Distinct Neural Mechanisms of Visual and Sound Adaptation in the Cat Visual Cortex.

Sensory areas exhibit modular selectivity to stimuli, but they can also respond to features outside of their basic modality. Several studies have shown cross-modal plastic modifications between visual and auditory cortices; however, the exact mechanisms of these modifications are yet not completely known. To this aim, we investigated the effect of 12 min of visual versus sound adaptation (referring to forceful application of an optimal/nonoptimal stimulus to a neuron[s] under observation) on the infragranular and supragranular primary visual neurons (V1) of the cat (Felis catus). Previous reports showed that both protocols induced orientation tuning shifts, but sound increased the bandwidths. Here, we compared visual versus sound adaptation effects, specifically analysing the firing changes and variability (computed as Fano factor) for raw and centred (around optimal orientation) tuning curves. We report that, compared with visual adaptation, sound adaptation elicited broader tuning curves in supragranular and infragranular layers accompanied with decreased variability in both cortical layers. This decreased variability may reflect stabilization of neural responses through enhanced inhibitory control or synaptic efficacy in local circuits. These findings suggest unique modulation of neural responses by distinct adaptation protocols, resulting in disparate tunings. We suggest that broader tuning curves and decreased response variability after sound adaptation may keep the visual cortex prepared across a spectrum of abstract representations that match with visual stimuli.