Les rongeurs utilisent leurs vibrisses pour sonder tactilement leur environnement. Tout contact induit des contraintes mécaniques lentes quasi-statiques et rapides vibratoires, qui se propagent jusqu'en base de vibrisse où des mécanorécepteurs dédiés les détectent. C'est cette étape de transduction mécanique de l'information tactile opérée par les vibrisses, avant tout codage neuronal,que nous avons étudiée.En combinant expériences biomimétiques et modélisations, nous avons cherché à isoler les contributions relatives des composantes lentes et rapides pour la détection etlocalisation d'objets, et la perception de textures. Un des enjeuxétait de comprendre ce qui d'un point de vue mécanique confère aux rongeurs leur rapidité et acuité remarquables. Pour cela, nous avons d’abord étudié la dynamique de choc vibrisse-objet, et montré que la position radiale de l’objet pouvait être encodée à la fois dans le taux de variation de la composante quasi-statique du moment en base et dans l’amplitude et la fréquence des vibrations induites. En mimant le mouvement de whisking, nous avons de plus montré qu’utiliser la composante vibratoire permet aux rongeurs une détection des contacts plus rapide et plus robuste. Nous avons ensuite étudié la perception de textures élémentaires, et montré que la variation maximale du moment en base dépendait de manière univoque de leur taille. Des expériences sur rats anesthésiés combinant suivi des vibrisses et mesures d’activité neuronale dans le cortex nous ont enfin permis de proposer un mécanisme d’encodage des textures où la topographie de la surface est modulée par les propriétés de vibrations de la vibrisse et démodulée au niveau neuronal. / Rodents use their facial whiskers to probe their environment by touch. Any contact induces both slow quasi-static and fast vibratory mechanical stresses that propagate down to the base of vibrissae where dedicated mechanoreceptors detect them. It is this phase of mechanical transduction of the tactile information operated by the whiskers, prior to any neural coding, that we have studied here. By combining biomimetic experiments and theoretical modeling, we have sought to separate the relative contributions of both slow and fast components, for the detection and localization of objects, as well as the perception of textures. One of the challenges of this work was to understand what determines from a mechanical point of view, rodents remarkable temporal and spatial precision.For this, we have first studied the shock dynamic between a whisker and an object and shown that the radial position of the object could be encoded both in the rate of change of the quasi-static component of the base torque as well as in the amplitude and frequency of the induced vibrations. In addition, by mimicking the whisking mode adopted by rodents, we have shown that using the vibratory component allows rodents to detect contacts faster and more robustly.We then studied the perception of elementary textures and showed that the maximum variation of the base torque depends univocally on their size. Experiments on anesthetized rats, combining whisker optical tracking and cortical neural activity measurements, led us to propose an encoding mechanism of texture perception where the surface topography is modulated by the vibration properties of the whiskers and demodulation occurs at a neuronal level.

Submitted by Automa??o e Estat?stica (sst@bczm.ufrn.br) on 2017-02-22T18:57:02Z No. of bitstreams: 1 JosephAndrewsBeloAlves_DISSERT.pdf: 2493249 bytes, checksum: 1b737b22d98e824d63c44e7fc7f94b62 (MD5) / Approved for entry into archive by Arlan Eloi Leite Silva (eloihistoriador@yahoo.com.br) on 2017-03-04T00:26:10Z (GMT) No. of bitstreams: 1 JosephAndrewsBeloAlves_DISSERT.pdf: 2493249 bytes, checksum: 1b737b22d98e824d63c44e7fc7f94b62 (MD5) / Made available in DSpace on 2017-03-04T00:26:10Z (GMT). No. of bitstreams: 1 JosephAndrewsBeloAlves_DISSERT.pdf: 2493249 bytes, checksum: 1b737b22d98e824d63c44e7fc7f94b62 (MD5) Previous issue date: 2016-08-17 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior (CAPES) / Ao explorar ativamente o ambiente, ratos exibem comportamentos sens?rio-motores r?tmicos com frequ?ncia na faixa teta (5-10 Hz). Dentre esses est?o o sniffing (respira??o ativa e r?pida), o whisking (movimento das vibrissas faciais) e as vocaliza??es ultrass?nicas. Estudos recentes mostraram formas de sincronicidades entre tais ritmos: a protra??o e retra??o das vibrissas est?o associadas em fase, respectivamente, ? inala??o e exala??o respirat?ria; a constri??o das cordas vocais necess?ria para a produ??o vocal, por sua vez, est? condicionada ? fase exalante do sniffing e de retra??o do whisking. Embora essas e outras observa??es indiquem uma intera??o entre ritmos e geradores de padr?es no tronco encef?lico aos quais s?o atribu?dos os movimentos orais, faciais e respirat?rios. Com o intuito de adquirir melhor compreens?o acerca das hierarquias concernentes aos circuitos neurais envolvidos em tais atividades, n?s gravamos simultaneamente o whisking, sniffing e as vocaliza??es em ratos durante livre explora??o social. Para este prop?sito, oito eletrodos foram inseridos cirurgicamente para a aquisi??o de sinais eletromiogr?ficos bilaterais dos m?sculos que controlam as vibrissas e uma c?nula foi implantada por meio de uma perfura??o no osso nasal para o registro do ciclo respirat?rio. Ap?s recupera??o e habitua??o, dois ratos (um implantado e outro de est?mulo) foram posicionados sobre duas plataformas separadas por uma fenda onde possibilitava a explora??o m?tua dos animais. Esses epis?dios foram filmados atrav?s de uma c?mera de alta velocidade (250 Hz) para a captura dos movimentos das vibrissas. As vocaliza??es ultrass?nicas foram detectadas por um microfone suspenso. N?s conduzimos an?lises de fase e frequ?ncia para validar os sinais registrados e caracterizar as a??es rec?procas entre esses ciclos em contextos sociais. Os resultados confirmaram que ambos o whisking e o sniffing ocorrem em turnos nas frequ?ncias teta durante explora??o social. Al?m disso, a esperada rela??o em anti-fase entre os sinais dos grupos musculares que controlam a protra??o e retra??o das vibrissas assim como a forte sincronia com o ciclo respirat?rio foram observadas. Interessantemente, nossos dados sugerem que esta sincronia ? imediatamente dissipada durante a emiss?o de vocaliza??es ultrass?nicas. Em vez disso, n?s presenciamos um novo comportamento de whisking, que consiste em retra??o e protra??o ativas e independentes do ciclo respirat?rio. / When actively exploring the environment, rats exhibit several rhythmic behaviors with frequencies in the theta range (5-10 Hz). These include sniffing (active fast respiration), whisking (movement of the facial vibrissae), and ultrasonic vocalizations. Synchronizations between each pair of these behaviors have been observed in recent studies: vibrissae protraction-retraction is linked to the inhalation-exhalation phase of breathing; constriction of the vocal folds for vocalization, in turn, is locked to the exhalation phase of sniffing; accordingly, vocalizations were observed to synchronize with the retraction phase of whisking. These and other observations point to an interaction of rhythm and pattern generators in the brainstem controlling the coordination of respiratory, oral and facial movements. To better understand the hierarchies among these circuits we simultaneously recorded sniffing, whisking and vocalizations from rats during free social exploration. For this purpose, eight electrodes were inserted surgically to acquire bilateral EMG signals from muscles controlling the protraction and retraction of the whiskers and a cannula was implanted through the nasal bone to record the respiratory cycle. After one week of recovery and habituation, two rats (one implanted and one naive) were placed across a gap where they could explore each other. These interactions were filmed with a high speed camera (250 Hz) to capture whisker movements and ultrasonic vocalizations were recorded from an overhanging microphone. We made frequency and phase analysis to validate the recorded signals and characterize the interplay between these sensorimotor rhythms. Results confirmed that both sniffing and whisking occur in bouts at theta frequencies during social exploration. Furthermore, we observed the expected anti-phase relationship between the EMGs from muscles controlling whisker protraction and retraction as well as their tight synchrony with the sniffing cycle. Interestingly, our data suggests that this synchrony is immediately lost during the emission of ultrasonic vocalizations. Instead, we observed a novel whisking behavior, consisting of active vibrissae protraction and retraction independent of the respiratory cycle.

La connaissance des mécanismes physiologiques de la perception sensorielle nécessite la compréhension de la manière dont le système nerveux central récolte et traite le flux de stimuli sensoriels qui le bombardent en permanence. Il est essentiel de caractériser de manière précise : 1) les stratégies d'exploration qu'utilise le rat pour positionner ses vibrisses par rapport à son environnement et 2) la manière dont ces organes senseurs produisent et transmettent un signal mécanique pertinent pour les mécanorécepteurs situés à la base de la vibrisse. Dans une première partie, nous avons trouvé que l'amplitude du whisking chez le rat en comportement décroit avec la vitesse de locomotion, tandis que les vibrisses sont globalement plus protractées quand l'animal court plus vite. Dans la seconde partie de la thèse, nous avons validé un modèle de transduction mécanique en comparant des prédictions théoriques avec des mesures expérimentales de déformations vibrissales. Ainsi nous avons pu décrire des événements dynamiques rapides ayant lieu après un choc sur un objet, ainsi que la propagation de ces ondes de déformation le long de la vibrisse jusqu'au follicule. D'autre part nous avons mis en évidence, suite à la stimulation d'une vibrisse, des mouvements d'une adjacente. Dans la dernière partie, nous avons mesuré et caractérisé les oscillations rapides induites par le glissement de la vibrisse sur une texture de topographie contrôlée. Nous avons rejoué ces déformations vibrissales en enregistrant concomitamment l'activité neuronale dans le cortex somatosensoriel. Nous avons montré qu'il existe une corrélation entre l'enveloppe de ces oscillations rapides et la réponse corticale.

<p dir="ltr">Localizing movements in the external space is crucial for animals to navigate safely, find food, avoid predators, and interact with their surroundings. Efficient localization during body movements requires the brain to distinguish between externally generated movements and self-generated ones. This involves integrating external stimulation with a continuous estimate of one's body position, to isolate external motion by suppressing sensations arising from self-motion.</p><p dir="ltr">To explore the neural mechanisms underlying object localization during active touch, we focused on the mouse superior colliculus (SC), which harbors multiple egocentric maps of sensorimotor space. Our studies revealed that SC neurons exhibit a rapidly adapting tactile response during externally generated touch. The response is significantly attenuated during self-generated touch, thus enhancing the ability to distinguish between external and self-induced tactile stimuli. Additionally, the direction of external motion is precisely encoded in the firing rates of these tactile-responsive neurons, indicating a specialized localization mechanism within the SC.</p><p dir="ltr">In scenarios devoid of external stimuli, SC neural activity accurately reflects the kinematics of self-motion, such as whisker position and locomotion speed, capturing past, present, and future body positions. Half of the neurons that encode self-motion also respond to external tactile stimuli. This dual functionality suggests that these neurons not only track self-motion but also engage in the processing of external tactile information. The magnitude of the external tactile response in these neurons is modulated by the state of self-motion upon touch. These results suggest that SC neurons integrate internal estimates of body movements with external tactile inputs to compute the egocentric distance of objects.</p>