[Event-related potentials and performance errors during falling asleep].

Sound is the most adequate external stimulus for studying information processes in the brain during falling asleep and at different sleep stages. Common procedure of analysis of the event-related potentials (ERPs) averaged for a group of subjects has some drawbacks because of the ERP interindividual variability. Therefore in our work, we determined parameters of the auditory ERP components selectively summed up for individual subjects in different series of a psychomotor test with their subsequent group analysis. Search for the ERP parameters which would allow us to quantitatively estimate brain functional states during performance errors associated with a decrease in the level of wakefulness and falling asleep was the aim of our work. The ERPs were recorded in healthy volunteers (n = 41) in the evening from eight EEG derivations (F3, F4, C3, C4, P3, P4, O1, O2) in reference to a linked mastoid electrode. The analysis was performed in 14 subjects with a sufficient number of falling asleep episodes. A monotonous psychomotor test was performed in a supine position with the eyes closed. The test consisted of two alternating series: calculation of sound stimuli from 1 up to 10 with simultaneous pressing the button and calculation from 1 up to 5 without pressing the button and so on. Computer-generated sound stimuli (50-ms pulses with the frequency of 1000 Hz, 60 dB HL) were presented binaurally through earphones with interstimulus intervals in 2.4-2.7 s. Comparison of the ERP parameters (latency and amplitude of components N1, P2, N, and P3) during correct and erroneous performance of the psychomotor test showed that a decrease in the level of wakefulness caused a statistically significant increase in the amplitude of components of vertex complex N1-P2-N2 in series without pressing the button. The greatest changes in the ERPs in different series of the psychomotor test were observed for component N2 (latency 330-360 ms), which has the common origin with the EEG theta rhythm and is characteristic of the first sleep stage.