[Effect of mental fatigue induced by repeated continuous calculation tasks on event-related brain potential (P300)]

It is well known that the amplitude and latency of P300 in event-related brain potentials (ERPs) evoked by performing the oddball paradigm reflect the extent of individuals' selective attention. The purpose of this study was to examine whether P300 is a reliable measure for evaluating mental fatigue. In addition to the measurement of auditory ERPs derived from Fz, Cz and Pz, the concentrations of lactic acid, cortisol in plasma and the reaction time of the oddball paradigm, which are believed to reflect fatigue, were measured. In an attempt to cause mental fatigue, 12 healthy college students (8 males, 4 females; 19.5 +/- 0.5 yr; mean +/- S.D.) were forced to perform a continuous addition task using the Uchida-Kreperin test paper for about 2 h. Before the task, the latencies of P300 in Fz, Cz and Pz were 295.6 +/- 8.7 msec, 298.8 +/- 8.5 msec and 297.5 +/- 7.2 msec (mean +/- S.D.), respectively, and after the task they were 312.6 +/- 11.2 msec, 314.6 +/- 10.1 msec and 315.8 +/- 8.7 msec, respectively. A significant difference in the latency before and after the task was detected (p<0.01). In all subjects, the latency of P300 was prolonged in all recording positions, Fz, Cz and Pz. In a control experiment where the continuous addition task was not loaded, a significant change of the latency was not detected. The amplitude of P300 didn't change significantly in all recording positions after the task. In the control experiment, the amplitude of P300 did not change significantly. On the other hand, the changes in the concentrations of lactic acid and cortisol and the reaction time were not induced by the continuous addition task. The prolongation of the latency of P300 would originate from a decline in brain function. In this study, a prolongation of the latency of P300 after the task was detected in all subjects. It is well known that the value of P300 changes with modification of the recording condition, therefore a recording of P300 under the same conditions is required for qualitative evaluation.