normal adult rats, and of experimental animals surviving from less than one day to more than four weeks following unilateral eye removal or ablation of the visual and peri-visual cortex. P-boutons originate as narrow stalks or as blunt outpushings from presynaptic dendritic shafts. Commonly a single appendage comprises a series of P-boutons interconnected by narrow intervaricose portions. There is a very close correspondence in size and appearance between such appendages characterized by electron microscopy and the complex dendritic appendages seen in Golgi impregnations. P-boutons represent the principal synaptic territory of the intrinsic neuron. They arepresynaptic to relay cell dendrites (or dendritic appendages), and to other P-boutons (or, less commonly, to presynaptic dendrites). They arepostsynaptic to other P-boutons (or, less commonly, to presynaptic dendrites), to axon terminals containing ‘flattened’ vesicles (F-boutons), and to large intraglomerular axon terminals containing spherical synaptic vesicles (R-boutons). Degeneration of R-boutons after enucleation indicates that most are the terminals of retinal afferents. The P-boutons are intermediate elements in various serial synapses, the most characteristic of which is the intraglomerular triplet (or triad) synapse. At triplet synapses, a P-bouton and a relay cell dendrite onto which the P-bouton synapses, both receive at least one synaptic contact from an R-bouton. The possible role of triplet synapses in rapid feed-forward inhibition is considered. P-boutons and presynaptic dendrites also establish reciprocal synaptic relationship with one another, although closely spaced reciprocal synapses (c. 0.25 μm apart) are rare. The F-bouton population originates at least in part from small myelinated axons. The F-boutons contain closely packed, cylindrical synaptic vesicles, establish Gray type 2 contacts and are never postsynaptic. They are greatly outnumbered by P-boutons within the glomeruli, but synapse extensively in the extraglomerular neuropil onto both intrinsic and relay cell somas and dendrites, and onto the initial axons of relay cells. The possibility that some F-boutons originate from brain stem afferents is considered.

The use of retrograde axonal horseradish peroxidase (HRP) transport in determining cells of origin of central fiber systems has been explored in young and adult rats by injecting HRP in different portions of the forebrain. After HRP injection in different cortical areas, HRP reaction granules were found in the neuronal cell bodies of the corresponding thalamic nuclei, while after injection into the caudate putamen HRP-positive granules were found also in the cell bodies of the parafascicular nucleus and the substantia nigra. It is concluded that the HRP injection method represents a promising technique for determining remote cells of origin of fiber systems in brains of young and adult rats and that it produces especially striking results when the material is examined under dark field illumination.

Learning of brightness and pattern discrimination in normal rabbits and in rabbits with striate and occipital lesions was compared. Those with striate lesions did not differ from normal rabbits in learning brightness discriminations but took significantly longer to learn patterns consisting of striations differing by 90° and 45°. No rabbit with striate lesions learned to discriminate either striations differing by 22° or a cross/ circle discrimination. Those with occipital lesions did not differ from normal rabbits in learning brightness or pattern discriminations. The relationship between receptive field characteristics of neurons in striate cortex and the effects of striate lesions on visual discrimination is discussed.

Electron microscopic examination of the lateral geniculate nucleus in monkeys reveals the consistent occurrence of triadic synaptic arrangements where a retinal axon terminal is presynaptic to both a principal cell (P-cell) and a non-axonal portion of an interneuron (I-cell) containing flattened vesicles, which in turn is presynaptic to the same P-cell element. These ‘triads’ are found within glomeruli where the P-cell participates with a dendritic protrusion and the I-cell with a dendritic appendage (type 1 triad), and also outside the glomerulus where the P-cell is represented by its soma or very proximal dendrite (type 2 triad), or the I-cell profile is the soma which again contains synaptic vesicles (type 3 triad). The most parsimonious interpretation of the functional significance of the triadic synapse is to consider it as a device for the inhibitory phasing of the P-cell discharge resulting from the release of I-cell inhibitory transmitter by excitation of the interneuron through the same retinal afferent which causes the initial tonic activity of the P-cell. Further roles of the I-cell are discussed on the basic of a model which considers a random geometry of dendritic (long) and axonal (short) arborizations. The model suggests 3 possible I-cell actions: (1) local inhibition limited to the triadic arrangement; (2) inhibition at a distance through an axonal mechanism; and (3) inhibition at a distance by way of the presynaptic dendrites.

The retinogeniculate pathways of several different genotypes of mink have been studied by the Nauta and Fink-Heimer methods. An abnormal retinogeniculate pathway has been found in all mink in which the retinal pigment is reduced. Most of the abnormally routed nerve fibers arise in the temporal retina and cross in the chiasm, instead of staying ipsilateral as is normal. Some abnormal fibers in some of the mink also appear to arise in the nasal retina close to the line of decussation, and these pass ipsilaterally instead of following their normal crossed pathway. A lack of pigment in the coat is not by itself associated with a pathway abnormality. In general, the size of the abnormal fiber component is related to the severity of the retinal pigment deficit. The abnormality is not related specifically to one gene or gene combination. We have found eight different gene combinations which produce a reduction of retinal pigment associated with a pathway abnormality.

Autonomic blockades were used to examine relationships between heart rate conditioned responses (CRs) and unconditioned responses (URs) during differential classical conditioning in rabbits. Electrical stimulation of septal region or hypothalamus through chronically implanted electrodes was the unconditioned stimulus (US); conditioned stimuli (CSs) were intracranial stimulation of left and right lateral geniculate nuclei. Cholinergic blockade by atropine methylnitrate abolished bradycardia URs and CRs; whereas, beta-adrenergic blockade by propranolol did not diminish these responses. This indicates that autonomic mediation of the bradycardia responses consisted of increases in vagal tone. Alpha-adrenergic blockade by phentolamine abolished bradycardia URs, but not CRs, indicating that different central mechanisms mediated these responses. In a second experiment, one group of rabbits was injected with saline and another group was injected with phentolamine before each of six acquisition sessions. Both groups developed bradycardia CRs although phentolamine abolished the blood pressure URs and converted the cardiodecelerative UR to cardioacceleration.

The nictitating membrane response of rabbits was conditioned to brain stimulation (15 pps) and acoustic clicks (25 Hz). With electrode tips located in medial geniculate bodies, a summated generalization gradient with a peak at 20 Hz was obtained when animals were tested in extinction to various frequencies of acoustic clicks ranging from 5–35 Hz. By contrast, animals with electrode tips located in nonauditory structures (optic tract, lateral geniculate nuclei, reticular formation) produced generalization gradients resembling those obtained from animals conditioned only to the 25-Hz click train.

The retina maps over the dorsolateral and posterior surfaces of the contralateral dorsal lateral geniculate nucleus of albino and pigmented rats, such that the upper retina projects posteriorly and the lower retina projects over the dorsolateral surface. Nasal retina projects ventrolaterally and temporal retina dorsomedially. From the surface, lines of projection (demonstrated after either localised retinal or visual cortical lesions) tend to run deep and anteriorly within the nucleus. The area covered by the uncrossed optic pathway differs between pigmented and albino rats. In the pigmented animals it extends no more than 60° from the edge of the visual field represented in the crossed projection, while in albino animals it extends as far as 100° or more. The uncrossed projection in the albino strains tends to be deficient posteriorly (upper retinal representation) and dorsomedially, and the overall density is less than that found in the pigmented animals. Small lesions localised in the extreme peripheral temporal retina of both albino and pigmented rats have always produced degeneration in the contralateral as well as ipsilateral geniculate, even though some of the lesions map only as far as, or within the peripheral 20° on the contralateral colliculus. Most of these lesions in the albino rats give two patches of uncrossed degeneration in the geniculate with at least one focus of degeneration in the contralateral geniculate. Those made in the lower temporal retina of the albino rat give in addition to the uncrossed patches, two areas of crossed degeneration in the geniculate separated by about 50° in terms of visual field projection. These double projection aberrations do not occur in pigmented animals. The suggestion is offered that in albino rats the retina of each eye maps totally on the contralateral lateral geniculate nucleus. However, the vertical midline of the visual field is represented at about 40–50° from the medial edge of the nucleus. A normal (but sparse) uncrossed pathway maps lateral to this position, but also maps in duplicate medial to it. In addition, it appears that some crossed axons may also be abnormal in their termination, and project to both sides of the vertical meridian. If the above interpretation is correct, the anomalies of the albino rat may derive from a confusion of attempting both field and retinotopic maps on the same nucleus. The possibility exists that a comparable total crossed retinogeniculate projection exists in pigmented animals but that the retina temporal to the vertical midline projection is restricted in its connection to a small band on the medial border of the contralateral nucleus.

This paper describes an optic stimulator suitable for mapping visual receptive fields of single neurons. This stimulator allows the presentation of stationary stimuli with different forms and orientation and of stimuli moving at different velocities along all possible directions in the visual field.

Cats were raised with one eye sutured and with a lesion in the retina of the other eye. In these cats the competitive interaction between the pathways that go to the cortex from each eye was tested by studying the behavioral capacities, the electrophysiological responses and the morphological appearance of the geniculo-cortical pathways. Two parts of the visual system in which no binocular competition was possible were defined. One is the segment that receives inputs from the monocular crescent of the visual field, which has been called the monocular segment. The other is the artificial monocular segment created by the limited lesion of the non-deprived retina, and this has been called the critical segment. In the binocular segments of the visual pathways we found, as have others, that: (1) behaviorally, cats do not respond to objects viewed by the deprived eye; (2) cortical cells tend not to respond to stimulation of the deprived eye; and (3) geniculate cells innervated by the deprived eye grow less than the normally innervated cells. However, we found that the deprived eye is more effective in driving neurons in contralateral than in ipsilateral cortex. Within the monocular and the critical segments of the visual pathways we found: (1) that cats orient appropriately to visual stimulation of the deprived eye, (2) that cortical cells respond to visual stimulation of the deprived eye, and (3) that geniculate cells grow more than the deprived cells in the binocular segment of the nucleus. Thus, the deleterious effects of visual deprivation of one eye can, to some extent, be prevented by damage to the other.

Single catecholamine-containing neurons in the dorso-lateral pontine tegmentum were recorded in unanesthetized, freely behaving cats. Microscopic lesions were made on each recorded unit and subsequently identified for catecholamines by fluorescence histochemical analysis. The majority of the NE-containing neurons exhibited low spontaneous discharge rates in quiet wakefulness and in slow wave sleep. In paradoxical sleep, the medially located NE-containing neurons tend to exhibit ursting discharges which are closely related to individual PGO waves. The laterally or dorsally situated NE units fire more slowly and tend to derease their firing activity during paradoxical sleep. Tonically active, relatively fast NE-containing units were also found. Often, those neurons showed greatly increased activity before the cat awoke from either slow wave sleep or paradoxical sleep, with activity persisting during the early moments of waking. The combination of histochemical and electrophysiologic methods proved essential for correlating neurochemistry and function within the heterogeneous NE-containing nuclei of the cat pons.

Injections of small quantities of tritiated amino acid were made in the dorsal lateral geniculate nucleus (LGNd) and the adjacent posterior nucleus (PN), and the cortical projections of these nuclei were studied using the autoradiographic tracing method. It was concluded that the laminar division of LGNd projects only to areas 17 and 18 of the ipsilateral hemisphere. That portion of LGNd designated the medial interlaminar nucleus (MIN) projects to areas 18, 19 and the Clare—Bishop are (CB). PN was found to project to areas 19, CB, and a region within the splenial sulcus. No subcortical projections of LGNd or PN were observed. The distribution of transported label within cortical laminae showed that terminations occur largely in layer IV of all cortical areas studied, and that a relatively small number of terminations take place in layers I–III and in layer V. The cortical labeling pattern in areas 17 and 18 indicated that a substantial number of terminations may also exist in layer VI. The initial trajectory of PN and MIN axons was studied. PN fibers coursed laterally and remained closely applied to the dorsal border of LGNd before turning dorsally into the visual radiations. Most MIN fibers, on the other hand, passed laterally through the laminae of LGNd before ascending to the cortex.

Lesions were made in the visual system in a series of kittens, and fiber degeneration stained by the Eager or Fink-Heimer methods. Stereotaxic lesions made in the lateral geniculate nucleus (LGN) in one day old kittens led to the appearance of finely dotted fiber degenerationn in area 17 (concentrated in layer IV) two days later. Thalamic lesions involving the LGN in older kittens caused fiber degeneration in the other visual areas. This was first seen in the lateral suprasylvian gyrus (SSG) at six days, in area 19 at 14 days, and in area 18 at 21 days. Lesions of visual cortex affecting areas 17 and 18 caused degeneration of descending connections to the LGN, lateralis posterior and superior colliculus when made in kittens one day old. However, ipsilateral cortical connections to area 19 were not seen until the kittens were 19 days old at operation, and connections to the suprasylvian gyrus appeared at 21 days. Contralateral cortical connections carried by the corpus callosum were not seen until the kittens were 26 days old at operation, and a distribution of degeneration comparable with that seen in adults was present at 40 days. This time sequence of development is discussed in relation to what is known about the time of development of functioning in the cat's visual system.

The laminar structure of the dorsal lateral geniculate nucleus was studied in carnivores of the weasel, raccoon and fox families. All have the same basic pattern of laminar organization in their lateral geniculate nuclei. Laminae A and C receive a contralateral projection from the retina and laminae A1 and C1 receive an ipsilateral projection. It is not known whether lamina C2 receives a retinal projection. There are some variations to the basic pattern of laminar organization. Thus, in the mink and weasel laminae A and A1 are each subdivided into a pair of separate but similar leaflets. In the ferret and coatimundi these laminae are only partly subdivided. In the skunk, raccoon, ringtailed cat and fox there is only one lamina A and one lamina A1 in each lateral geniculate nucleus. There is some variation of the C laminae also. The C laminae are best displayed in the fox, where all three laminae — C, C1 and C2 — can be recognized in Nissl sections. In other carnivores, for example the mink and ferret, the C laminae cannot be distinguished from each other in normal brains and are described on the basis of the degeneration that is seen in Nauta and Fink-Heimer sections after a unilateral enucleation. In the raccoon lamina C can be identified but lamina C1 may be missing. The perigeniculate nucleus is variable in structure in carnivores. In the weasel and raccoon family the perigeniculate nucleus is a thick layer containing many large cells while in the cat and fox, it is a thin and rather diffuse group of cells. The perigeniculate nucleus may receive a direct retinal projection but if so, it is only a very sparse one.

Rabbits received Pavlovian conditioned inhibition training (nictitating membrane response) using ESB as the reinforced CS and a tone as the conditioned inhibitor. Summation, retardation, and generalization tests indicated that the use of ESB in the paradigm did not interfere with the development of inhibitory control by the tone.

After introduction of small amounts of horseradish peroxidase (HRP) into known visual centers of the brain, retinal ganglion cells projecting to these regions were detected by the accumulation of HRP-positive granules in their somata. Control experiments indicated that the HRP-positive granules had reached the ganglion cell somata by retrograde axonal transport, and did not represent blood-borne or endogenous peroxidase. Using this technique, it has been determined that axons of both large and medium-sized neurons in the ganglion cell layer of adult and immature rat retinae terminate in the superior colliculus and lateral geniculate body, and that characteristic displaced ganglion cells with axonal connections to these visual centers occur regularly in these retinae. In addition, certain small cells in the retinal ganglion cell layer are described which may represent glia or interneurons, or ganglion cells which lack the ability to transport peroxidase or which lack central connections to these visual centers of the brain.

Morphological and electrophysiological techniques were applied to obtain quantitative data about the degeneration of optic tract synapses in the lateral geniculate nucleus of the cat. The various morphological changes during degeneration are closely correlated to the changes found in the electrophysiology of synaptic signal transmission. The findings can be interpreted by application of the vesicle hypothesis of synaptic transmission.

In patients undergoing thalamotomy for intractable pain, multi-contact platinum electrodes were stereotaxically implanted so that the striate cortex and geniculocalcarine tract could be stimulated to evaluate the feasibility of a visual prosthesis. The parameters of stimulation were 50–300 Hz, 0.1–1 msec pulse duration and 0.1–5 mA/phase. Phosphenes were evoked in 7 out of the 17 cases studied. The projection in space of the phosphene depended upon the site of stimulation. The configuration, color and brightness of the phosphene varied from a simple white or colored light to occasionally a multicolored complex pattern. Some phosphenes appeared to blink or flutter, some were stable in position, others appeared to move away radially from the fixation point. Histological studies on 6 of the brains suggested that the phosphenes were more often evoked from the striate cortex than from the geniculocalcarine fibers.

Much work has related limbic structure with hypothalamic function rather than with higher nervous system function. Most studies have dealt with single limbic structures rather than with several as interrelated functional systems. Upon consideration of the total limbic-structure complex it would appear that the septum-hippocampus-amygdala form an interface between the isocortex and the thalamus. Our work relating to projections of the limbic system, especially the septal area, has directed our attention to the thalamus as a particularly important target of limbic system projections. Furthermore, our work on projections of the cingulate gyrus reveals that this cortical area projects strongly to other cortical regions as well as to thalamic nuclei. The orbital frontal cortex, cingulate gyrus, and hippocampal gyrus are isocortical areas which then link the limbic system with other corticothalamic systems. This feature, plus strong thalamic connections from the hippocampus, septum, and amygdala provide a basis for considering the limbic system as an interface between the overlying cerebral isocortex and thalamic structures. This interface may be a key integrating system related to selective modulation of emotion and sensory mechanisms of the brain via a number of feedback circuits wherein recycling could be effected through the temporal and/or the frontal cortex.

In the past few years the technique of mapping pathways in the central nervous system by anterograde axoplasmic transport of radioactive molecules has come into wide use and is now an important supplement to Nauta degeneration methods e,6,1°,13. Several investigatorsa,3,v,9,12 have noted radioactive substances in the postsynaptic ceils, which suggests that these cells take up labeled material released from the terminals 1,3,7. Grafstein 4 was the first to explore the possibility of tracing a pathway beyond the terminals of the initially labeled cells, by examining also the projections of the recipient postsynaptic neurons. By radiochemical measurements and by autoradiography, it was shown that after injection of [3H]proline and [aH]fucose into one eye of a mouse the contralateral striate cortex was more heavily labeled than the ipsilateral, and that the label was concentrated in layer IV 5,14. In the macaque monkey the geniculostriate pathway terminates in a very dense, highly localized manner, mainly in layer IV C. Furthermore, projections from the 2 eyes end in a characteristic alternating stripe-like pattern of oculardominance columns s. It occurred to us that if radioactive substances were transported transneuronally, injection of labeled material into one eye followed by autoradiography of the cortex might reveal the entire system of ocular-dominance columns. For the autoradiographic study of transneuronal transport in the primate visual system, 50/~1 of a saline solution containing L-[6-3H]fucose (2.5 mCi/ml, 13.4Ci/ mmole) and L-[3H]proline (7.5 mCi/ml, generally labeled, 6.8 Ci/mmole) was injected into the vitreous of the left eye ofa 3 kg normal Rhesus macaque. This injection was repeated 5 times at 12 h intervals (total dose 3.0 mCi). The animal was perfused with 10 ~ formalin 3 weeks after the initial injection. The lateral geniculate nucleus was cut into 20 #m frozen sections, and the striate cortex was embedded in paraffin and cut into 15/~m sections. The sections were coated with Ilford K5 emulsion, left in the dark for 2-4 months and developed in Dektol. Sections were counter-stained with thionin. In the lateral geniculate nucleus all layers receiving projections from the injected eye were strongly labeled (Fig. l A and B). The other layers showed grain counts higher than background, perhaps partly because of fibers of passage from the retina

1.1. The dog's alpha rhythm recorded from cortex and thalamus has been analysed quantitatively by means of spectral analysis and shown to provide a good model of that of man. 2.2. The hypothesis that cortical alpha rhythms are paced by thalamic generators has been tested, particularly by studying the relationships between alpha rhythms recorded in the lateral geniculate nucleus and visual cortex, areas where alpha activity predominated. 3.3. The strength of thalamo-cortical relationships has been measured by means of coherence functions and treated statistically. 4.4. Significant (P 0.75) corticocortical coherences were found over relatively large areas the diameter of which was often 5 or 6 mm. 5.5. On the basis of these findings the deterministic pacemaker concept of thalamo-cortical regulation of alpha rhythms was criticized and an alternative stochastic model was proposed. 6.6. In this model thalamic and cortical alpha rhythms would result from the filter properties of neural networks when submitted to several random inputs. Neural networks with similar design and frequency selectively should exist in different inputs. Neural networks with similar design brain areas where they would give rise to alpha rhythms with the same frequency spectra. The degree of coherence between different areas would depend upon the correlation of the inputs with the different networks. The apparently simultaneous occurrence of bursts of alpha rhythm at different locations would depend on a common modulating influence which would gate the "alpha filters" at the same time.

In albino mammals, the absence of pigmentation in the eye is associated with abnormalities of the visual pathway and these result in a scrambled input to the visual centres of the brain. Recent research on Siamese cats, in which more than one pattern of abnormality has been found, shows that there are several ways in which the cortex can deal with the abnormal input, and is beginning to define the rules according to which the cortex selects its inputs.

Cats were conditioned to press a bar for food reward with repetitive stimulation of the lateral geniculate nucleus. The stimulation served both as a discriminative stimulus to generate the bar-press and to elicit a series of evoked responses in the visual cortex. With well-trained cats, we recorded evoked responses at the initiation of the bar-press. Each of the responses consisted of positive-negative diphasic waves of about 10 msec duration. The positive wave had small positive deflections on its rising phase. On repetitive stimulation, those waves were small at the beginning, then augmented and reached maximal amplitude. Bar-press occurred several tenths of a second after the maximum enhancement. Large augmentation of the response occurred when the first response was small and vice versa. We also found that single shock stimulation to the geniculate could serve as a discriminative stimulus for initiation of bar-pressing.

The spatial and temporal distribution of optic fiber degeneration was studied with three selective silver methods in cats which sustained unilateral optic nerve transection 2 days to 15 mo before death. At the second postoperative day, only traumatic disintegration was discernible. Starting with the fourth day, axonal degradation appeared in central portions of optic pathways and centers. Degeneration spread throughout the pathways at the seventh day and reached a plateau in 9–10 days postoperatively. No overt changes were noted in the subsequent 2 mo. From the third month on there was a gradual and even reduction in the amount of impregnated degeneration products, except for that in the dorsal lateral geniculate and superior colliculus which vanished sooner. With deterioration times of 6 mo or longer, only occasional scattered debris could be detected. There was no significant “late degeneration” to suggest the presence of centrifugal (efferent or retinopetal) optic fibers.

The efferent connections of the ventral lateral geniculate nucleus (LGNv) of the albino rat and the cat have been studied using the autoradiographic method for tracing axonal pathways. Following the injection of 3H-proline or 3H-leucine into the LGNv of the rat, label transported in the rapid phase of axonal flow was found bilaterally in the olivary pretectal nuclei, the lateral terminal nuclei of the accessory optic system, and the ventral portion of the suprachiasmatic nuclei of the hypothalamus, and ipsilaterally in the rostrolateral portion of the superior colliculus. Since these regions are known to receive a direct projection from the retina, comparisons have been made of the distribution of silver grains in autoradiographs of each region following injections of 3H-proline into the eye and into the LGNv; in every nuclear region except the superior colliculus the grain distributions were found to overlap precisely and, in the suprachiasmatic nuclei there also appears to be a similarity in the relative intensity of the input to the nuclei on the two sides. In the superior colliculus, the retinal fibers end mainly within the more superficial laminae, whereas those from the LGNv are distributed mainly to the deeper layers where they overlap the projection from the striate and peristriate cortex. The LGNv has also been found to project to the zona incerta on the same side and to the contralateral LGNv, In the cat a similar set of projections to the lateral terminal nuclei of the accessory optic tract, the suprachiasmatic nuclei, and the pretectal areas of both sides has been found, together with a projection to the ipsilateral superior colliculus and the zona incerta of both sides. No evidence could be found in either species for a projection from the LGNv to the visual cortex.

Cats were trained in a double-grill box to discriminate a change in the temporal pattern of ongoing vibrotactile pulses at two different intensities. Animals acquiring the discrimination were prepared with bilateral insular-temporal lesions. The temporal pattern discrimination was lost postoperatively, and could not be reestablished even after prolonged. A simple vibrotactile intensity discrimination could be learned postoperatively, indicating that the impairment on the temporal pattern task was not due to a general deficit in associative learning. Earlier research has been reported which implicates the insular-temporal region in visual temporal pattern discrimination. Considered in conjunction with this earlier work, the present data suggest that insular-temporal cortex is a multimodal area concerned with the perception of temporal patterns of stimuli.

In the adult cat, just before the onset of and throughout paradoxical sleep, sharp, monophasic waves appear in the pontine reticular formation, and are transmitted to the lateral geniculate nucleus and occipital cortex. This report describes a study of the appearance and maturation of these ponto-geniculo-occipital weves, or PGO “spikes,” in the lateral geniculate nucleus of the developing kitten. Thirty-nine implantations of the lateral geniculate nucleus were carried out in 34 kittens (ages 8–75 days). Electrodes were also placed for the recording of electrocorticograms, neck muscle activity, and eye movements. Despite the high proportion of paradoxical sleep, and the copious amount of peripheral phasic activity in the neonatal kitten, no PGO activity was found prior to Day 15. The average age of emergence of the activity was Day 21. The PGO waves, at initial appearance, were low in frequency as well as amplitude. However, during a 3- to 6-day sequence, the spikes increased in both frequency and amplitude, and an association developed progressively with the increasingly well-defined periods of paradoxical sleep. Adult PGO spike frequencies were reached by Day 35, though the temporal characteristics of their discharge continued to change for several weeks thereafter. The 3-week postbirth latency to the first appearance of the PGO spikes, as well as the ensuing rise in their recorded frequency and amplitude, seem to be basic characteristics of PGO development. Further, the ontogenesis of spontaneous PGO activity in the lateral geniculate nucleus of the kitten during paradoxical sleep parallels the pace of maturation of the sleep-wake pattern and of the neuroanatomical and neurochemical pathways that function in the mediation of the stages of sleep.

6-Hydroxy-DOPA (6-OH-DOPA) was used as a tool to map out central noradrenaline pathways in the mouse with the histochemical fluorescence method of Falck and Hillarp. After inhibition of the monoamine oxidase, 6-OH-DOPA treatment at a dose of 100 mg/kg, results in the appearance of strongly fluorescent, longish accumulations of endogenous noradrenaline within the nerve fibers, while the dopamine and 5-hydroxytryptamine neurons were unaffected. However, this specificity is not absolute, since a higher dose, 400 mg/kg of 6-OH-DOPA also affected the nigro-striatal DA neurons. Mainly the noradrenaline fibers from the locus coeruleus area were demonstrated and could be traced into the cortical areas of the telencephalon and cerebellum, the geniculate bodies, the thalamus, the lateral hypothalamic area and the rhombencephalon. The ventral noradrenaline bundle was not markedly affected by 6-OH-DOPA. The 6-OH-DOPA technique makes it possible to map out many noradrenaline pathways without disturbing their topographical pattern and also to study them in areas containing dopamine fibers.

1. 1. In chronically prepared cats, evoked potentials of the visual cortex (VC) to flash stimulation of the eye or electrical stimulation of the optic chiasm (OC) and optic radiation (OR), and those of the lateral geniculate body (LGB) to electrical stimulation of OC were recorded in parallel with spontaneous EEGs during and after hypoxia induced by inhalation of a hypoxic gas with oxygen tension of 18–20 mm Hg. 2. 2. After the onset of hypoxia, all electrical activity was transiently activated. Then it declined and finally disappeared. VC was affected earlier than LGB, and the postsynaptic activity disappeared earlier than the presynaptic activity, in LGB as well as in VC. 3. 3. The recovery of some evoked activities proceeded smoothly for the first 20 min but thereafter slowed down, and sometimes deterioration again took place. 4. 4. EEG activity first noted in the recovery course consisted of fast waves of very low amplitude. 5. 5. EEGs and evoked potentials recovered almost completely when resuscitation procedures were applied before presynaptic activity of VC disappeared. 6. 6. In half of the cats electrographic seizures were observed in the recovery course. In one group seizure discharges occurred early in the recovery course and continued for a short time: in the other group seizure discharges occurred very late and laster much longer. In the latter group a complete recovery from the hypoxic effects was rarely obtained. 7. 7. There were some cases in which the electrographic activities completely recovered from the hypoxic effects but behavior remained abnormal.