Mapping the functional connectome of the claustrum: Noise filtering via local inhibitory circuits

We optogenetically mapped the function and spatial organization of inhibitory circuits formed by interneurons (INs) within the claustrum, a highly interconnected but poorly understood brain region. INs expressing parvalbumin or somatostatin attenuate claustrum output by inhibiting projection neurons (PNs), while INs expressing vasoactive intestinal peptide promote claustrum output by disinhibiting PNs. The spatial organization and degree of convergence differ for each interneuronal circuit. A computational model incorporating measured circuit properties predicts that differential inhibition of PNs by INs toggles claustrum output between cortical and subcortical brain regions and that the spatial organization of IN circuits nonlinearly filters claustrum output according to the strength and spatial distribution of excitatory input. Experimental measurements show that the claustrum spatially filters cortical input as predicted by the model. We conclude that the organization of its inhibitory circuits allows the claustrum to serve as a filter that improves the signal-to-noise ratio of signals transmitted to its downstream targets.