A Scaled Subprofile Statistical Model (SSM) of regional metabolic covariation was employed to identify functional brain networks in 10 Tourette syndrome (TS) patients (mean age, 41 years), with 10 normal volunteers as controls, in a study at North Shore University Hospital, Manhasset, New York. Quantitative fluorodeoxyglucose (FDG) and PET were used to calculate global and regional rates of glucose metabolism. While global glucose metabolic rates were normal in TS patients, SSM analysis identified bilateral metabolic increases in lateral premotor and supplementary motor cortex and midbrain, and decreases in caudate and thalamic metabolism. TS patients have a nonspecific pattern of increased motor cortical activity common to other hyperkinetic disorders, and a specific brain network involving reduced activity of limbic basal ganglia-thalamocortical projections. 
COMMENT. Two independent brain networks are identified in patients with Tourette syndrome: 1) increased metabolic activity of motor cortical regions involved in execution of movement; and 2) decreased metabolic activity in basal ganglia-thalamic areas governing TS global scale severity.