Emergent Properties of Tactile Scenes Selectively Activate Barrel Cortex Neurons

Abstract

Rats discriminate objects by scanning their surface with the facial vibrissae, producing spatiotemporally complex sequences of tactile contacts. The way in which the somatosensory cortex responds to these complex multivibrissal stimuli has not been explored. It is unclear yet whether contextual information from across the entire whisker pad influences cortical responses. Here, we delivered tactile stimuli to the rat vibrissae using a new 24 whisker stimulator. We tested sequences of rostrocaudal whisker deflections that generate multivibrissal motion patterns in different directions across the mystacial pad, allowing to disambiguate local from global sensory integration. Unitary electrophysiological recordings from different layers of the barrel cortex showed that a majority of neurons has direction selectivity for the multivibrissal stimulus. The selectivity resulted from nonlinear integration of responses across the mystacial pad. Our results indicate that the system extracts collective properties of a tactile scene.

Late Emergence of the Vibrissa Direction Selectivity Map in the Rat Barrel Cortex

“…Activity-dependent plasticity has indeed been demonstrated in SIbf both at the cellular level (Glazewski and Fox, 1996;Jacob et al, 2008) and at the scale of the entire barrel (Feldman and Brecht, 2005;Frostig, 2006). Sensory activity is known to shape and strengthen most sensory cortical maps such as those for ocular dominance in the rodent visual cortex (Berardi et al, 2000;Smith and Trachtenberg, 2007) or for orientation and direction selectivity in the cat and ferret visual cortex (Crair et al, 1998;Li et al, 2008).…”

“…Neurons in SIbf (primary somatosensory cortex, barrel field) are known to have their activity modulated by numerous parameters. In addition to their tuning to the principal vibrissa identity (the barrel map), some neurons preferentially respond to specific directions of vibrissa deflections (Bruno et al, 2003;Lee and Simons, 2004), to high-frequency vibrations (Andermann et al, 2004), or to the apparent global motion of objects through the vibrissa pad (Jacob et al, 2008). However, no superposition of functional maps has been reproducibly observed in SIbf.…”

Ce que les vibrisses disent au cerveau tactile

“…Cependant, lorsque les 25 vibrisses sont corrélées, la réponse informations en provenance de plusieurs vibrisses simultanément ou en léger décalage temporel. Ainsi, les neurones du cortex à tonneaux répondent préférentiellement à certaines séquences spatio-temporelles de stimulations multivibrissales impliquant de nombreuses vibrisses en s'écartant fortement des prédictions d'un simple modèle linéaire [7,[16][17][18].…”

“…Nous avons trouvé qu'une majorité de neurones montrent une sélectivité marquée pour une direction donnée de déplacement de la barre. Cette sélectivité est probablement soustendue par des connexions intracorticales latérales [18,20]. Ainsi, au contraire de la vision classique linéaire de l'organisation du système vibrisse-cortex à tonneaux, le cortex semble intégrer simultanément l'information tactile sur la totalité de la matrice mystaciale des vibrisses, assurant ainsi l'implémentation d'une analyse contextuelle de l'information tactile.…”

Coding of Apparent Motion in the Thalamic Nucleus of the Rat Vibrissal Somatosensory System

“…Details of the whisker stimulation protocols have been described previously (Jacob et al, 2008). Briefly, each whisker was cut to a length of 10 mm and inserted into a short plastic tube glued to a piezoelectric bender (Polytec-PI).…”