Projections from the Temporal Cortex to the Basal Nucleus of the Amygdala in the Macaque

Ashley Bui, Sarah Friedman, Emily A. Kelly, and Julie L. Fudge

The amygdala is a complex brain structure involved in the emotional coding of complex sensory stimuli. In primates, including humans, visual information in the form of faces is one of the most important drivers of amygdala activity. We asked whether information from the temporal cortex – where visual information is hierarchically processed – shows a particular pattern of inputs to one of the main amygdala nuclei, the basal nucleus (BA). Following injections of neuronal tracers into the BA in four monkeys, we examined the temporal cortex for retrogradely labeled cells using immunocytochemistry and a neuron tracing software (Neurolucida). The most ventromedial injection in the BA had the most restricted distribution of labeled cells, found mainly in the entorhinal cortex. A slightly more dorsal injection resulted in additional dense labeling in the perirhinal cortex and moderate numbers of labeled cells in the inferotemporal cortex (TE). Increasingly dorsal injections resulted in heavy concentrations of labeled cells in the entorhinal and perirhinal cortices and TE, with additional labeled cells in the superior temporal gyrus (STG) and sulcus (STS). There is a topography of temporal cortical inputs to the BA with the most ventral regions receiving restricted inputs from entorhinal cortex. Inputs from perirhinal cortex, and eventually, TE, and STS/STG progressively contribute additional information to more dorsal BA sites. The entorhinal cortex plays a role in episodic memory, which is the memory of highly personal detailed information. The perirhinal cortex is intimately linked to the entorhinal cortex, and is implicated in visual place recognition. TE and adjacent STG and STS are more directly related to perception of ongoing visual information such as objects and faces. While memory-based information from entorhinal and perirhinal cortex, respectively, influence the entire BA, the dorsal regions are specialized in receiving inputs of faces and objects in the immediate environment.