Neurosurgery is an effective method for prolonging life and improving outcomes for patients with brain tumors. However, this option bears the risk of damaging areas of eloquent cortex, areas associated with motor and language tasks that, when lesioned, will result in a functional deficit for the patient. Functional magnetic resonance imaging (fMRI) is a valuable tool in the localization of eloquent cortex for preoperative neurosurgical planning. Through use of this modality of functional neuroimaging, the neurosurgeon can adjust the surgical trajectory to incur the least amount of damage to sites of functional activity. The supplementary motor area (SMA) is one such site of eloquent cortex that must be visualized preoperatively due to the risk of postoperative deficit with lesions in this area. However, due to both the effects of tumor pathology and naturally occurring interindividual variability, the SMA’s location and functional fingerprint can be highly variable. We present a study in which patients with frontal tumor (n=46) underwent task-based fMRI for motor and language network mapping. The patient-specific functional data were normalized and evaluated using ROI analysis to illustrate group-level activation patterns within the SMA during the language and motor tasks. The results illustrate a distinct pattern of activation including a rostro-caudal organization of language and motor activation, overlapping extent cluster volumes throughout the two functional subdivisions of the SMA, the pre-SMA and SMA proper, and discrete activation foci.

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.

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No description available.

Cette thèse a pour thème l'étude les mécanismes neurocognitifs impliqués dans la détermination de la latéralité intrinsèque d'objets. Dans une première étude, nous avons montré qu'une projection de son propre schéma corporel sur un objet est nécessaire pour en différencier la gauche de la droite. Cette inscription corporelle fut observée aussi bien pour des stimuli humains que non humains, suggérant que la présence d'axes intrinsèques à l'objet est suffisante pour y permettre la projection du corps. Une seconde étude nous a permis de mieux comprendre les mécanismes neuronaux de l'inscription corporelle, en utilisant une tâche de comparaison de formes identiques ou miroir différemment orientées. Les stimuli étaient soit des corps humains, soit des assemblages de cubes. La magnetoencephalographie (MEG) révéla une implication du lobe pariétal supérieur gauche dans l'incarnation et la transformation spatiale des deux stimuli. Par ailleurs, une contribution de l'aire motrice supplémentaire fut observée dans le cas des cubes. Ainsi, nous proposons de considérer le lobe pariétal supérieur comme le substrat neural d'un émulateur utilisant le schéma corporel afin d'encoder la latéralité d'un objet et de prédire les conséquences visuelles d'une transformation spatiale. La contribution additionnelle de l'aire motrice supplémentaire a probablement facilité la transformation de formes non familières, par l'envoi d'une commande motrice à l'émulateur visant à accroître la cohérence de l'objet tourné mentalement. Ces interprétations supportent l'idée d'une cognition incarnée dans les actions corporelles. / The aim of this thesis was to study the neurocognitive mechanisms implicated in the determination of objects intrinsic handedness. In a first study, we evidenced that distinguishing the left from the right of an object requires a mental projection of the body schema onto the stimulus. This embodiment process occured for human and non human stimuli as well, suggesting that the mere presence of intrinsic axes on stimulus enables the bodily projection. In a second study, we explored the neural mechanisms underlying embodiment in a handedness shape matching task, using human bodies and cubes assemblies as stimuli with different orientations. Magnetoencephalography (MEG) revealed that the left superior parietal lobe participated in the embodiment and spatial transformation of both stimuli. In addition, we observed a contribution of the supplementary motor area for cube assemblies specifically. Therefore, we consider the superior parietal lobe as the neural substrate of an emulator processing the body schema to encode handedness and to predict the visual consequences of a spatial transformation. Besides, the additional contribution of the supplementary motor area probably helped the spatial transformation of unfamiliar shapes by backpropagating a motor command to the emulator to increase cohesiveness of the mentally rotated object. These interpretations support the grounding of cognition in bodily actions.

Performance of efficient and precise motor output requires proper planning of movement parameters as well as integration of sensory feedback. Peripheral sensory information is projected not only to parietal somatosensory areas but also to cortical motor areas, particularly the supplementary motor area (SMA). These afferent sensory pathways to the frontal cortices are likely involved in the integration of sensory information for assistance in motor program planning and execution. It is not well understood how and where sensory information from the limb contralateral to motor output is modulated, but the SMA is a potential cortical source as it is active both before and during motor output and is particularly involved in movements that require coordination and bilateral upper-limb selection and use. A promising physiological index of sensory inflow to the SMA is the frontal N30 component of the median nerve (MN) somatosensory-evoked potential (SEP), which is generated in the SMA. The SMA has strong connections with ipsilateral areas 2, 5 and secondary somatosensory cortex (S2) as well as ipsilateral primary motor cortex (M1). As such, the SMA proves a fruitful candidate to assess how sensory information is modulated across the upper-limbs during the various stages of motor output. This thesis inquires into how somatosensory information is modulated in both the SMA and primary somatosensory cortical areas (S1) during the planning and execution of a motor output contralateral to sensory input across the upper-limbs, and further, how and what effect ipsilateral primary motor cortex (iM1) has upon modulation of sensory inputs to the SMA.

Performance of efficient and precise motor output requires proper planning of movement parameters as well as integration of sensory feedback. Peripheral sensory information is projected not only to parietal somatosensory areas but also to cortical motor areas, particularly the supplementary motor area (SMA). These afferent sensory pathways to the frontal cortices are likely involved in the integration of sensory information for assistance in motor program planning and execution. It is not well understood how and where sensory information from the limb contralateral to motor output is modulated, but the SMA is a potential cortical source as it is active both before and during motor output and is particularly involved in movements that require coordination and bilateral upper-limb selection and use. A promising physiological index of sensory inflow to the SMA is the frontal N30 component of the median nerve (MN) somatosensory-evoked potential (SEP), which is generated in the SMA. The SMA has strong connections with ipsilateral areas 2, 5 and secondary somatosensory cortex (S2) as well as ipsilateral primary motor cortex (M1). As such, the SMA proves a fruitful candidate to assess how sensory information is modulated across the upper-limbs during the various stages of motor output. This thesis inquires into how somatosensory information is modulated in both the SMA and primary somatosensory cortical areas (S1) during the planning and execution of a motor output contralateral to sensory input across the upper-limbs, and further, how and what effect ipsilateral primary motor cortex (iM1) has upon modulation of sensory inputs to the SMA.

Deficits in interval timing have been described in focal brain lesions and in various neuropsychiatric disorders including Parkinson's disease (PD). The aim of this study was to explore brain areas responsible for human time perception and for the timing deficit in PD. We used a time reproduction task (TRT) which consisted of an encoding phase (during which visual stimuli of durations from 5 to 16.6 sec were presented) and a reproduction phase (during which interval durations were reproduced by a button pressing). In our first fMRI study, we used a parametric modulated analysis searching for brain areas with activity, expressed as Blood Oxygenation Level Dependent (BOLD) signal, correlated with the duration of time interval. During the encoding phase, there was a gradual deactivation of the left prefrontal cortex (PFC) and cingulate gyrus. During the reproduction phase, there was a gradual deactivation in precuneus and an accumulation of activity in the left PFC, primary motor area, right caudate and supplementary motor area (SMA). The second study aimed at supporting the role of two of these areas, SMA and precuneus in interval timing by repetitive transcranial magnetic stimulation (rTMS). Accuracy and variability of time estimates were compared before and after rTMS. Accuracy of estimates was not...

Deficits in interval timing have been described in focal brain lesions and in various neuropsychiatric disorders including Parkinson's disease (PD). The aim of this study was to explore brain areas responsible for human time perception and for the timing deficit in PD. We used a time reproduction task (TRT) which consisted of an encoding phase (during which visual stimuli of durations from 5 to 16.6 sec were presented) and a reproduction phase (during which interval durations were reproduced by a button pressing). In our first fMRI study, we used a parametric modulated analysis searching for brain areas with activity, expressed as Blood Oxygenation Level Dependent (BOLD) signal, correlated with the duration of time interval. During the encoding phase, there was a gradual deactivation of the left prefrontal cortex (PFC) and cingulate gyrus. During the reproduction phase, there was a gradual deactivation in precuneus and an accumulation of activity in the left PFC, primary motor area, right caudate and supplementary motor area (SMA). The second study aimed at supporting the role of two of these areas, SMA and precuneus in interval timing by repetitive transcranial magnetic stimulation (rTMS). Accuracy and variability of time estimates were compared before and after rTMS. Accuracy of estimates was not...