On P300 measurement stability: habituation, intra-trial block variation, and ultradian rhythms

P300 event-related brain potentials (ERPs) were elicited using a simple dis crimination task in which participants discriminated two different equiprob able visual stimuli with button-press responses (n = 20). A total of ten tr ial blocks were presented at 10-min intervals. P300 amplitude declined sign ificantly, but peak latency did not change reliably across trial blocks. P3 00 amplitude demonstrated a reliable cyclical fluctuation across trial bloc ks, although P300 latency did not. Intra-trial block ERP variability was as sessed by computing the correlation coefficients between the target and sta ndard stimuli for amplitude and latency measures across participants within each trial block. P300 amplitude correlations were weakest at the Fz elect rode, more strongly associated at Ct, and were most strongly correlated at Pt across trial blocks. P300 latency correlations were somewhat weaker and similar in strength across electrodes sites. The correlational patterns for both P300 amplitude and latency demonstrated reliable cyclical variation. The N100 component produced strong and consistent correlations for both amp litude and latency, whereas the P200 and N200 component measures evinced cy clical correlational patterns similar to the P300 across trial blocks. Thes e results suggest that the stability of P300 and other component measures c an vary appreciably within and across trial blocks in a manner that reflect s ultradian variation in arousal level. (C) 1999 Elsevier Science B.V. All rights reserved.