IS THE CAUDOMEDIAL SHELL OF THE NUCLEUS-ACCUMBENS PART OF THE EXTENDED AMYGDALA - A CONSIDERATION OF CONNECTIONS

The conceptual origins of two forebrain functional-anatomical systems, the ventral striatopallidum and extended amygdala, are reviewed brief ly, and reductionist and constructionist doctrines pertaining to descr iptions of forebrain organization are generally discussed briefly. The cortical, subcortical, and intrinsic connectional relationships of th e caudomedial shell of the nucleus accumbens, an anomalous component o f the ventral striatopallidum, are compared with those of the extended amygdala, leading to an attempt to formulate an assessment as to the extent to which the caudomedial shell might actually be regarded as a part of extended amygdala, or a transitional structure with a capacity to bridge extended amygdaloid and striatal mechanisms. The relatively distinct intrinsic circuitries and different outputs of the two are n oted. Extended amygdala projects most strongly to the posterior half o f the lateral hypothalamus and brainstem autonomic effector sites. Cau domedial shell and ventromedial ventral pallidum project throughout th e lateral preoptico-lateral hypothalamic continuum and are major compo nents in a basal ganglia-thalamocortical pathway to the prefrontal cor tex. It is concluded that connectional features distinguishing the cau domedial shell/ventromedial ventral pallidum and extended amygdala are of sufficient magnitude that the two should most usefully be regarded as separate, interacting functional-anatomical entities.