Academic journal article Canadian Journal of Experimental Psychology

EEG Characteristics Prior to and Following the Evoked K-Complex

Academic journal article Canadian Journal of Experimental Psychology

EEG Characteristics Prior to and Following the Evoked K-Complex

Article excerpt

Abstract This study was designed to determine if the KComplex reflects an arousal from sleep or a sleep protection mechanism. Ten participants were presented auditory stimuli every 20 s while asleep. Trials were sorted according to the presence or absence of a K-Complex. A fast Fourier Transformation of the data was computed on EEG segments prior to and following stimulus onset. The log power of activity in delta, theta, alpha, sigma, and beta bandwidths was computed. When a K-Complex was elicited, there were no differences in EEG activity prior to and following the stimulus. However, during slow wave sleep, when a K-Complex was not elicited, there was a significant overall increase in theta, alpha, sigma, and beta activity following stimulus. These results tend to support the notion that the K-Complex appears to prevent arousal.

During sleep, information processing from the external environment is largely inhibited by a thalamo-cortical loop gating system (Steriade, McCormick, & Sejnowski, 1993). All but the most relevant of information is gated from entry to consciousness, presumably to prevent sleep from being disturbed. It is thus somewhat of a paradox that the largest response to an external stimulus that can be recorded from the human scalp occurs during sleep. Because of its very large amplitude, it was first noticed in some of the earliest electrical recordings of the human sleep patterns using the newly discovered electroencephalogram (EEG) (Davis, Davis, Loomis, Harvey, & Hobart, 1939; Loomis, Harvey, & Hobart, 1939). This large amplitude response was labelled the K-Complex, for reasons that are still largely unknown. There is some belief (with little support) that it derived from the fact that a simple knock on an adjacent wall might elicit the K-Complex in the sleeper. Strangely, the K-Complex might be elicited by a stimulus one time and when the same, identical stimulus is later again presented, the K-Complex no longer can be elicited. At times, the K-Complex occurs spontaneously in the ongoing lEG in the absence of any apparent external stimulus. Of course, this does not necessarily mean that there was no stimulus. It is possible that the K-Complex might be elicited by internal consciousness or perhaps by something like an unobserved muscle twitch. Colrain and his colleagues have indicated that the K-Complex can be elicited by interruptions of breathing (Colrain, Bell, & Gora, 1998).

Most human evoked potentials recorded within conscious, waking, and alert states measure from 1 to 15 (mu)V. The K-Complex often exceeds 100 (mu)V. The K-Complex consists of a very large amplitude negative deflection peaking between 500 and 600 ms (thus the label, N550) followed by a positive wave peaking between 800 and 1,200 ms (P900) (Halasz, Pal, & Rajna, 1985; Ujszaszi & Halasz, 1988). The K-Complex appears as a phasic event: It is a transient EEG activity that occurs perhaps once every 2-3 minutes, although its frequency of occurrence can vary widely within and between sleepers. Sleep is conveniently divided into two markedly different states, REM (rapid eye movement) and non-REM. There are many differences between REM and non-REM sleep. Among the markers of non-REM sleep is the appearance of the K-Complex. In REM sleep, the K-Complex cannot be elicited by an external stimulus nor does it occur spontaneously. NonREM sleep is further subdivided into Stage 2, 3, and 4 of sleep, Stage 4 being associated with deeper sleep than Stage 2.

We now know a good deal about the types of stimuli and paradigms - the antecedent conditions - that will elicit the K-Complex. The K-Complex is most often elicited by a psychologically relevant stimulus, such as the participant's own name; or a biologically relevant stimulus, such as a relatively loud and abrupt tone that is presented infrequently. Altering the participant's ability to breathe is obviously biologically relevant. This "stimulus" will elicit a K-Complex, even if the change in breathing occurs as often as every 5 s. …

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