Unimodal Responses Prevail within the Multisensory Claustrum

The claustrum receives afferent inputs from multiple sensory-related brain areas, prompting speculation about a role in integrating information across sensory modalities. Here we directly test this hypothesis by probing neurons in the primate claustrum for functional characteristics of multisensory processing. To this end we recorded neuronal responses to naturalistic audio-visual stimuli from the claustra of alert monkeys. Our results reveal the existence of distinct claustral zones comprised of unimodal neurons associated with the auditory and visual modalities. In a visual zone within the ventral claustrum neurons responded to visual stimuli but not to sounds, whereas in an auditory zone located within the central claustrum neurons responded to sounds but not to visual stimuli. Importantly, we find that neurons within either zone are not influenced by stimuli in the other modality and do not exhibit the typical response characteristics usually associated with multisensory processing. While these results confirm the notion of the claustrum as a multisensory structure per se, they argue against the hypothesis of the claustrum serving as an integrator of sensory information.