The distribution of 40HZ. EEG activity in normal children



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The electrical activity in three frequency bands in the 'arousal spectrum' was studied in the right and left occipital, parietal and frontal areas of 22 normal male children (age, M=10.18, SD=0.92; IQ, M=102.36, SD=4.63) during a verbal-visual behavioral task and during a rest control. Percent-time of activity was computed with a special purpose analog computer for 31.5, 40 and 50 Hz. bands. A 70 Hz. band was used as an Indication of muscle potential. Trials that Indicated contamination by muscle potentials were excluded from further analysis. The results were; 1) Percent-time of 40Hz. decreased significantly in both occipital leads, increased significantly in P[lowered 4] and approached a significant increase in P[lowered 5]. There was no Increase or decrease in the frontal leads. 2) Percent-time of 31.5 Hz. decreased significantly in all leads. 3) Percent-time of 50 Hz. Increased in the parietal leads but neither 31.5 nor 50 Hz, covaried significantly with 40 Hz. across conditions. 4) Percent-time activity was found to be greater on the right side of the head in only the 31.5 Hz. frequency band and only in the occipital and frontal leads. The other leads and frequencies showed no asymmetries. The results were interpreted within a framework of a narrow frequency band in the EEG centered at 40 Hz. which reflects a limited cortical excitability for maintaining sequences in short-term memory store.