Optogenetic Stimulation Shifts the Excitability of Cerebral Cortex from Type I to Type II: Oscillation Onset and Wave Propagation
Optogenetically induced gamma band (40–60 Hz) oscillations in primate motor cortex, redrawn from .
A: Gamma oscillations in the local field potentials at five recording sites on the microelectrode array for subject T. The oscillation phase has a spatial gradient that indicates wave propagation. Black dots indicate the peaks of one gamma cycle across neighboring electrodes; B: Optogenetic stimulation induces expanding waves, as summarized in the phase-triggered average of gamma (40–110 Hz) spatial field potential, based on the phase of the optogenetically-induced 50 Hz gamma oscillation. The dot indicates the point where the fiber optic light source was surgically inserted. The tip of the optical fiber was likely slanted to the right of this point, corresponding to the origin of the waves. C: Trial-averaged spectrogram of the local field potential when the optical stimulation was ramped from 0 mW to 6 mW over 4 seconds. The mean power within each frequency band for the 500 ms preceding stimulation was subtracted (in dB) from the power during stimulation to enhance visualization of the optogentically-induced changes. D: Power of the oscillations in the local field potential during the ramp protocol.