In various mental disorders, dysfunction of the prefrontal cortex contributes to cognitive deficits. Here we studied how the claustrum (CLA), a nucleus sharing reciprocal connections with the cortex, may participate in these cognitive impairments. We show that specific ensembles of CLA and of medial prefrontal cortex (mPFC) neurons are activated during a task requiring cognitive control such as attentional set-shifting, i.e. the ability to shift attention towards newly relevant stimulus-reward

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... ssociations while disengaging from irrelevant ones. CLA neurons exert a direct excitatory input on mPFC pyramidal cells, and chemogenetic inhibition of CLA neurons suppresses the formation of specific mPFC assemblies during attentional set-shifting. Furthermore, impairing the recruitment of specific CLA assemblies through opto/chemogenetic manipulations prevents attentional set-shifting. In conclusion, we propose that the CLA controls the reorganization of mPFC ensembles to enable attentional set-shifting, emphasizing a potential role of the CLA-mPFC network in attentional dysfunctions.