Functional thalamocortical innervation of VIP- and SST-expressing GABAergic interneurons in mouse barrel cortex.

In sensory cortices, conscious perception of stimuli involves a complex interplay of excitatory and inhibitory circuits. The subcortical source of sensory information is the thalamus, which in the whisker system houses (1) the "lemniscal" ventral posteromedial nucleus (VPM) and (2) the "paralemniscal" medial part of the posterior nucleus (POm). How much these two complementary inputs can drive feedforward inhibition in cortical layers by synapsing on GABAergic neurons is still incompletely understood. Here, we used optogenetics to study the incidence of VPM and POm projections to vasoactive intestinal polypeptide (VIP)- and somatostatin (SST)-expressing interneurons in barrel cortex. By using sensitive stimulation and recording methods, we show that VIP and SST neurons receive an extensive input, largely independent of laminar location or various cellular properties. Thus, thalamus-mediated feedforward inhibition is implemented in the circuit motifs of probably all VIP and SST interneurons, which they might differentially use, dependent on specific whisking behaviors.