title: Cognitive processes in two-point discrimination: an ERP study.
abstract: OBJECTIVE
  To elucidate the temporal features of the cognitive process in two-point discrimination (TPD).
  
  
  METHODS
  We measured somatosensory event-related potentials (ERPs) in 9 subjects during the TPD task, in which we provided a pair of electrical pulses simultaneously, altering the distance between the electrodes. We analyzed the TPD-related ERPs and investigated the relationship between the potentials and the subjects' judgments.
  
  
  RESULTS
  During the TPD task, a negative potential approximately 140 ms after the stimulation (N140) was enhanced as compared to a stimulus counting task. Two late positive components, LPC-1 and LPC-2, whose peak latencies were 300 and 500 ms, respectively, were identified only in the TPD task. The LPC-1 was recorded dominantly in the fronto-central area, while the LPC-2 was detected dominantly in the centro-parietal area. The amplitude of the LPC-2 was significantly modulated by the degree of consistency in the subjects' judgment. On the other hand, these ERP components did not show significant difference between the alternate judgments, i.e. 'one-point' or 'two-point' judgment.
  
  
  CONCLUSIONS
  Our results suggest that the N140 is related to the attention toward the stimulation. The LPC-1 and LPC-2 are likely to correspond to the processes represented by P3a and P3b, based on their temporal and spatial behavior.
authors.affiliation: Department of Integrative Physiology, National Institute for Physiological Sciences, Myodaiji, Okazaki 444-8585, Japan. ytamura@nips.ac.jp
authors.forename: Yohei
authors.initials: Y
authors.lastname: Tamura
authors.forename: Minoru
authors.initials: M
authors.lastname: Hoshiyama
authors.forename: Koji
authors.initials: K
authors.lastname: Inui
authors.forename: Hiroki
authors.initials: H
authors.lastname: Nakata
authors.forename: Toshiaki
authors.initials: T
authors.lastname: Wasaka
authors.forename: Shiro
authors.initials: S
authors.lastname: Ojima
authors.forename: Kiyoharu
authors.initials: K
authors.lastname: Inoue
authors.forename: Ryusuke
authors.initials: R
authors.lastname: Kakigi
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D003071:Cognition / Q000502:physiology*; D004192:Discrimination, Psychological / Q000502:physiology*; D004558:Electric Stimulation / Q000379:methods; D005073:Evoked Potentials, Somatosensory / Q000502:physiology*; D006801:Humans; D008297:Male