title: Neural substrates of impaired sensorimotor timing in adult attention-deficit/hyperactivity disorder.
abstract: BACKGROUND
  Timing abilities are critical to the successful management of everyday activities and personal safety, and timing abnormalities have been argued to be fundamental to impulsiveness, a core symptom of attention-deficit/hyperactivity disorder (ADHD). Despite substantial evidence of timing deficits in ADHD youth, only two studies have explicitly examined timing in ADHD adults and only at the suprasecond time scale. Also, the neural substrates of these deficits are largely unknown for both youth and adults with ADHD. The present study examined subsecond sensorimotor timing and its neural substrates in ADHD adults.
  
  
  METHODS
  Using functional magnetic resonance imaging, we examined paced and unpaced finger tapping in a sample of 20 unmedicated adults with ADHD and 19 control subjects comparable on age, sex, and estimated IQ. The blood oxygenation level-dependent contrast response was used to estimate task-related neural activity.
  
  
  RESULTS
  Behavioral data showed no between-group differences in mean tapping rates but greater within-subject variability in tap-to-tap intervals for ADHD adults relative to control subjects. Importantly, ADHD adults had greater clock rather than motor variability, consistent with a central timing locus for the atypical movements. The imaging results demonstrated that, relative to control subjects, ADHD adults showed less activity in a number of regions associated with sensorimotor timing, including prefrontal and precentral gyri, basal ganglia, cerebellum, inferior parietal lobule, superior temporal gyri, and insula.
  
  
  CONCLUSIONS
  Our findings show that subsecond timing abnormalities in ADHD youth persist into adulthood and suggest that abnormalities in the temporal structure of behavior observed in ADHD adults result from atypical function of corticocerebellar and corticostriatal timing systems.
authors.affiliation: Clinical and Research Programs in Pediatric Psychopharmacology and Adult Attention Deficit Hyperactivity Disorder, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts, USA.
authors.forename: Eve M
authors.initials: EM
authors.lastname: Valera
authors.forename: Rebecca M C
authors.initials: RM
authors.lastname: Spencer
authors.forename: Thomas A
authors.initials: TA
authors.lastname: Zeffiro
authors.forename: Nikos
authors.initials: N
authors.lastname: Makris
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Spencer
authors.forename: Stephen V
authors.initials: SV
authors.lastname: Faraone
authors.forename: Joseph
authors.initials: J
authors.lastname: Biederman
authors.forename: Larry J
authors.initials: LJ
authors.lastname: Seidman
mesh_terms: D000328:Adult; D001289:Attention Deficit Disorder with Hyperactivity / Q000503:physiopathology*; D001479:Basal Ganglia / Q000502:physiology / Q000503:physiopathology; D001921:Brain / Q000502:physiology* / Q000503:physiopathology; D001931:Brain Mapping; D016022:Case-Control Studies; D002531:Cerebellum / Q000502:physiology / Q000503:physiopathology; D005260:Female; D005625:Frontal Lobe / Q000502:physiology / Q000503:physiopathology; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D011597:Psychomotor Performance / Q000502:physiology*; D012016:Reference Values; D013998:Time Perception / Q000502:physiology*; D055815:Young Adult