The form, voltage distribution and physiological significance of the K-complex

Abstract

1. 1. A study has been made of the morphological features of the K-complex during consciousness, sleep, and barbiturate anaesthesia, in 80 psychiatric patients and 15 normal subjects. No differences between the two groups of subjects came to light. During consciousness the phenomenon is elicitable in about 20 per cent of subjects but is prominent only in about one-third of these. 2. 2. To the “sharp wave” component, the only one clearly discernible in the awake subject, there are added in unconsciousness one or more high voltage slow waves followed by a burst of “spindles”. Both the latency and the duration of the sharp wave component are increased during sleep and barbiturate anaesthesia. In these and other states of diminished awareness the phenomenon is universally present; it is abolished in deep unconsciousness. 3. 3. Evidence is presented suggesting that the K-complex is specially adapted for responding to transient disturbances in the environment. Swift adaptation occurs to continual stimuli; those given at shorter than 2–3 sec. intervals in sleep are interpreted as continual. Different forms of stimulation evoke identical K-complexes. 4. 4. Studies of the voltage distribution of the K-complex by a special technique reveal congruent distributions during both first and second components which are consistent with the activity of a stationary source or sources. The widespread distribution of these two phases in hence attributed to their being mediated by some diffuse projection system to the cerebral cortex. 5. 5. Attention is drawn to the similarities between the K-complex with its initial electropositive deflection and after-discharge, and the localised changes of smaller voltage evoked in specific sensory areas by various types of afferent stimulation. The K-complex is however distributed over a diffuse area and is identical for different stimuli. There is evidence to suggest that it is the correlate of a crude perceptual process which tends to initiate arousal. Such a theory satisfactorily accounts for the known facts about the complex: its non-specificity, diffuse distribution, and its presence in prominent form only in states of inconsciousness.