Similarity of direction tuning among responses to stimulation of different whiskers in neurons of rat barrel cortex.

Cells in the rat barrel cortex exhibit stimulus-specific response properties. To understand the network mechanism of direction selectivity in response to facial whisker deflection, we examined direction selectivity of neuronal responses to single- and multi-whisker stimulations. In the case of regular-spiking units, i.e., putative excitatory cells, direction preferences were quite similar between responses to single-whisker stimulation of the principal and adjacent whiskers. In multi-whisker stimulation at short (< or = 5 ms) interstimulus intervals (ISIs), response facilitation was evoked only when the whiskers were deflected to the preferred direction of the response to the single whisker stimulation. These results suggest that there are neuronal networks among cells with different whisker preferences but with a common direction preference that could be the neuronal basis of the direction-selective facilitation of the response to multi-whisker stimulation. In contrast, multi-whisker stimulation at long (> or = 6 ms) ISIs caused non-direction-selective suppression of the response to the second stimulus. In the case of fast-spiking units, i.e., putative inhibitory cells, poor direction selectivity was exhibited. Thus stimulus direction is represented as the direction-selective responses to the single- and multi-whisker stimulations of putative excitatory cells rather than those of putative inhibitory cells.