[Ultradian periodicity, diurnal and circannual rhythms in the electroencephalogram]

The cerebral rhythms depictable by the EEG show fluctuations with several characteristic periodicities. The ultradian region with a range from several seconds to 20 hours is divided into three sections. Pathological and physiological EEG-characteristics are influenced by physiological rhythms of 2-100 seconds. The EEG-complexes occurring with panencephalitis are dependent on breath frequency. Grouped dysrhythmias correlate with higher order blood pressure waves. Systematic changes of the basal activity caused by slow variations of direct voltage have been conjectured by Aladzhalova (1964) and confirmed by spectral analysis (K unkel et al. 1969). Periods of 60-140 minutes with a medium cycle of approximately 90 minutes are typical for sleep, the phases of which are shown by the EEG and the recording of rapid eye movements (REM). THe periodicity corresponding to the basic rest activity cycle can also be shown on the EEG in a state of awakeness . Diurnal studies between sunrise and sunset showed frequency variations of some pathological EEG characteristics. The frequency of abnormal rhythms increased evenly from 8 am to 3.8% to 3 pm to 9.5%. Grouped dysrhythmias showed similar effects. As far as basal activity is concerned the occurrence of a diurnal peak of measurements in the alpha range and their maxima in the high frequency ultradian regions was noticeable. Circadian studies with a periodicity of 24 (plus/minus 4) hours showed that the diurnal maxima of all frequency ranges occurred almost simultaneously, however, they contained temporal shifts due to their specific structure. The major pertinent differences were shown by frontal and temporobasal cerebral areas. Circadian studies of sleep phases of primates showed a maximum for delta activity at 1 am and for theta activity at 5 am. As expected, circannual rhythms of hibernating animals can be observed on the EEG, they have also been discovered with humans be means of EEG measurements: by visually analyzing EEG results, systematic differences in the frequency of types of basal activity were noticed. Thus, Beta-EEGs with a medium frequency of 14% occurred in May with the frequency of Alpha-EEGs fluctuated in inverse proportion and was at its peak during summer. Conspicuous among pathological EEG characteristics were grouped dysrhythmias that occurred about twice as often in summer as in winter. No generally valid cause can be assumed for the variety of rhythms.