Figure 7.

Mechanisms for sharpening response selectivity. (a) The membrane potential threshold for spike generation implies that even stimuli that elicit a significant depolarization may not elicit spiking, thereby sharpening the response to optimal stimuli. This is demonstrated in the temporal response to drifting gratings of varying orientation (left) and the corresponding orientation tuning curves (right) for membrane potential (top) and spikes (bottom). Panel a adapted from Liu et al. (2011). (b) The tuning of inhibitory synaptic conductances is broader than that of excitatory (E) synaptic conductances (top). The relative dominance of inhibition at nonpreferred orientations suppresses responses at these orientations and sharpens selectivity (bottom). Panel b adapted from Liu et al. (2011). (c) Visual input at the preferred orientation elicits dendritic bursts (top). This leads to greater orientation selectivity relative to when active conductances underlying dendritic bursts are suppressed (bottom). Panel c adapted from Smith et al. (2013).