title: Button-pressing affects P300 amplitude and scalp topography.
abstract: BACKGROUND
  Scant and equivocal research exists examining the effects of button-pressing on P300. Button-pressing may decrease P300 latency and amplitude. The melding of motor potentials and P300 may also confound studies of P300 topography, such as studies of temporal scalp-area asymmetries in schizophrenia.
  
  
  METHODS
  P300 was measured on button-press and silent-count tasks in control subjects. An estimate of motor activity was constructed from a simple reaction time task, with reaction times matched to the button-press task. The motor estimate was subtracted from the button-press P300 to assess Kok's (1988) additive model. Lastly, lateral P300 from schizophrenia patients was compared with each condition's P300.
  
  
  RESULTS
  P300 was smaller and its topography different in the button-pressing task relative to silent-counting. The motor-correction procedure generated a P300 with normal topography. Comparison of the button-press P300 in controls to the silent-count P300 in schizophrenia patients reduced a significant lateral asymmetry to trend level. This asymmetry was significant after the correction procedure.
  
  
  CONCLUSIONS
  Button-pressing generates smaller P300 than silent-counting. Also, P300 topography in button-pressing tasks is confounded by motor potentials. The distortion can be corrected with a motor potential estimate. Motor potentials can occlude differences in P300 topography between groups.
authors.affiliation: Department of Psychiatry, Cognitive Neuroscience Laboratory, McLean Hospital NBG-21, Harvard Medical School, 115 Mill Street, Belmont, MA 02178-9106, USA.
authors.forename: D F
authors.initials: DF
authors.lastname: Salisbury
authors.forename: B
authors.initials: B
authors.lastname: Rutherford
authors.forename: M E
authors.initials: ME
authors.lastname: Shenton
authors.forename: R W
authors.initials: RW
authors.lastname: McCarley
mesh_terms: D000328:Adult; D001921:Brain / Q000502:physiology*; D001931:Brain Mapping; D004292:Dominance, Cerebral; D018913:Event-Related Potentials, P300 / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008433:Mathematics; D008606:Mental Processes / Q000502:physiology; D008875:Middle Aged; D009068:Movement / Q000502:physiology*; D011930:Reaction Time / Q000502:physiology; D012535:Scalp / Q000502:physiology; D012559:Schizophrenia / Q000503:physiopathology; D012565:Schizophrenic Psychology