title: Cluster analysis of behavioural and event-related potentials during a contingent negative variation paradigm in remitting-relapsing and benign forms of multiple sclerosis.
abstract: BACKGROUND
  Event-related potentials (ERPs) may be used as a highly sensitive way of detecting subtle degrees of cognitive dysfunction. On the other hand, impairment of cognitive skills is increasingly recognised as a hallmark of patients suffering from multiple sclerosis (MS). We sought to determine the psychophysiological pattern of information processing among MS patients with the relapsing-remitting form of the disease and low physical disability considered as two subtypes: 'typical relapsing-remitting' (RRMS) and 'benign MS' (BMS). Furthermore, we subjected our data to a cluster analysis to determine whether MS patients and healthy controls could be differentiated in terms of their psychophysiological profile.
  
  
  METHODS
  We investigated MS patients with RRMS and BMS subtypes using event-related potentials (ERPs) acquired in the context of a Posner visual-spatial cueing paradigm. Specifically, our study aimed to assess ERP brain activity in response preparation (contingent negative variation -CNV) and stimuli processing in MS patients. Latency and amplitude of different ERP components (P1, eN1, N1, P2, N2, P3 and late negativity -LN) as well as behavioural responses (reaction time -RT; correct responses -CRs; and number of errors) were analyzed and then subjected to cluster analysis.
  
  
  RESULTS
  Both MS groups showed delayed behavioural responses and enhanced latency for long-latency ERP components (P2, N2, P3) as well as relatively preserved ERP amplitude, but BMS patients obtained more important performance deficits (lower CRs and higher RTs) and abnormalities related to the latency (N1, P3) and amplitude of ERPs (eCNV, eN1, LN). However, RRMS patients also demonstrated abnormally high amplitudes related to the preparation performance period of CNV (cCNV) and post-processing phase (LN). Cluster analyses revealed that RRMS patients appear to make up a relatively homogeneous group with moderate deficits mainly related to ERP latencies, whereas BMS patients appear to make up a rather more heterogeneous group with more severe information processing and attentional deficits.
  
  
  CONCLUSIONS
  Our findings are suggestive of a slowing of information processing for MS patients that may be a consequence of demyelination and axonal degeneration, which also seems to occur in MS patients that show little or no progression in the physical severity of the disease over time.
authors.affiliation: Department of Experimental Psychology, University of Seville, Seville, Spain. javgonros@us.es
authors.forename: Javier J
authors.initials: JJ
authors.lastname: Gonzalez-Rosa
authors.forename: Manuel
authors.initials: M
authors.lastname: Vazquez-Marrufo
authors.forename: Encarnacion
authors.initials: E
authors.lastname: Vaquero
authors.forename: Pablo
authors.initials: P
authors.lastname: Duque
authors.forename: Monica
authors.initials: M
authors.lastname: Borges
authors.forename: Carlos M
authors.initials: CM
authors.lastname: Gomez-Gonzalez
authors.forename: Guillermo
authors.initials: G
authors.lastname: Izquierdo
mesh_terms: D000328:Adult; D000368:Aged; D016000:Cluster Analysis; D003265:Contingent Negative Variation / Q000502:physiology*; D003463:Cues; D004185:Disability Evaluation; D004569:Electroencephalography; D005071:Evoked Potentials / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009103:Multiple Sclerosis / Q000175:diagnosis* / Q000503:physiopathology*; D010775:Photic Stimulation / Q000379:methods; D011601:Psychophysics; D011930:Reaction Time; D012008:Recurrence; D013028:Space Perception / Q000502:physiology; D013223:Statistics as Topic