K-complex formation of the EEG in sleep. A survey and new examinations

The first part of the work offers a survey of the literature on the K complex. In the second part the authors' own investigations are discussed. The data come from three series of experiments: 1) from five sleeps of eight subjects (s) observed under different experimental conditions: 2) from twenty-one nights spent without stimulation and fourteen nights at acoustic stimulation of the same s; 3) from the analysis of the K complexes appearing in stimulated and non-stimulated periods alternating every five minutes of stages 2 in the first cycles of 6 sleeps of another s. In five sleeps of an identical s the K complexes were examined also by means of averaging. The frequency of the K complexes was greater in the stages 2 ascending type than in those of descending type. Sensory stimulation increased the formation of K complexes in the ascending slopes of the cycles to a higher degree than in the descending ones. Repression of the K complexes appearing on the effect of stimulation in the ascending slope was more marked than in the descending one. These findings indicate a close connection of the formation of K complexes and phasic sensory activation. At the same time a connection between K-complex formation and the measure of sleep synchronization was observed. From evening to morning the frequency of K complexes decreased from cycle to cycle, parallel with the decrease in the depth of sleep. Similarly, the frequency of the K complexes measured in stages 2 showed a relationship with the depth of the cycles: the deeper the sleep in the given cycle, the more the K complexes found in unit time in stages 2 belonging to the cycle anchoring the measured stage 2. The EEG responses that could be identified with K complexes elicited by means of acoustic stimuli could be demonstrated by averaging in the whole slow-wave sleep. It is assumed that the EEG phenomena of K complex-type of spontaneous sleep arise under the effect of continuous sensory activation, hence they correspond with nonspecific evoked potential elements, and therefore the K complex can be regarded as a building stone of slow-wave sleep. At the same time K complexes were interpreted as conflict products of sensory activation and sleep-protecting influences and considered important indicators of the dynamics of the sleep-waking system.