Thesis (Ph.D.)--Brown University, 2005. / Vita. Thesis advisor: John P. Donoghue. Includes bibliographical references (leaves 40-48, 78-80, 148-151, 229-231, 267-268). Also available online.

Thesis (Ph. D.)--University of Washington, 2007. / Vita. Includes bibliographical references (leaves 158-196).

No description available.

The primary motor cortex (M1) is an important site for learning new motor skills. While rewardis known to both enhance and accelerate motor learning, the mechanism by which reward exertsthese effects remains unclear. Previous studies in primates have demonstrated reward-relatedactivity in M1, however, it is not known whether reward is represented among different neuronalcell types in M1, or if the representations change over the course of reward-based associativelearning. We begin by reviewing advances in optogenetic methods that have enabled thedissection of cortical circuits underlying sensorimotor behaviours with a special focus on thefunctional roles of cell-type specific connections in governing sensorimotor informationprocessing and learning and memory. We then used in vivo, two-photon calcium imaging tocharacterize reward and reward-related responses in pyramidal neurons (PNs), PV-INs, SST-INsand VIP-INs while mice simultaneously performed a head-fixed auditory classical conditioningtask. We found that different cell types had distinct responses to the conditioned stimulus (CS)and to reward, and these responses underwent differential changes over the course of associativelearning. Notably, VIP-INs preferentially represented reward and their reward responsesincreased with learning, while PV-INs preferentially represented the CS, and their CS responsesincreased with learning. Lastly, to identify which brain regions might provide reward-relatedinput to VIP-INs, we performed cell-type specific monosynaptic rabies tracing and generatedcomparative brain-wide maps of input to VIP-INs, PV-INs, SST-INs and PNs in M1. Weidentified preferential input from the orbital frontal cortex (ORB) to VIP-INs compared to theother IN subtypes. These results suggest that ORB may convey reward-related input to VIP-INsand thereby disinhibit local MOP circuitry during reward-based learning. Together, these studiesprovide a potential mechanism for how reward modulates motor learning.

Post-concussion syndrome (PCS) is a poorly understood sequela of mild traumatic brain injury (mTBI), more commonly referred to as concussion. While PCS is known to affect a subset of individuals following injury, it remains unclear how and why specific individuals incur chronic symptoms. Concussions disrupt normal neurophysiologic function within the brain, however the neurophysiologic underpinnings of PCS are unclear. Using transcranial magnetic stimulation (TMS), it is possible to non-invasively investigate neurotransmission in clinical populations such as those with PCS by stimulating the primary motor cortex (M1) and recording motor outputs in a contralateral hand muscle. A study was conducted using TMS to measure corticospinal excitability, intracortical facilitation and inhibition, and transcallosal inhibition in M1 of a group with PCS and a non-injured, healthy control group. Greater corticospinal excitability, and specific reductions in intracortical and transcallosal inhibition were observed in the PCS group, providing evidence of impaired neurotransmitter receptor activity. Importantly, these findings differed from previous observations in recovered concussion groups using similar stimulation techniques. Furthermore, it was observed that these neurophysiological differences may relate specifically to the presence of depression symptoms rather than general concussion symptoms. The physiologic and clinical implications of the findings of this thesis are discussed, and novel research avenues warranting investigation are identified. / Thesis / Master of Science in Kinesiology

The activity of cortical neurons in awake brains changes dynamically as a function of the behavioural and attentional state. The primary motor cortex (M1) plays a central role in regulating complex motor behaviors. Despite a growing knowledge on its connectivity and spiking pattern, little is known about intra-cellular mechanism and rhythms underlying motor-command generation. In the last decade, whole-cell recordings in awake animals has become a powerful tool for characterising both sub-and supra-threshold activity during behaviour. Seminal in vivo studies have shown that changes in input structure and sub-threshold regime determine spike output during behaviour (input-output transformations). In this thesis I make use of computational and experimental techniques to better understand (i) how the brain regulates the sub-threshold activity of the neurons during movement and (ii) how this reflects in their input-output transformation properties. In the first part of this work I present a novel probabilistic technique to infer input statistics from in-vivo voltage-clamp traces. This approach, based on Bayesian belief networks, outperforms current methods and allows an estimation of synaptic input (i) kinetic properties, (ii) frequency, and (iii) weight distribution. I first validate the model on simulated data, thus I apply it to voltage-clamp recordings of cerebellar interneurons in awake mice. I found that synaptic weight distributions have long tails, which on average do not change during movement. Interestingly, the increase in synaptic current observed during movement is a consequence of the increase in input frequency only. In the second part, I study how the brain regulates the activity of pyramidal neurons in the M1 of awake mice during movement. I performed whole-cell recordings of pyramidal neurons in layer 5B (L5B), which represent one of the main descending output channels from motor cortex. I found that slow large-amplitude membrane potential fluctuations, typical of quiet periods, were suppressed in all L5B pyramidal neurons during movement, which by itself reduced membrane potential (Vm) variability, input sensitivity and output firing rates. However, a sub-population of L5B neurons ( 50%) concurrently experienced an increase in excitatory drive that depolarized mean Vm, enhanced input sensitivity and elevated firing rates. Thus, movement-related bidirectional modulation in L5B neurons is mediated by two opposing mechanisms: 1) a global reduction in network driven Vm variability and 2) a coincident, targeted increase in excitatory drive to a subpopulation of L5B neurons.

The primary motor cortex (M1) is a key brain area for the generation and control of motor behaviour. Output from M1 can be driven in part by long-range inputs from a collection of thalamic nuclei termed the motor thalamus (MTh), but how MTh input shapes activity in M1 and forelimb motor behaviour remains largely unresolved. To address this issue, we first defined the 3D anatomical coordinates of mouse forelimb motor thalamus (MThFL) by employing conventional retrograde and virus-based tracing methods targeted to the forelimb region of M1 (M1FL). These complimentary approaches defined MThFL as a ~0.8 mm wide cluster of neurons with anatomical coordinates 1.1 mm caudal, 0.9 mm lateral to bregma and 3.2 mm below the pial surface. Thus, MThFL incorporates defined areas of the ventrolateral, ventral anterior and anteromedial thalamic nuclei. To investigate the importance of M1FL and MThFL during skilled motor behaviour, we developed and optimised a quantitative behavioural paradigm in which head-restrained mice execute forelimb lever pushes in response to an auditory cue to receive a water reward. Forelimb movement trajectories were mapped using high-speed digital imaging and multi-point kinematic analysis. We inactivated both M1FL and MThFL of mice performing this motor behaviour using a pharmacological strategy, which in both cases resulted in a significant reduction in task performance. Inactivating M1FL significantly affected forelimb coordination and dexterity, resulting in erratic motion and posture. In contrast, mice with MThFL inactivated displayed a reduction in total motor output, although correct posture was maintained. We performed extracellular recordings in MThFL of expert-level mice, demonstrating that motor thalamic output during execution of task was dominated by a robust response to the onset of the auditory cue. Cue-evoked responses were also observed in motor thalamic neurons of naive mice. We have developed a novel solution to the stability problem encountered when performing whole-cell patch-clamp recordings from the motor cortex of head-restrained mice performing forelimb motor behaviour, and present preliminary recordings maintained through the execution of forelimb behaviour.

The neural correlates of bilateral upper limb movement are poorly understood. It has been proposed that interhemispheric pathways contribute to the modulation of motor cortical excitability during bimanual movements, possibly via direct connections between primary motor areas (M1), or via a central cortical structure, such as the supplementary motor area (SMA). The ability of one hemisphere to facilitate activation in the other presents a unique opportunity for motor rehabilitation programs using bilateral movements. The focus of this thesis was to investigate the mechanisms underlying bimanual movements in a group of healthy control participants using functional magnetic resonance imaging (fMRI), and subsequently to identify the types of movements that are most likely to maximize M1 activity. It was hypothesized first, that movements involving more proximal muscles, which are known to have a greater number of transcallosal connections, would produce a larger facilitation of M1 activity; and secondly, that the greatest facilitation would occur during those phases of movements where homologous muscles are active simultaneously (i.e. in-phase bilateral movements). The current results demonstrate that the M1 regions and the SMA work together to modulate motor cortical excitability, and that the greatest modulation of activity is seen during movements involving proximal muscles. The findings presented may have clinical relevance to motor rehabilitation programs involving bilateral movements.

The neural correlates of bilateral upper limb movement are poorly understood. It has been proposed that interhemispheric pathways contribute to the modulation of motor cortical excitability during bimanual movements, possibly via direct connections between primary motor areas (M1), or via a central cortical structure, such as the supplementary motor area (SMA). The ability of one hemisphere to facilitate activation in the other presents a unique opportunity for motor rehabilitation programs using bilateral movements. The focus of this thesis was to investigate the mechanisms underlying bimanual movements in a group of healthy control participants using functional magnetic resonance imaging (fMRI), and subsequently to identify the types of movements that are most likely to maximize M1 activity. It was hypothesized first, that movements involving more proximal muscles, which are known to have a greater number of transcallosal connections, would produce a larger facilitation of M1 activity; and secondly, that the greatest facilitation would occur during those phases of movements where homologous muscles are active simultaneously (i.e. in-phase bilateral movements). The current results demonstrate that the M1 regions and the SMA work together to modulate motor cortical excitability, and that the greatest modulation of activity is seen during movements involving proximal muscles. The findings presented may have clinical relevance to motor rehabilitation programs involving bilateral movements.

In adult rats, following unilateral stroke-like injury to the motor cortex, there is significant loss of function in the forelimb contralateral to the ischemic damage. In the remaining motor cortex, changes in neuronal activation patterns and connectivity are induced following motor learning and rehabilitation in the brains of adult animals. Rehabilitative training promotes functional recovery of the impaired forelimb following motor cortical strokes; however, its benefits are most efficacious when coupled with other rehabilitative treatments. Multiple lines of evidence suggest that focal cortical electrical stimulation (CS) enhances the effectiveness of rehabilitative training (RT) and promotes changes in neural activation and plasticity in the peri-lesion motor cortex. Specific examples of plastic events include increases in dendritic and synaptic density in the peri-lesion cortex following CS/RT compared to rehabilitative training alone. The objective of these studies was to investigate which conditions, such as timing and method of delivery of CS, when coupled with RT, are most efficacious in promoting neuronal plasticity and functional recovery of the impaired forelimb following ischemic cortical injury in adult animals. The central hypothesis of these dissertation studies is that, following unilateral stroke-like injury, CS improves the functional recovery of the impaired forelimb and promotes neural plasticity in remaining motor cortex when combined with RT. This hypothesis was tested in a series of experiments manipulating post-ischemic behavioral experience with the impaired forelimb. Adult rats were proficient in a motor skill (Single Pellet Retrieval Task) and received ischemic motor cortex lesion that caused impairments in the forelimb. Rats received daily rehabilitative training on a tray reaching task with or without concurrent cortical stimulation. Epidural cortical stimulation, when paired with rehabilitative training, resulted in enhanced reaching performance compared to RT alone when initiated 14 days after lesion. These results were found to be maintained well after the treatment period ended. Rats tested 9-10 months post-rehabilitative training on the single pellet retrieval task continued to have greater reaching performance compared to RT alone. However, delayed onset of rehabilitative training (3 months post-infarct) indicated that CS does not further improve forelimb function compared to RT along. It was further established that CS delivered over the intact skull (transcranial stimulation) of the lesioned motor cortex was not a beneficial adjunct to rehabilitative training. Together these dissertation studies provide insight into the effectiveness and limitations of CS on behavioral recovery. The findings in these studies are likely to be important for understanding how post-stroke behavioral interventions and adjunct therapies could be used to optimize brain reorganization and functional outcome. / text