Classic neuropsychologic methods combined with newer cognitive neuroscience concepts and contemporary neuroimaging technologies provide the most powerful means for probing human brain structure and function in vivo. In the first three articles of this issue, the anatomy and neurochemistry of the basal ganglia are reviewed. In this article, the functions of the basal ganglia are explored, specifically focusing on the role of the striatum across cognitive, sensorimotor, and affective/motivational domains. By emphasizing the relationship between brain and behavior as well as contemporary methods of neuroimaging and neuropsychology, this article is intended to serve as a bridge between basic science and clinical applications.

In addition to a discussion of the normal functioning of these systems, four neuropsychiatric disorders are presented as examples to illustrate the utility of neuroimaging and neuropsychology in medicine. Obsessive–compulsive disorder (OCD) is characterized by intrusive cognitions, repetitive behaviors, and accompaniments of anxiety<sup>5 American Psychiatric Association Diagnostic and Statistical Manual of Mental Disorders DC, Washington: American Psychiatric Association (1994). 

Cliquez ici pour aller à la section Références</sup>; although the causes and neuropathology of OCD are unknown, corticostriatal circuits involving the caudate nucleus have been implicated (see articles 9 and 10 in this issue). Tourette syndrome (TS) is a disorder of involuntary movements and vocalizations, characterized by intrusive premonitory sensations and “urges”<sup>5 American Psychiatric Association Diagnostic and Statistical Manual of Mental Disorders DC, Washington: American Psychiatric Association (1994). 

Cliquez ici pour aller à la section Références, 96 Leckman J.F., Walker D.E., Cohen D.J. Premonitory urges in Tourette's syndrome Am J Psychiatry 1993 ;  150 : 98

Cliquez ici pour aller à la section Références</sup> (see article elsewhere in this issue). Although a diathesis for TS appears to be heritable and related to one subtype of OCD,<sup>126 Pauls D.L., Alsobrook J.P., Goodman W. , et al. A family study of obsessive-compulsive disorder Am J Psychiatry 1995 ;  152 : 76

Cliquez ici pour aller à la section Références</sup> the pathology and causes of TS likewise remain poorly understood. Complementing OCD, corticostriatal circuits involving sensorimotor cortex and the putamen have been implicated in TS. Huntington's disease (HD) provides a stark contrast to other basal ganglia disorders in that its genetic cause and its neuropathology are well established (see article elsewhere in this issue). HD is a degenerative disorder, involving cell loss that most prominently affects the neostriatum, resulting in choreiform movements, as well as cognitive and behavioral manifestations. Finally, Parkinson's disease (PD) represents one of a variety of conditions presenting with characteristic motor signs including akinesia, rigidity, and tremor (see article elsewhere in this issue). Like HD, PD is a degenerative disorder with well-established neuropathologic changes within the basal ganglia that can lead to cognitive and behavioral abnormalities beyond its heralded motor manifestations. In contrast to HD, however, the cause of PD is unknown, and the primary neuropathologic changes occur within the substantia nigra, affecting projections to the striatum rather than striatal neurons per se. The various uses and implications of neuroimaging and neuropsychology across these exemplary disorders mirror the assortment of causes, neuropathologies, pathophysiologies, and clinical challenges that basal ganglia diseases present.