Maturational changes in the electroencephalogram of normal monkeys

Abstract

Electroencephalographic activity (EEG) was recorded between birth and 30 months on rhesus monkeys of known gestational age, delivered vaginally or by section. Restraint with minimal disturbance reduced movement artifacts. Electrodes were applied to the scalp overlying frontal, parietal, occipital, and temporal brain areas. Photic stimulation also was used. Interpretation of the EEG patterns was based on monopolar (ears as reference) and bipolar recordings while awake, during drowsiness, and asleep. The EEG during wakefulness in the first month showed low-voltage, slow waves in all areas, with faster frequencies superimposed, and remained basically the same as on the first day. During the second month a marked change in amplitude and rhythm occurred, showing generalized high-voltage sinusoidal waves. As the animal matured (1 year) a trend toward lower voltages and faster frequencies developed. The EEG pattern showed differences between wakefulness and sleep from the first day of life. Voltages were generally higher during sleep, especially in the parietal and frontal areas. Hump and spindle phases, comparable to those in the human, were clearly defined. Sharp “spikes” appeared in the parietal leads about the beginning of the first week; these could be misinterpreted as seizure discharges. The greatest changes in the EEG patterns occurred in a relatively short period after birth, after which they became stabilized into the adult forms.