PMID: 2094891Jan 1, 1990Paper

Basal ganglia-thalamocortical circuits: parallel substrates for motor, oculomotor, "prefrontal" and "limbic" functions

Progress in Brain Research
G E AlexanderM R Delong

Abstract

The central theme of the "segregated circuits" hypothesis is that structural convergence and functional integration occurs within, rather than between, each of the identified circuits. Admittedly, the anatomical evidence upon which this scheme is based remains incomplete. The hypothesis continues to be predicated largely on comparisons of anterograde and retrograde labeling studies carried out in different sets of animals. Only in the case of the "motor" circuit has evidence for the continuity of the loop been demonstrated directly in individual subjects; for the other circuits, such continuity is inferred from comparisons of data on different components of each circuit obtained in separate experiments. Because of the marked compression of pathways leading from cortex through basal ganglia to thalamus, comparisons of projection topography across experimental subjects may be hazardous. Definitive tests of the hypothesis of maintained segregation await additional double- and multiple-label tract-tracing experiments wherein the continuity of one circuit, or the segregation of adjacent circuits, can be examined directly in individual subjects. It is worthy of note, however, that the few studies to date that have employed this metho...Continue Reading

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