A PROPOSED CONCEPTUAL REORGANIZATION OF THE BASAL GANGLIA AND TELENCEPHALON
1980; Elsevier BV; Linguagem: Inglês
10.1016/b978-0-08-025501-9.50028-4
Autores Tópico(s)Functional Brain Connectivity Studies
ResumoA reordering of priorities applied to the criteria for grouping neuronal populations suggests a simpler conceptual organization of the basal ganglia and telencephalon than that currently in general use. The proposed scheme reduces the emphasis of the obvious geographical divisions imposed by the major white matter bundles and the cerebral ventricle, and emphasizes instead such criteria as a common internal histology, similar input-output patterns and characteristic neurotransmitters. By these reordered criteria, almost the entire telencephalon can be subdivided into three concentric tiers. The outermost tier (tier I) encompasses the structures derived embryologically from the pallium, the neocortex and the allocortex. The second tier (tier II) includes the caudate nucleus, the putamen, the nucleus accumbens septi and parts of the olfactory tubercle. The third tier (tier III) is composed of the external pallidal segment, the internal pallidal segment, the nondopaminergic part of the substantia nigra, and perhaps also parts of the substantial innominata. It is suggested that while many characteristics of the telencephalon and basal ganglia lend themselves to subdivision into 'sensory—, 'motor—, 'associational' and 'limbic' sectors, at least some features of organization appear to transgress such distinctions. The proposed reorganization does not deny the existence of such classical functional and anatomical subdivisions but focuses attention instead on two distinct telencephalic outflow systems each of which appears to serve overlapping and widespread parts of the telecephalon. One outflow system leaves the structures in tier I to influence monosynaptically the diencephalon, mesencephalon, pons, medulla or even the spinal cord, while the other outflow system follows a polysynaptic route with at least two intermediate synapses, the first between the tier I and tier II neurons and a second between the tier II and tier III neurons. Some implications of this perspective perhaps useful to the physiologist, pathologist and clinician are discussed.
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