Topographic organisation of the claustrum-amygdala-prefrontal circuitry in the common marmoset (Callithrix jacchus).

Recent rodent studies suggest that the claustrum complex, an evolutionarily conserved structure with widespread cortical connectivity, plays a role in modulation of anxiety-like behaviour via projections to the basolateral amygdala. However, this circuitry remains poorly defined in primates. Here, we investigated structural connectivity between the claustrum complex, amygdala, and prefrontal cortex in the adult common marmoset (Callithrix jacchus) using diffusion-weighted tractography and neuroanatomical tracing. Tracer injections were performed under anaesthesia via stereotaxic surgery. One marmoset received a biotinylated dextran amine injection into the basolateral amygdala, while four others received fluorescent retrograde tracers targeting the frontopolar cortex, orbitofrontal cortex, medial prefrontal cortex, and somatosensory cortex. Brains were processed for histology and tracer visualization. Diffusion weighted imaging and MRI tractography was performed on publicly available data from 24 marmosets from the Marmoset Brain Mapping Project (MBMv4; Tian et al. 2022; www.marmosetbrainmapping.org). The dorsal endopiriform nucleus was the region of the claustrum complex with the highest structural connectivity with both the amygdala and prefrontal cortex, showing particularly strong connectivity with the lateral amygdala and posterior orbitofrontal cortex, and more moderate connectivity with the medial prefrontal cortex. Our findings demonstrate a distinct claustro-amygdalo-prefrontal subcircuit in the marmoset, providing structural foundation for future studies examining the functional relevance of this circuitry in the primate brain.