CORTICAL PATHWAYS TO THE MAMMALIAN AMYGDALA

The amygdaloid nuclear complex is critical for producing appropriate e motional and behavioral responses to biologically relevant sensory sti muli. It constitutes an essential link between sensory and limbic area s of the cerebral cortex and subcortical brain regions, such as the hy pothalamus, brainstem, and striatum, that are responsible for elicitin g emotional and motivational responses. This review summarizes the ana tomy and physiology of the cortical pathways to the amygdala in the ra t, cat and monkey. Although the basic anatomy of these systems in the cat and monkey was largely delineated in studies conducted during the 1970s and 1980s, detailed information regarding the cortico-amygdalar pathways in the rat was only obtained in the past several years. The p urpose of this review is to describe the results of recent studies in the rat and to compare the organization of cortico-amygdalar projectio ns in this species with that seen in the cat and monkey. In all three species visual, auditory, and somatosensory information is transmitted to the amygdala by a series of modality-specific cortico-cortical pat hways (''cascades'') that originate in the primary sensory cortices an d flow toward higher order association areas. The cortical areas in th e more distal portions of these cascades have stronger and more extens ive projections to the amygdala than the more proximal areas. In all t hree species olfactory and gustatory/visceral information has access t o the amygdala at an earlier stage of cortical processing than vis aud itory and somatosensory information. There are also important polysens ory cortical inputs to the mammalian amygdala from the prefrontal and hippocampal regions. Whereas the overall organization of cortical path ways is basically similar in all mammalian species, there is anatomica l evidence which suggests that there are important differences in the extent of convergence of cortical projections in the primate versus th e nonprimate amygdala. (C) 1998 Elsevier Science Ltd. All rights reser ved.