The use of evoked potentials in sleep research

Abstract

Averaged event-related potentials (ERPs) represent sensory and cognitive processing of stimuli during wakefulness independent of behavioral responses, and reflect the underlying state of the CNS (central nervous system) during sleep. Components measured during wakefulness which are reflective of arousal state or the automatic switching of attention are sensitive to prior sleep disruption. Components reflecting active attentional influences during the waking state appear to be preserved in a rudimentary form during REM sleep, but in a way that highlights the differences in the neurochemical environment between wakefulness and REM sleep. Certain ERP components only appear within sleep. These begin to emerge at NREM sleep onset and may reflect inhibition of information processing and thus have utility as markers of the functional status of sleep preparatory mechanisms. These large amplitude NREM components represent synchronized burst firing of large number of cortical cells and are a reflection of the nervous system's capacity to generate delta frequency EEG activity. As such they are useful in assessing the overall integrity of the nervous system in populations not showing substantial amounts of SWS as measured using traditional criteria. While requiring care in their interpretation, ERPs nonetheless provide a rich tool to investigators interested in probing the nervous system to evaluate daytime functioning in the face of sleep disruption, the ability of the sleeping nervous system to monitor the external environment, and the ability of the nervous system to respond to stimuli in a manner consistent with the initiation or maintenance of sleep.

Figure 1

Grand-average ERPs following presentation of frequently occurring standard tones (dotted line), and rarely presented target tones (dashed line) and novel, environmental sounds (solid line) are illustrated. Two different groups of subjects were tested, control subjects who were not sleep deprived (NSD) and a totally sleep deprived (TSD) group. The TSD group was also recorded following recovery sleep (RS). From with permission. Negativity at the scalp relative to the reference is traced as an upward deflection in this and all other figures.

Figure 2

The error-related negativity (ERN) following normal sleep and sleep deprivation. Trials were time-locked to the response and then averaged. The grand average of the trials in which correct (thin line) and incorrect-error decisions (thick line) were made is illustrated. From , with permission.

Figure 3

Grand mean waveforms during wake, stage 1 alpha, stage 1 theta and stage 2 sleep recorded at Cz (upper panel) and Pz (lower panel). Voltage is plotted on the y-axis in microvolts. Negativity at the scalp relative to the reference (linked ears) is shown as an upward deflection. The data highlight the appearance of an N350 (labeled N300 in the figure), maximal at Cz, when stimuli presented within stage 1 sleep occur during a brief period of theta activity. The Pz panel highlights the presence of a P300 (labeled P3) to rare target tones during wakefulness, that persists into stage 1 alpha, but is replaced by the N350 with the onset of theta activity. Adapted from with permission.

Figure 4

Averaged auditory ERPs from stage 2 NREM sleep in young (dark lines) and elderly (light lines) healthy subjects, adapted from with permission. Data are presented from Fz (upper panel) and Cz (lower panel) electrode sites, and are based on the averages of only those responses containing K-complexes (KC+). The waveforms display small P50 (middle latency) and N1 components, and a prominent P2, that is larger in the elderly. N350 is more prominent at Cz, and N550 more prominent at Fz.