Functional and anatomical relationships among the amygdala, basal forebrain, ventral striatum, and cortex. An integrative discussion.

Two recent papers have questioned the concept of the amygdala as a functional and anatomically separate entity. Swanson and Petrovich go so far as to state that "the amygdala is neither a structural nor a functional unit." This novel concept is derived from the fact that the amygdala is a structure whose anatomical connections and neurochemical features are more strongly interrelated to adjacent parts of the temporal lobe and basal forebrain than to unique characteristics of its own. This is an emerging hypothetical concept of the "amygdala" that seems to repeat itself in many parts of this volume and merits further examination in the future. The basal forebrain and cortical circuitry described here seem to be critical for a set of behaviors/processes that could be collectively described as cognitive-emotive. For example, this would include arousal, attention, sensory processing, reinforcement, and finally associative learning, decision making, and memory. Collectively this circuitry influences the emotional, motivational, and cognitive state of an organism. More and more studies are demonstrating that small and localized manipulations of the brain can result in equally subtle and specific deficits that are associated with definable parts of the anatomical circuitry, neurotransmitters, and receptors of basal forebrain structures. These studies have been guided and influenced by the refined neuroanatomical and neurochemical investigations of Lennart Heimer and his colleagues. Interpretations of these studies are beginning to uncover distinct deficits that suggest explanations and potential treatments for many psychiatric and pathological degenerative disorders.