Cocaine administration decreases functional connectivity in human primary visual and motor cortex as detected by functional MRI

Functional magnetic resonance imaging (fMRI) was conducted to observe the effects of cocaine administration on the physiological fluctuations of fMRI signal in two brain regions. Seven long-term cocaine users with an average age of 32 years and 8 years of cocaine use history were recruited for the study. A T₂/(*)-weighted fast echo-planar imaging (EPI) pulse sequence was employed at 1.5 T to acquire three sets of brain images for each subject under three conditions (at rest, after saline injection, and after cocaine injection [0.57 mg/kg]). Cross- correlation maps were constructed using the synchronous, low frequency signal from voxel time courses after filtering respiratory, cardiac, and other physiological noise. A quantitative evaluation of the changes in functional connectivity was made using spatial correlation coefficient (SCC) analysis. A marked 50% reduction in SCC values in the region of primary visual cortex and 43% reduction in SCC values in the region of primary motor cortex were observed after cocaine administration. This significant reduction in SCC values in these cortical regions is a reflection of changes in neuronal activity. It is suggested that the observed changes in low frequency components after acute cocaine administration during a resting, no-task situation may be used as a baseline reference source when assessing the effects of cocaine on task-driven activation or on mesolimbic dopamine pathways.