Cortical Interneurons Differentially Regulate the Effects of Acoustic Context.

Both behavioral and neural responses to sounds are generally modified by the acoustic context in which they are encountered. As an example, in the auditory cortex, preceding sounds can powerfully suppress responses to later, spectrally similar sounds-a phenomenon called forward suppression (FWS). Whether cortical inhibitory networks shape such suppression or whether it is wholly regulated by common mechanisms such as synaptic depression or spike frequency adaptation is controversial. Here, we show that optogenetically suppressing somatostatin-positive (Sst+) interneurons weakens forward suppression, often revealing facilitation in neurons that are normally forward-suppressed. In contrast, inactivating parvalbumin-positive (Pvalb+) interneurons strengthens forward suppression and alters its frequency dependence. In a simple network model, we show that these effects can be accounted for by differences in short-term synaptic dynamics of inputs onto Pvalb+ and Sst+ interneurons. These results demonstrate separate roles for somatostatin and parvalbumin interneurons in regulating the context dependence of auditory processing.