Spectral analysis of whisking output via optogenetic modulation of vibrissa cortex in rat.

Whisking motor output in awake and freely moving rat is investigated with optogenetic excitation/inhibition of the vibrissae motor cortex (vMCx) layer V. The goal of the study is to establish the direct causal relationship between the cortical activity and the whisking output using optical stimulation, excitatory or inhibitory, with different frequencies. Progression and reduction of the whisking frequency was obtained; however, the whisking frequency did not necessarily followed the entrainment stimulus. Based on our observations, the excitation of the vMCx doubled and inhibition reduced the whisking frequency to half, compared to control, at all stimulus frequencies. This result is an empirical evidence that the cortex exerted control through a central pattern generator structure since complete inhibition was not obtained and the frequency of the response was different from that of the stimulus. We suggest that the use of the optogenetic approach, which enabled us to perform the bidirectional modulation and direct readout from vMCx, has brought valid evidence for the causal connection between cortical activity and whisking motor output.