Frank A. Middleton

Chapter 32 Dentate output channels: motor and cognitive components

Publisher Summary This chapter reviews the basis for using selected strains of herpes simplex virus type 1 (HSV1) as transneuronal tracers to map circuits in the central nervous system (CNS) and presents some anatomical results on the organization of cerebellar projections via the thalamus to the frontal lobe. The results suggest that the cerebellum projects not only to the primary motor cortex but also to areas of the premotor, oculomotor, and prefrontal cortices. Furthermore, the projections to different cortical areas appear to originate from different regions of the cerebellar output nuclei. These findings help propose a new scheme of organization for cerebellar output—namely, the deep cerebellar nuclei; the dentate nucleus specifically contain multiple output channels, each of which projects to a distinct cortical area. The chapter presents some of the physiological observations indicating that individual output channels are concerned with different aspects of motor and/or cognitive behavior. The anatomical and physiological results reveal important features of the basic structural framework, which connects cerebellar output with the cerebral cortex.

The cerebellum: an overview

Abstract Life has been compared to a beautiful tapestry, woven in intricate design of many threads and colors. By means of physics, chemistry, physiology, anatomy, embryology and genetics we unravel this texture, separate its constituent threads and colors, but lose the pattern as a whole. These analytical sciences have enormously increased our knowledge of lifes constituent elements and processes, but the pattern of the tapestry is usually neglected or ignored. E.G. Conklin (1944) (p. 125 in Ref. [1]).

Fundamental and Clinical Evidence for Basal Ganglia Influences on Cognition

Over the past century, the term “basal ganglia” has at one time or another been used to indicate a wide variety of brain structures. In its present and most restrictive use, however, the term is generally reserved for three groups of brain structures called the “striatum,” “pallidum,” and “substantia nigra,” and an additional structure termed the “subthalamic nucleus” (STN). Table 1 outlines the basic subdivisions of the basal ganglia. The striatum can be separated into two general components, the dorsal striatum, which consists of the caudate and putamen, and the ventral striatum, which consists of the nucleus accumbens, septum, and olfactory tubercle. The nucleus accumbens, in turn, is subdivided into a lateral core region and medial shell region. In a similar manner, the pallidum can also be divided into multiple divisions, including a lateral or external segment of the globus pallidus (GPe), a medial or internal segment of the globus pallidus (GPi), and a portion that lies ventral and anterior to the anterior commissure, designated the ventral pallidum (VP). The GPi is further divided anatomically by a distinct fiber bundle into a lateral outer portion and a medial inner portion. Finally, the substantia nigra is also composed of more than one component, a cell group rich in neuromelanin called the pars compacta (SNpc), which is responsible for the black appearance of the nucleus in gross specimens, and an unpigmented cell group known as the pars reticulata (SNpr). Further subdivision of the SNpr is also possible, due to the presence of a distinct subpopulation of cells located dorsolaterally in the SNpr, and is referred to as the pars lateralis.