Spatial organization of neurons coding for complex multi-whisker features in S1bf

Orateur : Laurent BOURDIEU (Laboratoire de Neurobiologie Moléculaire et Cellulaire, CNRS UMR 8544, Ecole Normale Supérieure, Paris)

During exploration of their environment, rats contact objects with multiple whiskers in a complex spatio-temporal pattern. Recent electrophysiology experiments (Estebanez et al., 2012, Nat. Neurosc., 15(12), 1691-1699) have demonstrated, using multi-whisker sensory stimulations, the existence in layers 4/5 of rat primary somato-sensory cortex (SIbf), of “global” neurons that encode correlated deflections of all whiskers and “local” neurons that detect local deflections of individual whiskers. Local neurons optimally detect angular contrast between the principal whisker and the surrounding ones. We have used two-photon fluorescence microscopy (TPFM) to explore the existence of similar neuronal categories in the supra-granular layers of the SIbf, and the potential functional maps associated with these newly described tuning functions. A 25-whisker stimulator that allows the stimulation of each whisker in all directions (2D) and with a 1kHz bandwidth (Jacob et al., 2010, JNM 189:65–74) was combined with a TPFM to record optically the sensory-evoked cortical activity. We found that among all the neurons present in layers 2/3 in SIbf, less than a half was responding to any of our whisker stimulations. A majority of the responding neurons were activated by uncorrelated whisker deflections, but we observed a small fraction of neurons responding only to the correlated deflection of all whiskers at a time. These neurons share similar properties with the global neurons described in layer 4/5 by Estebanez et al. By combining the functional imaging with 50 µm-resolution post-mortem histology, we additionally demonstrate that local-like and global-like neurons are spatially segregated in layer 2/3, following the barrel/septum organization. This spatial segregation might have important consequences on their respective functional roles in sensory processing.

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