title: Abnormal neural reactivity to unpredictable sensory events in attention-deficit/hyperactivity disorder.
abstract: BACKGROUND
  Cortical oscillations in the sensorimotor region in the 8-12-Hz range ("mu rhythms") are associated with basic somatosensory and motor processes as well as top-down processes such as learning, attention, expectancy, and inhibition. Recent studies suggest that reactivity of these rhythms to sensory input reflects a link between perception and action and that abnormalities in this reactivity might reflect impairment in perception-to-action mechanisms. Individuals with attention-deficit/hyperactivity disorder (ADHD) are impaired in tasks requiring sensorimotor function, attention, expectancy, and inhibition, yet their sensorimotor mu responses are unknown. Thus, we investigated mu reactivity in a group of adults with ADHD.
  
  
  METHODS
  Sixteen adults with ADHD and 16 matched control subjects received median nerve stimulation in predictable patterns (trains of four stimuli followed by 4-sec gap) or unpredictable patterns (randomly presented trains of two, four, or six stimuli followed by 4-sec gap). With magnetoencephalography, we examined the effects of stimulus patterning (predictable, unpredictable) on mu reactivity to somatosensory stimuli.
  
  
  RESULTS
  Compared with control subjects, the ADHD group showed lower mu reactivity overall and no modulation by unpredictable somatosensory input. By contrast, the control group showed robust mu reactivity to stimuli presented in unpredictable but not predictable patterns. These changes were stronger in the contralateral hemisphere compared with the ADHD group.
  
  
  CONCLUSIONS
  Cortical mu rhythms are modulated by stimulus predictability and might be involved in attentional alerting (awareness of when an unexpected stimulus occurs). Diminished mu modulation in adult ADHD suggests a possible underlying deficit in the perception-to-action system.
authors.affiliation: Neurosciences and Mental Health Program, the Hospital for Sick Children, Toronto, Ontario, Canada.
authors.forename: Colleen
authors.initials: C
authors.lastname: Dockstader
authors.forename: William
authors.initials: W
authors.lastname: Gaetz
authors.forename: Douglas
authors.initials: D
authors.lastname: Cheyne
authors.forename: Rosemary
authors.initials: R
authors.lastname: Tannock
mesh_terms: D000328:Adult; D001289:Attention Deficit Disorder with Hyperactivity / Q000503:physiopathology*; D016022:Case-Control Studies; D005073:Evoked Potentials, Somatosensory / Q000502:physiology*; D005260:Female; D007839:Functional Laterality / Q000502:physiology; D006801:Humans; D015225:Magnetoencephalography / Q000523:psychology; D008297:Male; D008475:Median Nerve / Q000502:physiology; D012727:Sex Characteristics; D013003:Somatosensory Cortex / Q000503:physiopathology