SUBSTANTIA INNOMINATA - A NOTION WHICH IMPEDES CLINICAL-ANATOMICAL CORRELATIONS IN NEUROPSYCHIATRIC DISORDERS

Comparative neuroanatomical investigations in primates and non-primate s have helped disentangle the anatomy of the basal forebrain region kn own as the substantia innominata. The most striking aspect of this reg ion is its subdivision into two major parts. This reflects the fundame ntal organizational scheme for this portion of the forebrain. Accordin g to this scheme, two major subcortical telencephalic structures, i.e. the striatopallidal complex and extended amygdala, form large diagona lly oriented bands. The rostroventral extension of the pallidum accoun ts for a large part of the rostral subcommissural substantia innominat a, while the sublenticular substantia innominata is primarily occupied by elements of the extended amygdala. Also dispersed across this regi on is the basal nucleus of Meynert, which is part of a more or less co ntinuous collection of cholinergic and non-cholinergic corticopetal an d thalamopetal cells, which stretches from the septum-diagonal band ro strally to the caudal globus pallidus. The basal nucleus of Meynert is especially prominent in the primate, where it is sometimes inappropri ately applied as a synonym for the substantia innominata, thereby taci tly ignoring the remaining components. In most mammals, the extended a mygdala presents itself as a ring of neurons encircling the internal c apsule and basal ganglia. The extended amygdala may be further subdivi ded, i.e. into the central extended amygdala (related to the central a mygdaloid nucleus) and the medial extended amygdala (related to the me dial amygdaloid nucleus), which generally form separate corridors both in the sublenticular region and along the supracapsular course of the stria terminalis. The extended amygdala is directly continuous with t he caudomedial shell of the accumbens, and to some extent appears to m erge with it. Together the accumbens shell and extended amygdala form an extensive forebrain continuum, which establishes specific neuronal circuits with the medial prefrontal-orbitofrontal cortex and medial te mporal lobe. This continuum is particularly characterized by a promine nt system of long intrinsic association fibers, and a variety of highl y differentiated downstream projections to the hypothalamus and brains tem. The various components of the extended amygdala, together with th e shelf of the accumbens, are ideally structured to generate endocrine , autonomic and somatomotor aspects of emotional and motivational stat es. Behavioral observations support this proposition and demonstrate t he relevance of these structures to a variety of functions, ranging fr om the various elements of the reproductive cycle to drug-seeking beha vior. The neurochemical and connectional Features common to the accumb ens shell and the extended amygdala are especially relevant to underst anding the etiology and treatment of neuropsychiatric disorders. This is discussed in general terms, and also in specific relation to the ne urodevelopmental theory of schizophrenia and to the neurosurgical trea tment of neuropsychiatric disorders.