title: Limbic and motor circuits involved in symmetry behavior in Tourette's syndrome.
abstract: OBJECTIVE
  The need for symmetry and ordering objects related to a "just right"-feeling is a common symptom in Tourette's syndrome (TS) and resembles symmetry behavior in obsessive-compulsive disorder, but its pathophysiology is unknown. We used a symptom provocation paradigm to investigate the neural correlates of symmetry behavior in TS and hypothesized the involvement of frontal-striatal and limbic brain areas.
  
  
  METHODS
  Pictures of asymmetrically and symmetrically arranged objects were presented in randomized blocks (4 blocks of each condition) to 14 patients with TS and 10 matched healthy controls (HC). A H2                  15O positron emission tomography scan was acquired during each stimulus block, resulting in 8 scans per subject. After each scan, state anxiety and symmetry behavior (the urge to rearrange objects) were measured using a visual analogue scale.
  
  
  RESULTS
  During the asymmetry condition, TS patients showed increased regional cerebral blood flow (rCBF) in the anterior cingulate cortex, supplementary motor area, and inferior frontal cortex, whereas HC showed increased rCBF in the visual cortex, primary motor cortex, and dorsal prefrontal cortex. Symmetry ratings during provocation correlated positively with orbitofrontal activation in the TS group and sensorimotor activation in the HC group, and negatively with dorsal prefrontal activity in HC.
  
  
  CONCLUSIONS
  Results suggest that both motor and limbic circuits are involved in symmetry behavior in TS. Motor activity may relate to an urge to move or perform tics, and limbic activation may indicate that asymmetry stimuli are salient for TS patients. In contrast, symmetry provocation in HC resulted in activation of brain regions implicated in sensorimotor function and cognitive control.
authors.affiliation: Department of Psychiatry, VU University Medical Center, Amsterdam, the Netherlands. fe.devries@vumc.nl
authors.forename: Froukje E
authors.initials: FE
authors.lastname: de Vries
authors.forename: Odile A
authors.initials: OA
authors.lastname: van den Heuvel
authors.forename: Danielle C
authors.initials: DC
authors.lastname: Cath
authors.forename: Henk J
authors.initials: HJ
authors.lastname: Groenewegen
authors.forename: Anton J L M
authors.initials: AJ
authors.lastname: van Balkom
authors.forename: Ronald
authors.initials: R
authors.lastname: Boellaard
authors.forename: Adriaan A
authors.initials: AA
authors.lastname: Lammertsma
authors.forename: Dick J
authors.initials: DJ
authors.lastname: Veltman
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D001931:Brain Mapping; D002540:Cerebral Cortex / Q000000981:diagnostic imaging; D002560:Cerebrovascular Circulation / Q000502:physiology*; D003342:Corpus Striatum / Q000000981:diagnostic imaging; D005260:Female; D007839:Functional Laterality / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009483:Neuropsychological Tests; D009770:Obsessive Behavior / Q000000981:diagnostic imaging / Q000209:etiology* / Q000473:pathology*; D010775:Photic Stimulation; D049268:Positron-Emission Tomography; D011569:Psychiatric Status Rating Scales; D013223:Statistics as Topic; D005879:Tourette Syndrome / Q000150:complications* / Q000000981:diagnostic imaging / Q000473:pathology