Theta and beta rhythm in the electroencephalograms of normal adults.

Abstract 1. 1. Low voltage theta activity was detected in 64 per cent of a group of 161 young normal adults and in 24 per cent of 50 mentally normal seniles, the differences between the two groups being significant at the one per cent level. This decrease of theta incidence with increasing age was discussed in relation to maturation processes. Evidence was further presented to indicate that theta activity in the senile group represented a different phenomenon from that encountered in the younger group. 2. 2. Variations in theta activity during either visual and/or mental tasks, or during slight changes in temper were observed in 26 per cent of the subjects showing theta rhythm in the younger group. Two classes of activity were differentiated, those harmonically related to alpha frequencies and those not. Observations on the theta variation appeared to accord with Walter's findings (1950, and in Hill and Parr 1950, chap. VII) in respect of theta rhythm and emotional level. Indcidence of theta rhythm was significantly greater among females than males. 3. 3. Low voltage beta activity was observed in cent of the senile group, the difference not being significant. Aplitudes were significantly greater in the older however. 4. 4. Fifty one per cent of those with beta activity in the younger group showed variation of beta rhythm with either visual and/or mental activation. Evidence was presented to suggest that beta activity may in part at least represent accelerated rhythms resultant on scansion of cortical projection and association areas. A highly significant relationship between beta incidence and alpha type was found to support this hypothesis, although the study needs repetition with the aid of automatic frequency analysis before certainty can be established. 5. 5. A significantly greater incidence of beta activity was found in the females as compared with the males of the younger group, whilst in the senile group a significantly greater incidence was found in a group of Europeans as compared with a group of Africans. These findings were briefly discussed in relation to cultural influences on the EEG.