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The ability to sense humidity and wetness is an important sensory attribute for many species across the animal kingdom, including humans. Although this sensory ability plays an important role in many human physiological and behavioural functions, as humans largest sensory organ i.e. the skin seems not to be provided with specific receptors for the sensation of wetness (i.e. hygroreceptors), the neurophysiological mechanisms underlying this complex sensory experience are still poorly understood. The aim of this Thesis was to investigate the neurophysiological mechanisms underpinning humans remarkable ability to sense skin wetness despite the lack of specific skin hygroreceptors. It was hypothesised that humans could learn to perceive the wetness experienced when the skin is in contact with a wet surface or when sweat is produced through a complex multisensory integration of thermal (i.e. heat transfer) and tactile (i.e. mechanical pressure and friction) inputs generated by the interaction between skin, moisture and (if donned) clothing. Hence, as both thermal and tactile skin afferents could contribute significantly to drive the perception of skin wetness, their role in the peripheral and central sensory integration of skin wetness perception was investigated, both under conditions of skin s contact with an external (dry or wet) stimulus as well as during the active production of sweat. A series of experimental studies were performed, aiming to isolate the contribution of each sensory cue (i.e. thermal and tactile) to the perception of skin wetness during rest and exercise, as well as under different environmental conditions. It was found that it is not the contact of the skin with moisture per se, but rather the integration of particular sensory inputs which drives the perception of skin wetness during both the contact with an external (dry or wet) surface, as well as during the active production of sweat. The role of thermal (cold) afferents appears to be of a primary importance in driving the perception of skin wetness during the contact with an external stimulus. However, when thermal cues (e.g. evaporative cooling) are limited, individuals seem to rely more on tactile cues (i.e. stickiness and skin friction) to characterise their perception of skin wetness. The central integration of conscious coldness and mechanosensation, as sub-served by peripheral cutaneous A-nerve fibers, seems therefore the primary neural process underpinning humans ability to sense wetness. Interestingly, these mechanisms (i.e. integration of thermal and tactile sensory cues) appear to be remarkably consistent regardless of the modality for which skin wetness is experienced, i.e. whether due to passive contact with a wet stimulus or due to active production of sweat. The novelty of the findings included in this Thesis is that, for the first time, mechanistic evidence has been provided for the neurophysiological processes which underpin humans ability to sense wetness on their skin. Based on these findings, the first neurophysiological sensory model for human skin wetness perception has been developed. This model helps explain humans remarkable ability to sense warm, neutral and cold skin wetness.

In order to process information, neurons must connect together to form a neuronal circuit. The formation of neuronal circuits is dependent on synaptic activity through glutamate receptors and downstream molecules within the post-synaptic density (PSD). The pathways downstream of glutamate receptors play an important role in maintaining appropriate synapses and forming neural circuits; mutations in genes that encode PSD proteins disrupt these pathways and are associated with many forms of intellectual disability in humans (Grant 2012). The development of neuronal circuits relies on two key developmental events; neurons must first send out axons locally and to disparate brain regions and then, neurons must form connections with the dendrites of target neurons. The rodent trigeminal system is a neuronal circuit that processes somatosensory information from whiskers on the facepad via nuclei in the brainstem to the thalamus and ultimately the cerebral cortex. Brain regions that comprise the trigeminal system are organised in a manner that topographically recapitulates the whisker pattern; each whisker on the rodent facepad corresponds to a physiological and anatomical unit in the primary somatosensensory cortex (S1) called a barrel. This topographical organisation creates a pattern consisting of thalamocortical axons (TCA) clustered into distinct whisker-related bundles and layer IV spiny stellate cells which segregate around the outside of TCA bundles. Three different anatomical patterns can be identified within the mouse S1 by labelling the cell soma, axons or the extracellular matrix. This strict organisation makes the rodent S1 an excellent model for discerning the proteins involved in neural circuit formation, and by screening genetic mutants for S1 patterning defects the molecular pathway involved in setting up neuronal circuits can be elucidated. Furthermore an understanding of these pathways may provide insight into how neuronal networks are disrupted in human intellectual disability. In the first data chapter, the expression profile of three neurofilament subunits were characterised in order to develop a method of identifying anatomical defects in barrel morphology. The precise organisation of the rodent S1 can also be used as a method to identify the cellular localisation of neurofilament subunits ex vivo. Neurofilaments are polymers formed from three subunits identified by their relative molecular weight. By using the unique patterning of S1, each neurofilament subunit shows a unique spatialtemporal expression pattern in the somatosensory cortex. Two neurofilaments subunits; the medium and the heavy neurofilament subunits can be used to identify TCA which can be used as an indicator of anatomical defects in barrel patterning. In chapter 4 neurofilament labelling was used in conjunction with other histological techniques to investigate S1 organisation in mice lacking synapse associated protein 102 (SAP102). SAP102 is a PSD scaffolding molecule that binds to both NMDA receptor subunits and SynGAP, a synaptic GTPase activating protein, furthermore it is associated with X-linked mental retardation in humans (Tarpey et al., 2004; Zanni et al., 2010). Mutant mice lacking functional NMDA receptors or PSD proteins such as SynGAP show defects in S1 pattern formation (Barnett et al., 2006; Iwasato et al., 2000; Wijetunge, Till, Gillingwater, Ingham, & Kind, 2008). SAP102 null mutants (SAP102-/y) have defects in synaptic plasticity and are slow to learn on behavioural tasks (Cuthbert et al., 2007), however it is unclear how the loss of SAP102 may disrupt neural networks. SAP102-/y were found to have a reduction in brain mass compared to wild-type littermates, but cortical thickness and patterning of S1 is unchanged. SAP102-/y have fewer TCA reaching the cortex compared to littermates; furthermore SAP102-/y mutants have layer specific defects in the density of dendritic spines. These data suggest that in the absence of SAP102 connectivity in the S1 is altered by layer specific changes in synapses number and fewer axons innervating cortical layer IV. In the final experimental chapter (chapter 5) the combined role of SAP102 and Postsynaptic density protein 95 (PSD95) in S1 patterning was investigated. SAP102 and PSD95 are the main members of the membrane-associated guanylate kinase (MAGUK) family expressed during early cortical development. These proteins share a similar protein structure, perform similar functions at the synapse (Elias & Nicoll, 2007) and have been shown to compensate for each other in vitro (Elias, Elias, Apostolides, Kriegstein, & Nicoll, 2008). Genetic mutants lacking both SAP102 and PSD95 are not viable and do not survive beyond birth (Cuthbert et al., 2007; Petrie, 2008). Therefore in order to investigate the combined role of these proteins a novel approach was developed that utilises X-inactivation to produce mosaic animals containing cells that lack both proteins. The distribution of cells containing the same X-chromosome was investigated and found to be evenly distributed throughout the cortex, demonstrating that this method could be used to investigate allosomal genes. In mosaic animals where approximately half the cells only lack PSD95 and the remaining cells lack both SAP102 and PSD95, double knockout cells are viable and are equally represented in S1. These double knockout cells contribute to normally barrel formation which suggests that SAP102 and PSD95 are not required for barrel formation.

Development of the rodent somatosensory cortex is well characterised and involves activity-dependent mechanisms that occur during the first postnatal week. Glutamate is a key neurotransmitter responsible for signalling events that result in formation of cortical barrels - aggregates of cells in the cortex corresponding to whiskers on the face pad. The molecular mechanisms that occur downstream of glutamate signalling are not fully understood and data here contributes to the unveiling of some of these mechanisms. Transgenic mice with deletions of genes that encode members of the post-synaptic complex associated with NMDARs were used to understand the role of individual genes in the formation of barrels. SynGAP, a ras GTPase activating protein (GAP) that negatively regulates the ERK-MAPK pathway downstream of NMDARs is required for the formation of barrels and data here agrees with other findings that the ras GAP NF1 has a similar role. Examination of RICS, a RhoGAP and Dusp6 - a phosphatase that inactivates ERK reveals that neither are necessary for the formation of barrels. This finding adds to previous data postulating that barrels form in an ERK-independent manner (Watson et al., 2006, Barnett et al., 2006). MAGUKs are important scaffolding molecules in the PSD and bind NMDARs to downstream signalling molecules such as SynGAP. Two of these MAGUKs SAP102 and PSD-95 have roles in hippocampal plasticity, and learning and memory and Sap102 mutations result in a form of X-linked human retardation (Tarpey et al., 2004). Deletion of either gene does not cause defects in the development of barrels, perhaps due to compensation mechanisms already described in hippocampus (Vickers et al., 2006 Cuthbert et al., 2007). Double knockout mice die by P3 and analysis of all other mutants revealed a defect in the formation of barrels and segregation of TCAs in Sap102-/y Psd-95+/-. Surprisingly this defect was not seen in Sap102+/- Psd-95-/- mice, agreeing with previous findings that SAP102 is better able to compensate for loss of PSD-95 (is up-regulated) than PSD-95 is for SAP102. An explanation for this effect may lie with the fact that Sap102 is X-linked and therefore females that are heterozygote for Sap102 are mosaic with a population of cells expressing SAP102 and a population not expressing SAP102. Using β-Galactosidase antibody to label one population of cells, female mice that had two populations of cells were examined. In these mice one population of cells were Sap102-Psd-95+/-, and did not previously segregate into normal barrels and the other population were Sap102+Psd-95+/- and should segregate normally. Both populations of cells segregated normally, indicating that the cells expressing SAP102 were rescuing the cells not expressing SAP102 by a cell non-autonomous mechanism. The final part of this thesis focuses on the role of glutamate-dependent signalling pathways in the regulation of CSPGs- key extracellular matrix proteoglycans that regulate the termination of the sensitive period. Analysis of 3 overlapping but distinct subsets of chondroitin-sulphate proteoglycans (CSPGs) reveals that expression of each of the three is different throughout development. After 2-3 weeks perineuronal nets (PNNs) labelled with Cat-315 and Cat-316 are visible and locate to specific regions within the cortical barrel-field. To determine whether the formation of PNNs is regulated by proteins involved in glutamate signalling, expression of the three CSPG subsets was analysed in mice with barrel defects due to mutations of Plcβ1, Mglur5, Syngap and Prkar2b. Interestingly, Prkar2b mutant adults but no other mutants have reduced Cat-315-PNNs, indicating that PKARIIβ regulates pathways that lead to formation of Cat-315-PNNs in adulthood. Cat-315 has previously been found to be regulated in the cortex of visually deprived cats and the cortex of whisker-trimmed mice, indicating that specific subsets of CSPGs are regulated by neuronal activity. Molecular pathways that lead to expression of Cat-315 positive PNNs involve PKARIIβ and the formation of PNNs may be an important step in the plasticity of circuits in barrels. Taken together, these results demonstrate that an important part of molecular signalling downstream of glutamate enabling barrels to form is played by molecules that maintain structure inside the synapse and outside the cell.

Functional MRI was used to detect brain activations in the primary somatosensory cortex (SI) in response to a vibrotactile stimulus applied to the thumb (D1) and little finger (D5) of the right (R) and left (L) hands. Four studies were carried out with healthy subjects in order to determine the scanning and stimulation protocols that resulted in consistent and robust SI activity. It was found that a strong stimulus, compared to a weak stimulus, led to the SI activity being detected more frequently and at a more statistically significant level. Also, extending the scanning duration per digit further increased the T-scores. The SI activations for each digit showed multiple foci and were distributed throughout the SI area. However, a clustering occurred in separate centres for stimulation to RD1 and RD5 near the Brodmann area 1/Brodmann area 3 boundary. The Euclidean separations of the cortical digit representations for LD1-D5 and RD1-D5 were calculated on the basis of the `centre of mass' of the multiple activations. Observed separations ranged between 1.2 mm to 22.8 mm. A further vibrotactile fMRI study was carried out involving patients with complex regional pain syndrome (CRPS). It has been suggested an altered central processing mechanism is involved in the disease, possibly due to cortical reorganisation in the sensory/motor cortices. The most efficient experimental protocols from the healthy subject studies were used to determine if these cortical differences were present in four patients. Data were acquired over two scanning sessions, approximately four months apart. The study revealed multiple SI foci and overlapping between the digits in both the healthy and CRPS hands, similar to those observed in the first studies. Larger SI activations were detected in one patient, smaller SI activations were detected in another patient and two patients demonstrated cluster sizes in the normal range. The cluster sizes and the changes in size between the two scans suggest a correlation with the amount of pain experienced by the patients. A general lack of consistency in the results from all the studies may be attributed to the difficulty of reliably detecting SI activity at a field strength of 1.5 T.

The population of aging adults is rapidly increasing worldwide. Inequity in mobility independence alongside increasing disability incidence during aging reduce quality of life and participation- which are critical as the desire and need to work into older age rises. Manual wheelchairs (MW) have become increasingly relied upon by aging adults to support mobility loss. Therefore, in order to support safe and equitable MW use within the aging population, there is a need to design effective and practical environment-based interventions that are applicable to a large range of manual wheelchair users (MWUs). This dissertation applied a novel integration of human factors engineering and motor control theories to improve mobility task-environments and the corresponding design/evaluation process to better include the needs of aging MWUs. In doing so, MW incidence period and simulated impairment (SI) were also distinguished to investigate the usefulness and validity, respectively, within research and design. Our findings show that interventions of simple, augmented visuospatial information within path-following environments successfully facilitated underlying somatoperception and somatorepresentation processes for MWUs. Specifically, the top-down intervention improved MWU ability to align their assumed frustration with their perceived frustration associated with a movement task (from 80% difference in Baseline to 29% with the intervention), which is necessary to promote confidence and reduce self-limited participation. Bottom-up interventions improved the congruency between participants’ perception of performance and the objective measure of movement accuracy (e.g., collisions committed) was improved as high as 28% (percent increase; resulting in correlation up to r = 0.88 among MWUs) by the BU interventions. in addition, MWUs with later-in-life incidence no longer committed more collisions than those with earlier-in-life incidence (LL: 1.22(1.81) collisions in the 6m straight line displacement; EL: 0.57 (0.12)) in the presence of both top-down (LL: 0.66(1.11); EL: 0.33(0.49)) and bottom-up interventions (LL: 0.44(0.89); EL: No collisions observed). Further, this work revealed the invalidity/bias of using SI in both research and design endeavors, as the space required to perform a common maneuvering task was significantly less for the SI (7.0cm, CI95: 0.8) than the MWUs (8.9cm, CI95: 2.2). SI participants also commented on very different themes than the MWUs (“a fun experience” vs. “reminders of stressful situations faced in daily life”, respectively), highlighting differences in somatorepresentations and relevant task stressors between the two groups. In sum, this dissertation showcased how concepts borrowed from motor control theory offers new and attractive perspectives for human factors and accessibility research. This work offers recommendations to design and assess inclusive environment-based, augmented visuospatial feedback interventions that effectively consider underlying sensorimotor processes and reveal simulation of impairment cannot be a surrogate to represent the reality of MWUs in research.

Dravet syndrome (DS) is an infantile epileptic encephalopathy that is caused by loss-of-function mutations in the SCN1A gene, which encodes the voltage-gated sodium channel, NaV1.1. Haploinsufficiency of NaV1.1 in DS patients leads to imbalanced excitability across brain circuits, resulting in a broad phenotypic profile including drug-resistant convulsive and non-convulsive (absence) seizures, cognitive impairment, ataxia, and sleep disruption. Dysfunction in the somatosensory corticothalamic (CT) circuit underlies several DS phenotypes including absence seizures and sleep disturbances. Yet, the precise mechanisms underlying somatosensory CT circuit dysfunction in DS remain unclear. Here, we sought to identify the cellular and synaptic mechanisms underlying somatosensory CT circuit dysfunction in a haploinsufficiency DS mouse model. This work reveals that NaV1.1 haploinsufficiency leads to cell-type-specific changes in the excitability of reticular thalamic (nRT), ventral posterolateral (VPL), and ventral posteromedial (VPM) neurons. Further, we identified alterations in both glutamatergic and GABAergic synaptic connectivity within the somatosensory CT circuit in DS mice. These findings introduce glutamatergic neuron dysfunction and synaptic alterations as novel disease mechanisms underlying thalamic circuit dysfunction in DS, providing new targets for therapeutic intervention. In addition, we reveal that VPL and VPM neurons exhibit distinct firing properties in a healthy CT circuit, suggesting they differentially contribute to circuit-wide function in health and dysfunction in disease.

Background: Robot-assisted rehabilitation movement training is becoming increasingly popular but produces variable benefits. A recent study showed that the benefits of robotic hand training after stroke decreased if participants could not accurately sense finger movement at baseline. In that study, finger proprioception was measured with a new test called the “Crisscross” test in which participants pushed a button when they thought their index and middle fingers were overlapped as a robot exoskeleton slowly moved their fingers past each other [5]. The goal of this project was to search for a neural correlate of proprioceptive processing during the Crisscross test. Since previous work found that proprioception influences Event Related Desynchronization (ERD) measured before hand movement, we hypothesized that ERD before the button pressing response during the Crisscross test would reflect proprioceptive error. Methods: Five healthy participants (4 male, 1 female, aged 22-66) had their right index and middle fingers randomly moved in crossing patterns by a robotic exoskeleton and were asked to press a button with their left hand when they believed their right fingers were perfectly aligned. We measured ERD using EEG electrodes over the motor area contralateral to the button pressing hand. Results: The magnitude of the ERD associated with the button press during the Crisscross test was weakly correlated with the size of the proprioceptive error on each trial for four participants. Conclusions: Although more evidence is needed, these results suggest the intriguing possibility that ERD may serve as a novel neural correlate of proprioceptive processing.

Brain-derived neurotrophic factor (BDNF) is a member of the neurotrophin family and is an important signaling molecule that plays a crucial role in the proper development and function of the central nervous system. A variety of studies have suggested BDNF meets the criteria necessary to modulate cortical reorganization, including a study that found its transcription and release to be activity-dependent. Horizontal synapses in the primary somatosensory area, S1, facilitate functional reorganization across topographical representations. However, the molecular contributors to reorganization are not known. Since BDNF is a known modulator of synaptic transmission, this dissertation focuses on the effects of BDNF on horizontal synapses in S1, hypothesizing that BDNF has the capacity to alter synaptic transmission at these synapses.ivIn chapter 1, we found that acute bath application of BDNF had an inhibitory effect on layer II/III local field potentials. The inhibitory effect of BDNF was found to be Trk dependent, as inhibiting protein kinase activity proved to prevent BDNF-dependent inhibition. The mechanism of inhibition shown by BDNF is likely to be similar to a long- term depression (LTD) -like mechanism, because inducing LTD prior to BDNF exposure occluded the BDNF effect, and BDNF exposure prior to LTD induction occluded the LTD effect. The LTD that occluded the BDNF effect was shown to be non-N-methyl-D- aspartic acid receptor (NMDAR) dependent, as it was unaffected by application of an NMDAR antagonist.In chapter 2, we continued to investigate the inhibitory effect of BDNF by exploring the mechanism by which the LFP was reduced. Using a whole-cell patch clamp technique, we found that BDNF reduces the excitatory post synaptic current, EPSC, of both NCB and CB populations without changing the inhibitory post synaptic current, ISPC. BDNF was also found to reduce excitability by significantly increasing rheobase, the amount of current required to elicit a single action potential. Stimulating trains of action potentials resulted in BDNF-exposed cells having a reduction in the amount of action potentials they produced. All together, these findings support BDNF acting to inhibit excitation in these populations of cells. This inhibition by BDNF could be necessary in supporting the synaptic plasticity that is prompted during reorganization.

Prematurity is the leading cause of death in the first month of life. Neonates are forced to engage the extrauterine environment with an underdeveloped nervous systems, with limited connectivity between orofacial sensorimotor anatomy, brainstem pattern-generating circuits, and sensory-driven thalamocortical inputs to layer IV of the neocortex. This is correlated with an inability to produce the complex neuromotor behaviors of oral feeding. The NTrainer System is an assessment and treatment tool that promotes ororhythmic motor patterning in preterm infants though pulsed orocutaneous stimulation to improve NNS. This report represents an interim analysis of NNS development among 42 extremely preterm infants enrolled in an ongoing randomized control trial. Participants, diagnosed with RDS or BPD, were randomized to receive the pulsed orocutaneous or non-pulsed treatment. Digitized records of NNS dynamics were automatically processed using a new Python based software program, NeoNNS, that extracts frequency domain features of NNS performance. Linear mixed modeling was used to examine the effect of treatment type among several dependent variables for 817 NNS files. Significant treatment effects were shown for NNS cycles/min, NNS cycles/burst, max NNS cycles/burst, and NNS amplitude.Infants’ NNS performance increased for some measures when the SHAM was utilized, while the number of bursts per minute and compression cycle amplitude increased the NTrainer therapy. A greater increase in variable measures was observed in RDS infants who received the SHAM. Infants’ diagnosis in combination with treatment as well as sex resulted in no significant effects across all parameters. All measures were highly dependent on PMA. Advisor: Steven M. Barlow

Stroke is the fourth leading cause of death in the United States, and causes tremendous burden due to disability worldwide. Ischemic stroke occurs when blood flow to the brain is blocked, leading to neural cell death if the flow is not re-established. Transcranial Doppler ultrasound (TCD) is a medical imaging modality that measures blood flow in the brain with high temporal resolution. We used TCD to study hemodynamic changes evoked by a pneumotactile somatosensory stimulus applied to the palmar skin of the right hand. The stimulus was generated by a Galileo device and consisted of very short pressures pulses travelling across the hand at traverse velocities ranging from 5 to 65 cm/s. This stimulus shows potential for preventing damage due to ischemic strokes and for rehabilitation of stroke survivors. The goal of this work was to understand how pneumotactile stimulation with the Galileo device affects cerebral blood flow in healthy adults, which will provide a reference for how pneumotactile stimulation with the Galileo will affect cerebral blood flow in adults with chronic and acute stroke. This work first looked at how time length of stimulus affects the maximum percent change in cerebral blood flow velocity (CBFV) and the lateralization of CBFV during pneumotactile somatosensory stimulation using the Galileo device. Three time lengths were used: 10, 20, and 30 s. It was found that the 20 s stimulus length had the largest increase in CBFV and the most lateralized response. We next looked at the hemodynamic output for a particular stimulus velocity and time length to characterize the hemodynamic response function (HRF) for healthy adults. This involved: (1) measuring characteristics of the hemodynamic response function (HRF), (2) comparing percent change over time in the right and left middle cerebral arteries (MCAs) to determine if the response was lateralized, and (3) observing the time course of the transient response to stimulation to see how long it takes for the transient response to return to steady state. It was found that the response did show lateralization, and did return to steady state within 1 minute of stimulus removal. Advisor: Gregory R. Bashford

It has long been suspected that proprioceptive abnormalities underlie the motor problems in children with developmental coordination disorder (DCD). However, current empirical evidence of proprioceptive dysfunction in children with DCD is still inconsistent. To address this issue, this study pursued the following three aims: 1) To obtain objective measures of position sense acuity to verify that children with DCD have proprioceptive deficits. 2) To examine whether the proprioceptive abnormality in children with DCD is joint-specific or a generalized somatosensory deficit that affects distal as well as proximal joints. 3) To investigate the relationship between motor function and position sense acuity in children with and without DCD. Methods: Twenty children with DCD [(Mean age: 10 years 4 months (SD: 3 months); 9 ♂, 11♀) and thirty typically developing (TD) children [M age: 10 years 5 months (SD: 3 months); 14 ♂, 16♀] were recruited and screened using Movement Assessment Battery for Children (MABC-2). The DCD group had total MABC-2 score below 5th percentile, and TD group was above 25th percentile. Using a body-scalable wrist and elbow bimanual manipulandum, proprioceptive status was assessed using 1) a wrist and elbow joint position matching task requiring active movement to reproduce a target position with either the same or the opposite hand/forearm, and 2) a psychophysical two-alternate forced choice test for the wrist that relied on passive motion. It required children to discriminate between two joint positions. We measured both aspects of position sense acuity: bias and precision. Bias indicates the proximity of a sensed limb position corresponds to the true physical position of the limb. Precision represents the random error or the agreement between independent repeated responses and is thus a measure of response consistency. Results: First, in comparison to TD controls children with DCD exhibited a significantly lower position sense precision on both elbow (p < 0.05) and wrist (p < 0.001). Position sense bias during active joint position matching at either joint was not significantly higher in children with DCD. Second, the mean wrist position sense discrimination threshold for passive displacement was highly elevated in DCD group (+171%; p < 0.001). Third, position sense discrimination threshold correlated significantly with upper limb motor (r = -0.40) and balance scores (r= -0.50). Conclusion: This study documents that DCD is associated with a dysfunction of position sense. Furthermore, the proprioceptive dysfunction affected both proximal and distal upper limb joints in children with DCD, which is consistent with a view that proprioceptive dysfunction in DCD is generalized in nature. Given the substantial evidence that proprioceptive deficits degrade motor control, these sensory deficits may partly explain fine motor control impairment in DCD.

The coding of the position of touch on the skin and of the size and shape of the body are both fundamental for interacting with our surrounds. The aim of this thesis was to learn more about the mechanisms of tactile localization and to characterize the principles by which skin-based representations of the body update. It is commonly accepted that skin-based representations of the body are generated from the statistics of touch and other inputs. My studies required skin stimulation customised to account for inter-individual differences in touch sensitivity and forearm shape. Within the constraints of these methodological challenges, the central questions of this thesis were addressed by performing multiple behavioural experiments. In my first study, I tested how touch intensity and history influence touch localization. The study showed that reducing touch intensity increases the variability of pointing responses to touch and results in spatial biases to the middle of the recent history of touch. Thus, I showed that when uncertain about perceived touch location, a strategy is used that minimises localization errors over time. This error minimisation mechanism stabilises our perception of events on the skin and their sensory features. Next, I investigated uncertainty in a motion stimulus by fragmenting it. Studies in vision suggest that missing sensory inputs are filled-in from the surrounds, while previous tactile studies suggest fragmented motion could influence skin-based representations. In my second study, I used a motion stimulus which instantly skipped a spatial gap on the forearm, as if the skin surface had been rearranged. As expected I observed mislocalization toward the spatial gap, consistent with changes to receptive fields of neurons corresponding to the skipped patch. The results of my third study were discordant with expectations about the perceived extent of fragmented motion. However, I identified a novel judgment-dependent perceived shortening of a tactile motion stimulus. My final study found that this judgment contingent effect was accompanied by a perceived shortening of the forearm. Future studies might further explore this linkage between skin-based and higher-order representations of the limbs. The findings from this thesis may be clinically relevant for correcting disordered representations.

Neurons in human somatosensory cortex are somatotopically organized, with sensation from the lower limbs mediated by neurons near the midline of the brain, whereas sensations from the upper body, hands and orofacial surfaces are mediated by neurons located more laterally in a sequential map. Neurons in Brodmann's area (BA) 3b are exquisitely sensitive to tactile stimulation of these skin surfaces. Moreover, the location, velocity and direction of tactile stimuli on the skin's surface are discriminable features of somatosensory processing, however their role in fine motor control and passive detection are poorly understood in health, and as a neurotherapeutic agent in sensorimotor rehabilitation. To better understand the representation and processing of dynamic saltatory tactile arrays in the human somatosensory cortex, high resolution functional magnetic resonance (fMRI) is utilized to delineate neural networks involved in processing these complex somatosensory events to the glabrous surface of the hand. The principal goal of this dissertation is to map the relation between a dynamic saltatory pneumatic stimulus array delivered at 3 different velocities on the glabrous hand and the evoked blood-oxygen level-dependent (BOLD) brain response, hypothesized to involve a network consisting of primary and secondary somatosensory cortices (S1 and S2), insular cortex, posterior parietal cortex (PPC), and cerebellar nuclei. A random-balanced block design with fMRI will be used to record the BOLD response in healthy right-handed adults. Development of precise stimulus velocities, rapid rise-fall transitions, salient amplitude, is expected to optimize the BOLD response. Advisor: Steven M. Barlow

Active sensing, which incorporates closed-loop behavioral selection of information during sensory acquisition, is an important feature of many sensory modalities. We used the rodent whisker tactile system as a platform for studying the role cortical sensory areas play in coordinating active sensing motions. We examined head and whisker motions of freely moving mice performing a tactile search for a randomly located reward, and found that mice select from a diverse range of available active sensing strategies. In particular, mice selectively employed a strategy we term contact maintenance, where whisking is modulated to counteract head motion and sustain repeated contacts, but only when doing so is likely to be useful for obtaining reward. The context dependent selection of sensing strategies, along with the observation of whisker repositioning prior to head motion, suggests the possibility of higher level control, beyond simple reflexive mechanisms. In order to further investigate a possible role for primary somatosensory cortex (SI) in coordinating whisk-by-whisk motion, we delivered closed-loop optogenetic feedback to SI, time locked to whisker motions estimated through facial electromyography. We found that stimulation regularized whisking (increasing overall periodicity), and shifted whisking frequency, changes that emulate behaviors of rodents actively contacting objects. Importantly, we observed changes to whisk timing only for stimulation locked to whisker protractions, possibly encoding that natural contacts are more likely during forward motion of the whiskers. Simultaneous neural recordings from SI show cyclic changes in excitability, specifically that responses to excitatory stimulation locked to whisker retractions appeared suppressed in contrast to stimulation during protractions that resulted in changes to whisk timing. Both effects are evident within single whisks. These findings support a role for sensory cortex in guiding whisk-by-whisk motor outputs, but suggest a coupling that depends on behavioral context, occurring on multiple timescales. Elucidating a role for sensory cortex in motor outputs is important to understanding active sensing, and may further provide novel insights to guide the design of sensory neuroprostheses that exploit active sensing context.

Somatosensory neurons are essential for detecting diverse environmental stimuli, thus critical for survival of mammals. In order to achieve sensory modality specificity, many somatosensory subtypes emerge with various receptor and ion channel expression, as well as terminal morphologies. How the somatosensory system achieves such a high variety of neuronal subtypes is unknown. In this thesis, I used a newly discovered subtype, VGLUT3-expressing unmyelinated low-threshold mechanoreceptors (C-LTMRs), as a model to try to answer this question. C-LTMRs have been proposed to play a role in pleasant touch in humans or pain in mice. Previously, our lab has identified the Runt domain transcriptional factor Runx1 to be pivotal for the development of a cohort of sensory neurons such as pain related nociceptors, thermal receptors, as well as itch related pruriceptors. Here I found that Runx1 is also required to establish all known features associated with C-LTMRs. In search of the mechanism of how Runx1 controls C-LTMR development, I found that the zinc finger protein Zfp521 is predominantly expressed in C-LTMRs and its expression is Runx1 dependent. By generating and analyzing Zfp521 conditional knock out animals, I found Zfp521 is required for part of C-LTMR molecular identities and nerve terminal morphologies. Our studies suggest that Runx1 acts through Zfp521-dependent and Zfp521-independent pathways to specify C-LTMR identities. To study C-LTMR functions, we performed a series of behavioral analysis and found the loss of VGLUT3 and mechanosensitivities in C-LTMRs does not markedly affect acute or chronic mechanical pain measured from the hind paws, which argues against the proposed role of VGLUT3 in C-LTMRs in mediating mechanical pain in mice. In the future, we will continue to use our mutant mice to study physiological functions of C-LTMRs.

The proper function of the nervous system depends on the development andmaintenance of exquisitely precise and often long-reaching neural circuits. This requiresthat immature neurons are accurately guided to their final destination, connected to theircorrect targets, and often restricted at that target to prevent the formation of aberrantconnections. The developmental timecourse and precise topographic arrangement of therodent whisker-barrel somatosensory system has been well documented making it anattractive model for studying the molecular aspects of axonal guidance needed for theaccurate development of these connections. The membrane bound Eph family of receptortyrosine kinase guidance molecules is well suited for the precise control of connectivitynecessary in the somatosensory system. Using RNA and protein detection methods, thetemporal and spatial expression patterns of ephrin-A2, ephrin-A3, EphA4, and EphA7have been described within the vibrissal pad, trigeminal ganglia, ventrobasal thalamus,and primary somatosensory cortex. The possible roles of these guidance molecules in thedevelopment and organization of the somatosensory system are discussed.

Brain-controlled prostheses have the potential to improve the quality of life of a large number of paralyzed persons by allowing them to control prosthetic limbs simply by thought. An essential requirement for natural use of such neural prostheses is that the user should be provided with somatosensory feedback from the artificial limb. This can be achieved by electrically stimulating small populations of neurons in the cortex; a process known as cortical microstimulation. This dissertation describes the development of novel technologies for experimental neuroscience and their use to explore the neural and perceptual effects of cortical microstimulation in rodents. The first part of this dissertation describes the various tools built to study cortical microstimulation in awake, behaving rodents. Circuits were developed to simultaneously record and stimulate neurons in the cortex; thus paving the way for future research into neural responses to stimulation. Further, electrode coatings based on conductive polymers were explored to allow chronic neural stimulation without causing long term damage to the implanted electrodes or neural tissue. Two technologies were then developed to monitor different aspects of rodent behavior. Wireless accelerometers were built to monitor gross behavior and neural network based algorithms were developed to extract behavioral states from such acceleration data. Rats have poor visual acuity and actively scan their facial vibrissae or whiskers to feel the world around them. To study this whisking behavior, a video based whisker tracking system was developed which tracks the movement of a single whisker in real-time.The second part of this dissertation describes advances in neuroscience enabled by these tools. The neural response to microstimulation was explored in awake, behaving rats and it was found that microstimulation in barrel cortex evokes 15-18 Hz oscillations that are strongly modulated by motor behavior. In freely whisking rats, the power of the microstimulation evoked oscillation in the local field potential was inversely correlated to the strength of whisking. This relationship was also present in rats performing a stimulus detection task suggesting that the effect was not due to sleep or drowsiness. Further, a computational model of the thalamocortical loop is presented which recreates the observed phenomenon and predicts some of its underlying causes. These findings demonstrate that stimulus-evoked oscillations are strongly influenced by motor modulation of afferent somatosensory circuits.The perceptual effects of cortical microstimulation were then explored using behavioral studies. Tactile exploration of the environment involves the active movement of external mechanoreceptors and the integration of information across sensory and motor modalities. To explore the encoding of somatosensory feedback in such an active sensing system, a novel behavioral paradigm was introduced which precisely controls cortical microstimulation in real-time based on the movements of the animal. Using a real-time whisker tracking system, microstimulation was delivered in barrel cortex of actively whisking rats when their whisker crossed a software-defined target. Rats learned to rapidly integrate microstimulation cues with their knowledge of whisker position to compute target location along the rostro-caudal axis. This showed that rats can perform sensorimotor integration using electrically delivered stimuli. Moreover, it was discovered that rats trained to respond to cortical microstimulation responded similarly to physical whisker deflection suggesting that microstimulation in barrel cortex induces tactile percepts. This ability to encode tactile percepts in active sensing systems may be critical for providing the sense of touch to future users of motor neuroprostheses.

The primary goal of this dissertation was to examine the long-term effect of prenatal alcohol exposure (PAE) on the primary somatosensory (SI) and primary motor cortex (MI). For over 30 years, PAE has been shown to produce a triad of symptoms (growth deficits, craniofacial dysmorphologies and central nervous system disruptions) diagnosed as fetal alcohol syndrome (FAS) in children and adults. Since low to moderate levels of prenatal alcohol exposure are less likely to produce FAS symptoms in children, the term “PAE” in this dissertation typically refers to heavy/abusive/chronic levels of prenatal alcohol exposure (in humans this equates to 5+ drinks/per occasion/1+ times per week) administered in a chronic binge-type fashion having a high potential to cause FAS. However, it must be pointed out that the most important factor in studies dealing with PAE in humans or animals is the peak blood alcohol level (BAL) and next are the temporal and spatial parameters dealing with high BALs. It is evident that children with FAS frequently show major deficits in information processing, which is one of the major functions of the sensorimotor system. Two major components of the sensorimotor system are the cortical input to layer IV primary sensory cortex (SI) and output from layers V and VI primary motor cortex (MI). Therefore, the focus of this dissertation is on PAE-related anatomical and physiological deficits in SI and MI that are likely to play a role in the multiple sensorimotor, behavioral, and learning disruptions seen in children with FAS. The similarities in rodent and human cortical organization make rodents excellent models for elucidating the influence of PAE on the sensorimotor system. Of particular note is the highly organized human and rodent sensorimotor system with the sensory input and motor output arranged into structural and functional columns. However, one difference between humans and rodents is that the latter receives its sensory information in layer IV cortex into cell aggregates termed “barrels,” whereas humans have no such specific cortical structures per se. Each barrel in rodent cortex is spatially related to sensory receptors that innervate specific regions of the body surface, thus barrels produce a cortical somatic map. The longest studied and most easily identifiable barrel region is the posterior medial barrel subfield (PMBSF), representing mystacial vibrissae of the rodent. A second highly studied region of the barrel cortex is the forepaw barrel subfield (FBS), representing the forepaw. One hallmark feature of PAE is the behavioral disruptions seen in fine motor control. These deficits may be due to disruptions in both SI and MI. Like SI, MI is also well organized into specific cortical regions associated with eliciting motor responses. Because SI and MI are highly organized, these cortical regions are very useful for studying the effect of prolonged PAE-related sensorimotor disruptions. The primary goal of this dissertation was to examine the long-term consequences of PAE on SI and MI in 6-week-old (juvenile) or 7-month-old (adult) rats. To accomplish this goal, four major experiments were carried out utilizing a binge-type alcohol exposure paradigm on pregnant rat dams followed by an examination of the PAE pups as well as untreated control and nutritional control pups at six weeks and seven months of age. Experiment 1: We tested the hypothesis (Chapter 2) that PAE would reduce the PMBSF area in juvenile and adult rats. Results indicated that PAE significantly reduced the PMBSF area, the total PMBSF barrel area, and interbarrel septa area in PAE juveniles and adult rats. Furthermore, PAE effects were asymmetrical across the PMBSF, as the areas of posterior barrels were less reduced than anterior barrel areas. By combining barrels into lateral-to-medial running “arcs” and calculating the area as a percent difference from respective chowfed (CF) or pairfed (PF) arcs, results suggested a split in the PMBSF between a more reduced anterior region and a less reduced posterior region. The areas of anterior arcs of PMBSF were always more reduced than the areas of posterior arcs. However, a similar asymmetric pattern was not identified in anterior to posterior running rows. Experiment 2: The goal of Experiment 2 (Chapter 2) was to test the hypothesis that the rostrocaudal asymmetry identified in Experiment 1 was due, in part, to differential sensory experience across the mystacial pad. It is well established that numerous peripheral and CNS asymmetries already occur by way of variations in mystacial pad vibrissae lengths, base widths, vibrissae behavior, peripheral innervation patterns, and metabolic activity levels within cortical PMBSF barrels. It was hypothesized that trimming the mystacial pad would eliminate any differences between posterior and anterior vibrissae, in turn affecting the vibrissae cortical barrel representations and subsequent PMBSF asymmetries. To test this hypothesis, unilateral mystacial vibrissae were trimmed in EtOH and CF rats from postnatal day five (PD5) to PD42. EtOH rats sacrificed on PD42 had their individual PMBSF area and individual PMBSF barrel areas measured. These areas were then compared to respective PMBSF and barrel areas of the ipsilateral cortex from a CF group that had also undergone vibrissae trimming, and the percent change was calculated. Results indicated that vibrissae trimming did not affect the asymmetry identified in Chapter 2. Experiment 3: We tested the hypothesis that PAE would significantly reduce the area of the FBS morphology and the area of the peripheral glabrous forepaw (Chapter 3). The FBS morphology and peripheral glabrous forepaw areas were significantly reduced in juvenile rats following PAE. Experiment 4: This experiment was carried out to test the hypothesis that PAE would reduce the physiological/functional forepaw representation and also delay evoked response latency between periphery and SI (Chapter 4). Using carbon-fiber electrodes inserted into layer IV cortex, the physiological forepaw representation was mapped by lightly tapping the forepaw periphery (i.e., digits, or pads) with a dull insect pin and recording forepaw receptive fields in the cortex. PAE significantly reduced the representation of the entire glabrous forepaw surface as well as the physiological forepaw representation. Experiment 5: We tested the hypothesis that PAE would reduce the size of the primary motor cortex (MI), specifically those regions responsible for contralateral vibrissae and forepaw movement (Chapter 5). Results indicated that PAE significantly reduced MI areas for mystacial vibrissae and forepaw motor cortex. Results from Experiments 1 to 5 reinforce the hypothesis that PAE has a long-term effect on the sensorimotor system and provides new information on the effect of PAE on MI. The sensorimotor system is important for processing peripheral information and performing planned motor movements. Therefore, deficits in this system may be among the underlying mechanisms for reported clinical symptoms, such as the disturbances in balance, posture, fine motor control, attention, learning, reaction time, and other information disruptions often identified in children exposed to high levels of alcohol in utero.

Previous studies from our laboratory have demonstrated that, in adult rats following forelimb amputation on the day of birth, approximately one-third of multi-unit recording sites in the forelimb-stump representation of primary somatosensory cortex (SI)also respond to cutaneous stimulation of the hindlimb (on the amputated side) when cortical GABAA+B receptors are pharmacologically blocked (GRB). These normally suppressed hindlimb inputs originate in the SI hindlimb representation and synapse in the dysgranular cortex before reaching the SI forelimb-stump representation. The experiments in this thesis tested three hypotheses based on these findings. The first hypothesis is that the development of SI contributes to the deferential “invasion” of the deafferented SI forelimb-stump region by hindlimb rather than face inputs. This was tested by comparing SI maps in fetal, neonatal, and adult amputees. There was significant expression of face receptive fields in fetal amputees during GRB, compared to hindlimb responses in neonatal amputees, and none in adult amputees. These findings demonstrate that the developmental state of SI at the time of amputation does influence whether face or hindlimb inputs are expressed in the deafferented zone during GRB. The second hypothesis is that the suppression of hindlimb responses in neonatal amputees is locally mediated by GABAergic synapses within the SI forelimb-stump zone. This was tested by making separate targeted GRB injections at individual recording sites, in the SI hindlimb region, and in the dysgranular cortex, followed by continuous monitoring for the presence of hindlimb responses. Hindlimb responses were revealed primarily by the local recording site 211 injections, indicating that the GABAergic suppression of hindlimb responses is indeed locally mediated. This is consistent with the morphology of inhibitory SI nterneurons. The third hypothesis is that hindlimb responses can be revealed by downregulating one known source of SI input, the contralateral SI representation. This was tested by inactivating the contralateral SI forelimb region via lidocaine injections, and monitoring SI forelimb-stump sites for hindlimb responses. This manipulation did reveal hindlimb responses, although not to the same extent as that found in the same animals during GRB. This demonstrates that hindlimb responses can be revealed independent of GRB, by reducing one source of excitatory drive to SI GABAergic neurons.

Adequate postural control depends on the spatial and temporal integration of vestibular, visual, and somatosensory information about the active and passive motion of the head and body. Individuals who are unable to quickly select the most reliable source of sensory information from those available are at risk for falling whenever the sensory environment changes suddenly. Changes in maintenance of stance are multifactorial, involving the processing of multiple sensory inputs and the selection and weighting of these inputs for an appropriate postural response. We hypothesized that reorganization of postural control relying on these multiple inputs, due to exposure to microgravity, healthy aging, or balance system pathology, would result in not only greater amounts of sway, but also changes in interjoint coordination. We tested this hypothesis by examining the multivariate characteristics of postural sway and comparing the postural control gains used for maintenance of upright stance during the altered sensory conditions of the Sensory Organization Test (EquiTest, NeuroCom International). We improved the sensitivity of the Sensory Organization Test with the use of direct kinematic measurements for assessment of postural sway as well as to provide a more direct feedback signal for sway-referencing of the balance platform or visual surround. We used the covariance of hip and ankle kinematics as a measure of joint motion and interjoint coordination, and then utilized discriminant analysis to further examine these sway characteristics. Our results suggest that after spaceflight, astronauts exhibit significant multivariate changes in multijoint coordination, of which increased sway is only one component. Similarly, our results suggest that the contributions of visual vestibular and somatosensory information for postural control are altered with healthy aging. These coordinative changes are partially explained by diminished sensory perception of spatial orientation, as well as a change in the feedback response to altered sensory inputs. Such changes are consistent with reweighting of vestibular inputs and changes in control strategy in a multivariable control system. Additionally, the use of hip and shank kinematics with shank angle sway-referencing can provide new clinical information regarding the postural control of balance disorder patients as well as further classification of functional compensation.