Over the last 4 years since the funding of this project, the UT Houston SAR-MDC has shown that cocaine dependence is associated with behavioral deficits including decision-making, behavioral inhibition, and the broader clinical construct of impulsivity. Likewise, we found differences between cocaine dependent subjects and non-drug using controls on Magnetic Resonance Imaging (MRI) measures of brain structure and function. In addition, we have acquired data showing that within cocaine users there is an association between these behavioral deficits and alterations in brain structure, brain function, and poor treatment response. For the renewal of this project, the focus will advance to determining the specific role of these brain MRI findings in treatment outcome by means of a carefully chosen battery of functional and structural MRI techniques in order to predict treatment response to specific classes of medication based on mechanism of action. Our previous blood oxygen level dependent (BOLD) fMRI data showed that cocaine dependent subjects (relative to controls) have (1) less dorsolateral prefrontal cortical, striatal, and thalamic activation during a working memory task, possibly reflecting impaired dopamine function;(2) greater activation in medial orbitofrontal cortex during impulsive responding on a Go-Nogo task, possibly reflecting impaired serotonin function;and (3) greater activation in medial orbitofrontal cortex and medial frontal cortex after negative feedback on a reversal learning task, also possibly reflecting impairment of serotonin function. In order to follow-up the treatment implications of this data, this project will examine (a) pretreatment brain activation on these tasks as predictors of neurotransmitter-specific treatment response, and (b) eariy changes (after three weeks of pharmacotherapy) in task-related fMRI activation as predictors of subsequent longer-term neurotransmitter-specific treatment response. In addition, the relationship between treatment response and measures of white-matter structural integrity as measured by diffusion tensor MRI (DTI) and magnetization transfer ratio MRI (MTR) will be examined.
In spite of the significant public health concerns regarding cocaine dependence, there is as yet no FDA approved medication for the disorder. If a greater understanding of the basic neurobiology of the effects of chronic cocaine use on the human brain can be gained from this study it would be significant and could lead to the development of new medications for cocaine dependence.
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