title: Distinct modulation of event-related potentials during motor preparation in patients with motor conversion disorder.
abstract: OBJECTIVE
  Conversion paresis patients and healthy people feigning weakness both exhibit weak voluntary movement without detectable neuropathology. Uniquely, conversion patients lack a sense of conscious awareness of the origin of their impairment. We investigated whether conversion paresis patients show distinct electroencephalographic (EEG) markers associated with their unconscious movement deficits.
  
  
  METHODS
  Six unilateral upper limb conversion paresis patients, 12 feigning participants asked to mimic weakness and 12 control participants performed a precued reaction time task, requiring movements of either hand, depending on precue information. Performance measures (force, reaction and movement time), and event-related EEG potentials (ERP) were compared, between groups and across hands or hemisphere, using linear mixed models.
  
  
  RESULTS
  Feigners generated the same inter-hand difference in reaction and movement time as expressed by patients, even though no specific targets were set nor feedback given on these measures. We found novel ERP signatures specific to patients. When the symptomatic hand was precued, the P3 ERP component accompanying the precue was dramatically larger in patients than in feigning participants. Additionally, in patients the earlier N1 ERP component was diminished when the precue signalled either the symptomatic or asymptomatic hand.
  
  
  CONCLUSIONS
  These results are consistent with previous suggestions that lack of awareness of the origin of their symptoms in conversion disorder patients may result from suppression of brain activity normally related to self-agency. In patients the diminished N1 to all precues is consistent with a generalised reduction in cognitive processing of movement-related precues. The P3 enhancement in patients is unlikely to simply reflect changes required for generation of impaired movements, because it was not seen in feigners showing the same behavioural deficits. Rather, this P3 enhancement in patients may represent a neural biomarker of unconscious processes, including additional emotional loading, related to active suppression of brain circuits involved in the attribution of self-agency.
authors.affiliation: School of Physical Education, University of Otago, Dunedin, New Zealand. rebekah.blakemore@otago.ac.nz
authors.forename: Rebekah L
authors.initials: RL
authors.lastname: Blakemore
authors.forename: Brian I
authors.initials: BI
authors.lastname: Hyland
authors.forename: Graeme D
authors.initials: GD
authors.lastname: Hammond-Tooke
authors.forename: J Greg
authors.initials: JG
authors.lastname: Anson
mesh_terms: D000368:Aged; D003291:Conversion Disorder / Q000503:physiopathology*; D004569:Electroencephalography; D004585:Electrooculography; D005071:Evoked Potentials; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009068:Movement; D011597:Psychomotor Performance