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Game theory outlines optimal response strategies during mixed-strategy competitions in which available actions are selected probabilistically. The neural processes involved in choosing individual strategic actions, however, remain poorly understood. Here, actions need to be selected (1) in the absence of sensory instruction or reward cues and (2) independent of previous events. This thesis examines the neural processes involved in action selection during mixed-strategy competition. To do so, we both measured and manipulated presaccadic activity in the primate superior colliculus (SC), a structure involved in the generation of orienting saccadic eye movements, during a strategic game. The first study tested whether the SC is involved in choosing saccades under strategic conditions. Monkeys were free to choose either of two saccade targets as they competed against a computer opponent during the mixed-strategy game ‘matching-pennies’. The accuracy with which pre-saccadic SC activity predicted upcoming choice gradually increased in the time leading up to the saccade. Probing the SC with supra-threshold stimulation demonstrated that these evolving signals were functionally involved in preparing strategic saccades. Finally, sub-threshold stimulation of the SC increased the likelihood that contralateral saccades were selected. In the second study, we compared the influence of previous actions and rewards on updating premotor activity in the SC in the strategic condition where eliciting stochastic responses was optimal and in a non-strategic condition where stochastic responses were also elicited but through explicit instruction. To avoid exploitation by opponents during mixed-strategy competitions one should select behaviors unpredictably, that is, independent of previous choices and their outcomes. The iterative updating of neural processes involved in selecting actions to produce mixed-strategy behaviors, however, remain poorly understood In both tasks, premotor activity and behavior were shaped by past actions and rewards with more recent events exerting the largest influence. Importantly, these sequential effects were attenuated under strategic conditions suggesting that updating of selection processes is not entirely automatic but can be tailored to different decision-making contexts. Together our results highlight the active role played by the brain in choosing strategic actions. / Thesis (Master, Neuroscience Studies) -- Queen's University, 2009-01-30 17:11:21.002

Durant les dernières décennies, le système moteur a été largement étudié. Pourtant, bien des zones d'incertitudes persistent concernant d'une part la nature des circuits neuronaux de haut niveau impliqués dans l'émergence des sentiments d'intention ou de conscience motrice et d'autre part l'organisation des structures cérébrales de bas-niveau impliquées dans l'expression de ces sentiments. Il a été suggéré que le cortex pariétal et l'aire motrice supplémentaire pourraient jouer un rôle dans la génération des intentions motrices, alors que le cortex prémoteur pourrait plutôt sous-tendre la conscience du geste. Cela étant, les processus exacts implémentés dans chacune de ces régions, la façon dont elles interagissent fonctionnellement et la nature des signaux qu'elles échangent avec les structures sensorimotrices considérées de bas-niveau demeurent méconnus. Il est établi que ces structures bas-niveau, dont le cortex moteur primaire et le cervelet, contiennent des cartes sensorimotrices organisées de manière topographique. Cependant, l'organisation fine de cette topographie et la nature des interactions entre les différentes cartes restent à définir. Dans ce travail de thèse, j'ai utilisé la stimulation électrique directe chez des patients opérés de tumeurs et malformations cérébrales pour explorer la manière dont les multiples représentations motrices sont organisées et pour identifier les régions responsables de l'émergence des sentiments d'intention et de conscience motrice. J'ai alors pu montrer, en particulier, l'existence de cartes motrices multiples au sein des cortex moteur primaire et cérébelleux. Par ailleurs, j'ai pu identifier le rôle critique du cortex pariétal pour l'émergence du sentiment d'intention motrice et -sur la base de processus prédictifs- de la conscience d'agir. Par rapport à ce point, j'ai aussi pu mettre en évidence que le cortex prémoteur était impliqué, à travers un contrôle continu des prédictions pariétales, dans l'émergence d'une conscience d'agir non plus inférée mais véritable / During the last five decades, the motor system has been widely studied. Yet, little is known about the neural substrate of high-level aspects of movement such as intention and awareness and how these functions are related to low-level movement execution processes. It has been suggested that the parietal cortex and supplementary motor area are involved in generating motor intentions, while premotor cortex may play a role in the emergence of motor awareness. However, the precise mechanisms implemented within each of these areas, the way they interact functionally and the nature of the signals conveyed to primary sensory and motor regions is far from being understood. Furthermore, intention and awareness of movement are also influenced by peripheral information coming from the skin, muscles and joints, and this information must be integrated to produce smooth, accurate and coordinated motor actions. Cortical and subcortical structures such as the primary motor cortex and the cerebellum are known to contain motor maps thought to contribute to motor control, learning and plasticity, but the intrinsic organization of these maps and the nature of their reciprocal relations are still unknown. In this thesis I used Direct Electrical Stimulation in patients undergoing brain surgeries to investigate how multiple motor representations are organized and identify the regions responsible for the emergence of conscious motor intention and awareness. I showed, in particular, the existence of multiple efferent maps within the cerebellum and the precentral gyrus. Furthermore, I identified the critical role of the parietal cortex for the emergence of conscious intention and -based on predictive processes- motor awareness. I also provided evidence that the premotor cortex is involved in "checking" parietal estimations, thus leading to a sense of "veridical awareness"

Il NM è una disturbo del movimento spontaneo caratterizzato da un sottoutilizzo dell’arto controlesionale in assenza di un deficit primario che migliora con il comando verbale. Per la sue caratteristiche è difficile da evocare in ambito clini-co e il suo riconoscimento si basa sull'osservazione dei sintomi. Le lesioni associate al NM sono diverse e i suoi mecca-nismi sono sconosciuti. La compromissione selettiva del movimento spontaneo suggerisce un coinvolgimento del si-stema motorio mediale. La ricerca ha lo scopo di studiare il NM con un nuovo metodo quantitativo, basato su actigra-fia, e di esplorare le basi neuroanatomiche. Due accelerometri erano posti su entrambi i polsi per 24 ore. 31 soggetti sani e 38 cerebrolesi, 6 con MN sono stati reclutati. In due casi abbiamo esplorato le lesioni. E’stato validato il nuovo indice di asimmetria AR24h. I MN mostravano un comportamento asimmetrico, simile agli emiplegici e diverso dai sani e dai pazienti non emiplegici. I pazienti mostravano una lesione del cingolo e putamen, parti del sistema motorio mediale, importante per le azioni volontarie. I risultati che l’actigrafia differenziale nel quantifica il movimento spontaneo e valuta il NM. Putamen e il cingolo causano una disfunzione del sistema motorio mediale e induce NM. / The MN is a movement disorder characterized by spontaneous underutilized contralesional limb in the absence of a primary deficit that improves with the verbal command. For its characteristics it is difficult to evoke in the clinical set-ting and its recognition is based on observation of symptoms. The lesions associated with NM are different and its mechanisms are unknown. The selective impairment of spontaneous movement suggests the involvement of the medi-al motor system. Research has the aim of studying the MN with a new quantitative method, based on the actigraphy, and to explore the neuroanatomical bases. Two accelerometers were placed on both wrists for 24 hours. Sog-31 jets and 38 brain-healthy, with 6 MN were recruited. In two cases we analysis lesions. It has been validated new asymmetry index AR24h. The MN showed an asymmetric behavior, similar to and different from the healthy and hemiplegic pa-tients not hemiplegic. Patients showed a lesion of the cingulate and putamen, parts of the medial motor system im-portant for voluntary actions. The differential actigraphy quantifies the spontaneous movement and evaluates the NM. Putamen and the track cause dysfunction of the motor system and causes medial NM.

Ce travail s'intéresse à l'organisation fonctionnelle du système sensorimoteur. La somatotopie est une caractéristique essentielle de M1, mais l'organisation fonctionnelle des autres aires motrices (PM, SMA, et IPL) n'est pas encore clairement établie. Premièrement, nous avons exploré par IRMf l'organisation fonctionnelle sensorimotrice chez des sujets sains exécutant des mouvements simples. Nos résultats montrent que les représentations motrices sont organisées selon des synergies musculaires et qu'une organisation somatotopique, différente de celle de M1, existe dans l'IPL. Bien qu'elle fasse régulièrement l'objet de critiques, la DES est à la base de la plupart de nos connaissances sur le cortex moteur, que confirme les études en IRMf. Ainsi, en réponse au débat en cours, nous avons passé en revue les arguments récents confortant la confiance que nous pouvons accorder à la DES. Des études récentes concluent à l'implication du PPC dans l'intention motrice, mais le débat reste ouvert sur la relation entre intention et préparation motrices. Certains prétendent que l'intention serait le sous-produit de la préparation motrice, ne laissant aucune place à la volonté dans le contrôle moteur. Pour étudier cette question, nous avons mis en place une expérience comportementale, incluant des tâches de réaction simple et de Libet pour comparer les deux processus cognitifs. Nos résultats montrent que le temps de réaction entre intention interne et réaction motrice est égal à celui séparant commande externe et réaction motrice. Cela contredit donc l'affirmation selon laquelle la préparation motrice précèderait l'intention et donc que l'intention émergerait du processus d'intention motrice / In this thesis, I am interested in the functional organization of human cortical sensorimotor system. Somatotopy is the prominent structure of the functional organization in sensory and motor cortex. However, the structure of the functional organization in higher order motor area, such as IPL is little known. Therefore, in the first part, I study the functional organization of human sensory- and motor- related brain regions using fMRI, by guiding healthy subjects to perform simple repetitive movements of different body parts. Our results demonstrate that, 1) motor synergy is the neural basis represented in the motor cortex; and 2) somatotopic organization also exists in IPL but with different structure from that of sensorimotor cortex. Despite continuous criticism on DES, most of our primitive knowledge of the sensorimotor cortex comes from DES studies, and our fMRI result supports the findings of DES. In response to the ongoing debate on DES, in the second study, we review recent evidence to re-establish the confidence on DES. Accumulating evidence indicates that PPC is related to the emergence of motor intention. However, debate on the relation between motor intention and preparation never stops, some claims that motor intention is the byproduct from motor preparation, thus denying the volition of human motor control. Besides this complexity, we design a straightforward behavior experiment, including simple reaction task and Libet task, in order to compare the cognitive process of motor preparation and motor intention. Our result shows that RT from internal motor intention to motor output is equal to the RT from external cue to motor output, thus rejecting the possibility that motor preparation starts in advance of motor intention and doesn't support that motor intention arises from the process of motor intention