abstract: Navigation through natural environments requires continuous sensory guidance. In addition to coordinated muscle contractions of the limbs that are controlled by spinal cord, equilibrium, body weight bearing and transfer, and avoidance of obstacles all have to happen while locomotion is in progress and these are controlled by the supraspinal centers. For successful locomotion, animals require visual and somatosensory information. Even though a number of supraspinal centers receive both in varying degrees, processing this information at different levels of the central nervous system, especially their contribution to visuo-motor and sensory-motor integration during locomotion is poorly understood. This dissertation investigates the patterns of neuronal activity in three areas of the forebrain in the cat performing different locomotor tasks to elucidate involvement of these areas in processing of visual and somatosensory information related to locomotion. In three studies, animals performed two contrasting locomotor tasks in each and the neuronal activities were analyzed. In the first study, cats walked in either complete darkness or in an illuminated room while the neuronal activity of the motor cortex was recorded. This study revealed that the neuronal discharge patterns in the motor cortex were significantly different between the two illumination conditions. The mean discharge rates, modulation, and other variables were significantly different in 49% of the neurons. This suggests a contextual correlation between the motor cortical activity and being able to see. In two other studies, the activities of neurons of either the somatosensory cortex (SI) or ventrolateral thalamus (VL) were recorded while cats walked on a flat surface (simple locomotion) or along a horizontal ladder where continuous visual and somatosensory feedback was required (complex locomotion). We found that the activity of all but one SI cells with receptive fields on the sole peaked before the foot touched the ground: predictably. Other cells showed various patterns of modulation, which differed between simple and complex locomotion. We discuss the predictive and reflective functionality of the SI in cyclical sensory-motor events such as locomotion. We found that neuronal discharges in the VL were modulated to the stride cycle resembling patterns observed in the cortex that receives direct inputs from the VL. The modulation was stronger during walking on the ladder revealing VL’s contribution to locomotion-related activity of the cortex during precision stepping. / Dissertation/Thesis / Doctoral Dissertation Neuroscience 2016

abstract: The activation of the primary motor cortex (M1) is common in speech perception tasks that involve difficult listening conditions. Although the challenge of recognizing and discriminating non-native speech sounds appears to be an instantiation of listening under difficult circumstances, it is still unknown if M1 recruitment is facilitatory of second language speech perception. The purpose of this study was to investigate the role of M1 associated with speech motor centers in processing acoustic inputs in the native (L1) and second language (L2), using repetitive Transcranial Magnetic Stimulation (rTMS) to selectively alter neural activity in M1. Thirty-six healthy English/Spanish bilingual subjects participated in the experiment. The performance on a listening word-to-picture matching task was measured before and after real- and sham-rTMS to the orbicularis oris (lip muscle) associated M1. Vowel Space Area (VSA) obtained from recordings of participants reading a passage in L2 before and after real-rTMS, was calculated to determine its utility as an rTMS aftereffect measure. There was high variability in the aftereffect of the rTMS protocol to the lip muscle among the participants. Approximately 50% of participants showed an inhibitory effect of rTMS, evidenced by smaller motor evoked potentials (MEPs) area, whereas the other 50% had a facilitatory effect, with larger MEPs. This suggests that rTMS has a complex influence on M1 excitability, and relying on grand-average results can obscure important individual differences in rTMS physiological and functional outcomes. Evidence of motor support to word recognition in the L2 was found. Participants showing an inhibitory aftereffect of rTMS on M1 produced slower and less accurate responses in the L2 task, whereas those showing a facilitatory aftereffect of rTMS on M1 produced more accurate responses in L2. In contrast, no effect of rTMS was found on the L1, where accuracy and speed were very similar after sham- and real-rTMS. The L2 VSA measure was indicative of the aftereffect of rTMS to M1 associated with speech production, supporting its utility as an rTMS aftereffect measure. This result revealed an interesting and novel relation between cerebral motor cortex activation and speech measures. / Dissertation/Thesis / Doctoral Dissertation Speech and Hearing Science 2018

A estimulação do córtex motor (CM) é usada para tratar pacientes com síndromes dolorosas resistentes a outros tratamentos. Dados do nosso grupo demonstram que a estimulação do córtex motor (ECM) induz analgesia em ratos, e este efeito depende de opióides. Este estudo investigou a topografia do efeito antinociceptivo induzido pela ECM e o padrão de ativação neuronal na coluna posterior da medula espinal (CPME) e na PAG pela expressão de Fos e Egr-1. Ratos receberam implantes de eletrodos transdurais posicionados sobre áreas distintas do CM equivalentes à: patas anterior, posterior, vibrissas e cauda e após 1 semana passaram por sessões de ECM de 15min, sendo então avaliados nos testes comportamentais: pressão da pata, monofilamentos de von Frey, von Frey eletrônico e pinçamento da cauda. A ECM induziu analgesia no membro equivalente à área do CM estimulada em cada grupo, envolvendo a inibição da CPME, demonstrada pela diminuição da imunoreatividade nas lâminas superiores; e ativação do sistema de analgesia endógeno, pelo aumento da imunoreastividade na PAG. / Stimulation of the motor cortex (MC) has been used to treat patients with pain syndromes resistant to other treatments. Data from our group demonstrates that electrical stimulation of the motor cortex (MCS) induces opioid-dependent analgesia in rats. This study investigated the topography of the antinociceptive effect induced by MCS and the pattern of neuronal activation in the dorsal horn of the spinal cord (DHSC) and in the PAG through Fos and Egr-1 expression. Rats received implantation of transdural electrodes positioned on distinct areas of the corresponding MC: fore limb, hind limb, whiskers and tail and after 1 week were submitted to 15min. MCS sessions, and were evaluated in behavioral tests: paw pressure test, von Frey microfilaments, electronic von Frey and tail pinch. MCS induced analgesia only in the limb area corresponding to the stimulated MC in each group, involving the inhibition of DHSC, demonstrated by decrease of immunoreactivity in the superficial laminae; and activation of endogenous analgesia systems, by the increase of PAG immunoreactivity.

The locus coeruleus (LC) projects ubiquitously to the cortex, and noradrenaline (NA) exerts powerful neuromodulatory control on cortical excitation and inhibition. Previous work has shown that NA plays an important role in motor processes, and further posits that dysregulation in NA function could be one of the culprits of motor-related deficits in many neurodevelopmental disorders, including Autism Spectrum Disorder. In order to characterize the change in NA levels during motor learning in awake and behaving mice, I employed a newly developed optical NA sensor, combined with in vivo two-photon imaging, to visualize spatiotemporal activation patterns of NA in the motor cortex. This experimental approach allows us to track and chronically image the same region of the motor cortex over multiple days, thus permitting the characterization of NA activity throughout the entirety of the motor learning process. I found that NA levels increase significantly during the initial phase of learning, which coincides with the structural and functional plastic changes that have been previously reported in the motor cortex during early stages of motor learning. The NA activity returns to baseline levels as the mice develop their movement strategy; however, the regions of NA release become more spatially clustered during the learning process. The results reported in this thesis provide a novel glimpse into the dynamics of NA activity in the motor cortex during motor learning, and it will provide new direction for the development of therapeutic strategies and diagnostic criteria for motor-related dysfunction in neurodevelopmental diseases.

L’aphasie est un symptôme fréquent après un AVC et a un impact majeur social, économique, médical et psychologique sur les patients. Des études récentes ont tenté avec peu de succès de rechercher des critères pronostiques cliniques précoces de récupération d’une aphasie. L’enjeu de cette possibilité de prédiction est un enjeu majeur clinique et scientifique et peut influencer la prise en charge ré-éducative décidée dès les premiers jours après l’AVC. De plus, l’étude clinico-physiologique de la récupération du langage permettrait de mieux comprendre les mécanismes de plasticité cérébrale mis en jeux. Tout d’abord, nous allons nous intéresser chez le sujet sain à l’implication du cortex moteur dans des tâches de perception, renforçant l’idée que cette structure anatomique jouerait un rôle plus étendu que celui auquel elle a été reléguée pendant de nombreuses années, puis nous allons explorer des facteurs prédictifs de la récupération de l’aphasie, les facteurs langagiers dans un premier temps et des facteurs électrophysiologiques, notamment via la TMS explorant l’intégrité du cortex moteur, et leur contribution dans la prédiction de la récupération. / Considering the high incidence of post-stroke aphasia and its significant social and economic impact, better understanding the mechanisms of language recovery in order to predict patient’s outcome and to optimize rehabilitation is a clinical and scientific challenge. Here we aimed to study whether the motor cortex is involved in speech and language perception, suggesting this structure could play a crucial role. Then, we investigated whether some language features could contribute to the prognosis of aphasia recovery. Finally, we investigated whether the anatomofunctional evaluation of the corticomotor pathway using TMS could improve the prediction of post stroke aphasia recovery.

京都大学 / 0048 / 新制・課程博士 / 博士(医学) / 甲第20075号 / 医博第4168号 / 新制||医||1018(附属図書館) / 33191 / 京都大学大学院医学研究科医学専攻 / (主査)教授 渡邉 大, 教授 林 康紀, 教授 瀬原 淳子 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DGAM

Myeloarchitecture is a prominent feature that can identify the primary motor and sensory areas in the cerebral cortex and is increasingly imaged in magnetic resonance imaging (MRI) studies of cortical parcellation in humans. However, MRI studies of cortical myeloarchitecture are technically difficult for two reasons: the cortex is only a few millimeters thick, and intracortical contrast due to myelin is much smaller than the overall anatomical contrast between cortical tissue and underlying white matter that is typically utilized in imaging. The research in this thesis thus presents specific MRI protocols to visualize intracortical myelin, image processing protocols to delineate the heavily myelinated cortex from the adjacent typical cortex and the application of these techniques in the precentral motor cortex to study morphology of the highly myelinated dorso-medial part, consisting of Brodmann area (BA) 4 and part of BA 6. Optimization of the MRI protocols involved determining the sequence parameters for a T1-weighted MRI sequence to obtain maximal intracortical contrast at 0.7 mm isotropic resolution in imaging time of 15 min, based on T1 differences between cortex that is myelinated (GMm) or unmyelinated (GM). As part of the optimization, T1 values were measured in the following brain tissues: GM, GMm and white matter (WM). The optimization was carried out by simulating the MRI signal for a 3D, magnetization prepared, gradient echo sequence, using the measured T1 values in the analytical signal equations. It was found that lengthening the time delay at the end of each inner phase encoding loop increased the intracortical contrast. The optimization of MRI protocols also included implementing techniques to reduce radio frequency field (B1) inhomogeneities. It was found that dividing the optimized, T1-weighted MRI with a predominantly proton density weighted image resulted in a ratio image with significantly reduced B1 inhomogeneities. The goal of the image processing protocols developed in this thesis was to visualize the variation of intracortical myelin across the precentral motor cortex and to delineate its well-myelinated dorso-medial part. The myeloarchitectonic feature that was selected to visualize the variation in intracortical myelination was the thickness of GMm in the deeper parts of the cortex relative to the cortical thickness, referred to as the proportional myelinated thickness (p). To measure p, the following processing steps were performed. The ratio image was segmented into four tissues: GM, GMm, WM and cerebrospinal fluid (CSF) using fuzzy C-means clustering technique. Using a level set approach, thickness of the cortex was determined as the distance between the outer boundaries of GM and WM and thickness of GMm or myelinated thickness (m) was determined as the distance between the outer boundaries of GMm and WM. The proportional myelinated thickness p, was calculated as follows: p= m/t. The well-myelinated dorso-medial part of the precentral cortex, referred to as Mm, was distinguishable from the adjacent cortex when the proportional myelinated thickness was projected on the outer cortical surface. The optimized MRI and image processing techniques developed in this thesis were used to investigate cortical plasticity in amputees. Two morphological features of the myeloarchitecture over Mm, the mean proportional myelinated thickness and area, were measured in four lower limb amputees and four matched controls. A comparison of these morphological features showed no statistically significant difference (p < 0.05) between the two groups. / Thesis / Doctor of Philosophy (PhD)

As theoretical neuroscience has grown as a field, machine learning techniques have played an increasingly important role in the development and evaluation of theories of neural computation. Today, machine learning is used in a variety of neuroscientific contexts from statistical inference to neural network training to normative modeling. This dissertation introduces machine learning techniques for use across the various domains of theoretical neuroscience, and the application of these techniques to build theories of neural circuits. First, we introduce a variety of optimization techniques for normative modeling of neural activity, which were used to evaluate theories of primary motor cortex (M1) and supplementary motor area (SMA). Specifically, neural responses during a cycling task performed by monkeys displayed distinctive dynamical geometries, which motivated hypotheses of how these geometries conferred computational properties necessary for the robust production of cyclic movements. By using normative optimization techniques to predict neural responses encoding muscle activity while ascribing to an “untangled” geometry, we found that minimal tangling was an accurate model of M1. Analyses with trajectory constrained RNNs showed that such an organization of M1 neural activity confers noise robustness, and that minimally “divergent” trajectories in SMA enable the tracking of contextual factors. In the remainder of the dissertation, we focus on the introduction and application of deep generative modeling techniques for theoretical neuroscience. Specifically, both techniques employ recent advancements in approaches to deep generative modeling -- normalizing flows -- to capture complex parametric structure in neural models. The first technique, which is designed for statistical generative models, enables look-up inference in intractable exponential family models. The efficiency of this technique is demonstrated by inferring neural firing rates in a log-gaussian poisson model of spiking responses to drift gratings in primary visual cortex. The second technique is designed for statistical inference in mechanistic models, where the inferred parameter distribution is constrained to produce emergent properties of computation. Once fit, the deep generative model confers analytic tools for quantifying the parametric structure giving rise to emergent properties. This technique was used for novel scientific insight into the nature of neuron-type variability in primary visual cortex and of distinct connectivity regimes of rapid task switching in superior colliculus.

Indiana University-Purdue University Indianapolis (IUPUI) / Sphingosine-1-phosphate (S1P) is a bioactive sphingolipid that mediates a wide spectrum of biological processes including apoptosis, immune response and inflammation. S1P receptor (S1PR) ligands have been utilized as an effective immunosuppressant, treatment in multiple sclerosis and studied as a treatment for pain. The primary cellular response to S1P is thought to be elicited through S1PR type 1 (S1PR1). My first goal was to understand how S1PR1 signaling affects neuronal excitability in the central amygdala (CeA), a supraspinal node of the descending pain pathway. The CeA is made up of a heterogenous population of neurons which form complex local and long-range circuits. The central lateral amygdala (CeL) consists of two major populations of inhibitory neurons identified by expression of the peptides somatostatin (Sst) and protein kinase Cδ (PKCδ). Sst neurons have been shown to maintain control over local circuits within the CeL and play a critical role in pain modulation. I utilized transgenic breeding strategies to fluorescently label Sst-expressing CeL neurons for whole-cell electrophysiology in acute brain slice. This strategy allowed me to study the effects of S1PR1 agonist SEW2871 and S1PR1 antagonist NIBR on the cellular physiology of CeL Sst neurons. My findings reveal intrinsically distinct subtypes of CeL Sst neurons that are uniquely affected by S1PR1 activation, which may have implications for how S1P alters supraspinal pain pathways. My second goal was to assess the physiology of motor cortex neurons in mice exposed to prenatal methadone. Methadone is a synthetic μ-opioid agonist used for opioid maintenance therapy and chronic pain management. Methadone treatment for opioid use disorder in pregnant women can result in structural changes within the brain of their offspring causing and developmental delays to their children, including poorer motor performance. Using a mouse model of prenatal methadone exposure (PME), whole-cell electrophysiology, and analyses of cellular morphology, I elucidated the effects of PME on primary motor cortex (M1) output layer 5 (L5) neurons, which encompass the major cortical output pathway for motor control. My findings provide the first evidence that PME disrupts neuronal firing, subthreshold properties, and strength of local inputs onto M1 L5 neurons in prepubescent mice. / 2023-05-05

Primary somatosensory cortex (SI) is an important cortical structure involved in receiving and relaying sensory inputs to condition primary motor cortex (M1). The functional interaction between SI and M1 is important for motor control by providing surround inhibition, which is the inhibition of muscles not involved in the movement and in learning new motor skills. This interconnection is known as short-latency afferent inhibition (SAI) and may be probed using Transcranial magnetic stimulation and peripheral nerve stimulation. SAI is dependent on the afferent volley as increasing the nerve stimulation intensity increases the depth of SAI. Individuals with spinal cord injury show reductions in SAI evoked in lower limb and this may be a contributing factor to the impairments in motor control seen within this population. SAI has yet to be investigated in the upper limb in individuals with chronic cervical SCI and this thesis examines these alterations. Two experiments were performed examining M1 excitability (motor evoked potentials), SI excitability (somatosensory evoked potentials) and the interconnection between SI and M1 (SAI). The first Experiment investigated alterations in these measures in individuals with SCI while the second Experiment investigated these measures as a function of the afferent volley. The collective results from Experiment 1 indicate that motor evoked potentials and SAI are reduced but somatosensory evoked potentials are similar to controls. Further data from Experiment 2 indicate that SAI and SEPs increase as a function of the afferent volley and indicate that alterations seen in individuals with SCI may be due to cortical plasticity in the synapses from SI to M1 or within M1. The novel findings of this thesis have indicated aberrant cortical circuits in individuals with SCI and have indicated potential synapses that may be targets for TMS plasticity protocols to alter and restore function to these circuits. / Thesis / Master of Science (MSc)