Which pharmacologic fMRI (phMRI) results have increased the understanding of Tourette syndrome (TS) and other tic disorders?

Updated: May 30, 2019
  • Author: William C Robertson, Jr, MD; Chief Editor: Stephen L Nelson, Jr, MD, PhD, FAACPDM, FAAN, FAAP  more...
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The author and his colleagues have studied volunteers with chronic tic syndromes and control subjects by using a pharmacologic activation functional magnetic resonance imaging (pharmacologic fMRI, or phMRI) design. [44] This method attempts to map and quantify the brain's responsiveness to a dopamine challenge. Preliminary analyses were complicated by methodological difficulties inherent in the blood oxygenation level–dependent (BOLD) fMRI signal response over long periods (unpublished data). Additional analyses are under way.

A subset of these patients participated in a pharmacologic-cognitive interaction fMRI study. Subjects performed a working memory ("2-back") task or a response inhibition ("go/no-go") task before and again during infusion of levodopa (with carbidopa). Some but not all other studies of patients with TS have shown higher-than-normal commission errors on response inhibition tasks. [45, 46, 47] However, in this study, no differences between groups were observed with the response inhibition task. [48]

As task performance was similar in the 2 groups, the results are best explained by a true difference in brain response between the 2 groups: The TS group apparently requires more activation of several working memory–related regions to sustain normal task performance. These exciting results, if confirmed, suggest that TS patients may have a dopamine-responsive abnormality of brain function in nonmotor as well as motor brain circuits.


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