Loss of functional specificity in the dorsal striatum of chronic cocaine users

Background: Although research into the effects of cocaine has focused on the ventral striatum, recent reports have identified a significant role for the dorsal striatum. Given the importance of the dorsal striatum in motor control, the purpose of the present study was to investigate potential sensorimotor deficits among cocaine users and the functional basis of these deficits within the striatum. Methods: Functional magnetic resonance imaging data were collected from 14 right-handed, non-treatment seeking chronic cocaine users and 14 age and gender matched controls during performance of two finger-sequencing paradigms that differentially activate the caudate (internally-guided) and the putamen (externally-guided) interleaved with blocks of rest. The total percent signal change in the dorsal striatum and the contribution of the left and right caudate and putamen were calculated and compared across groups and tasks. Results: Significant deficits in sensorimotor control were observed in cocaine users for both motor tasks, with the most severe impairments present during internally-guided movements. Cocaine users lacked the typical functional segregation observed in the dorsal striatum of the control subjects. The total percent signal change in the dorsal striatum was not significantly different between the groups, but cocaine users activated significantly less contralateral caudate and putamen for internally-guided versus externally-guided movements, respectively. Conclusion: These data provide clear evidence that chronic cocaine users have significant motor performance deficits that are accompanied by disrupted processing within the dorsal striatum. These data suggest the effects of cocaine extend beyond the confines of the motivational domains of the ventral striatum.