Brainwide mesoscale functional networks revealed by focal infrared neural stimulation of the amygdala.

The primate amygdala serves to evaluate emotional content of sensory inputs and modulate emotional and social behaviors; prefrontal, multisensory and autonomic aspects of these circuits are mediated predominantly via the basal (BA), lateral (LA), and central (CeA) nuclei, respectively. Based on recent electrophysiological evidence suggesting mesoscale (millimeters-scale) nature of intra-amygdala functional organization, we have investigated the connectivity of these nuclei using infrared neural stimulation (INS) of single mesoscale sites coupled with mapping in ultrahigh field 7T functional magnetic resonance imaging (fMRI), namely INS-fMRI. Following stimulation of multiple sites within amygdala of single individuals, a 'mesoscale functional connectome' of amygdala connectivity (of BA, LA, and CeA) was obtained. This revealed the mesoscale nature of connected sites, the spatial patterns of functional connectivity, and the topographic relationships (parallel, sequential, or interdigitating) of nucleus-specific connections. These findings provide novel perspectives on the brainwide circuits modulated by the amygdala.