Figure 5.

Gain control through feedforward inhibition. (a) Stimuli of increasing contrast elicit larger synaptic depolarization of the membrane potential (Vm) and higher spike frequencies, yet the underlying synaptic excitatory (E) and inhibitory (I) currents increase proportionally, and even the weakest contrasts elicit both excitation and inhibition. (b) The change in spike rate (top) and excitatory and inhibitory currents (bottom) as a function of contrast. The proportional increase of excitation and inhibition prevents runaway excitation as stimulus contrast increases. Panels a and b adapted from Adesnik (2017). (c) Increasing stimulus contrast results in a multiplicative increase in response of excitatory neurons (E response) across the orientation tuning curve while leaving selectivity unchanged, i.e., a gain change. (d) Parvalbumin (PV) inhibitory neurons pool excitatory inputs tuned to different orientations, resulting in nonselective orientation tuning. Panel d adapted from Bock et al. (2011). (e) The response of excitatory neurons to stimuli of different orientations is modulated by the activity of PV neurons. Because PV neurons are reciprocally connected with the local excitatory population, their activity can provide multiplicative gain control that mimics the effects of varying contrast. Panel e adapted from Atallah et al. (2012).