Subcortical projections from the amygdaloid complex.

It has long been known that the amygdala has substantial subcortical projections to the bed nucleus of the stria terminalis, the hypothalamus and the mediodorsal nucleus of the thalamus (e.g., Nauta, 1961; Cowan et al., 1965; Heimer and Nauta, 1969; De Olmos, 1972). Partially because of this, the function of the amygdaloid complex has been thought to be primarily related to visceral and autonomic mechanisms (e.g., Kaada, 1972). This concept has been somewhat altered by more recent studies. It is now clear that there are also widespread amygdaloid projections to the cerebral cortex (see Amaral, this volume), and that the complex is involved in cognitive as well as visceral functions (e.g., Gloor et al., 1982). However, recent investigations have also emphasized the subcortical projections from the amygdaloid nuclei, and have shown that they are even more complex and extensive than were previously thought. For example, the central amygdaloid nucleus projects not only to the lateral hypothalamus, but also to the full extent of the brainstem and even into the spinal cord (e.g., Hopkins, 1975; Price and Amaral, 1981; Mizuno et al., 1985). At the other end of the neuraxis, the amygdaloid nuclei provide the major telencephalic input to the nucleus basalis and other cell groups in the basal forebrain (Russchen et al., 1985b).