Abstract: 1. The influence of mental activity on EEG was investigated on 359 subjects, 164 males and 195 females ranging from 4—86 years of age, EEGs were recorded on an 16-channel Ediswan-Ⅲ EEG machine. Subjects were requested to mantain a relaxed position with eyes closed in a dark room. After familiarization with the routine some arithmetic problems were given at 5—10 min. intervals. Results showed that during mental activity a variaty of patterns of EEG alterations was existed and a-blocking was not the only concomitant of mental calculation.2. Subjects ranging in ages between 4—86 years showed different EEG alterations during mental activity. Frequently no EEG modification was found between 4—7 years of age, more and more EEG modifications were noted with the increase of age. θ-waves were more frequently observed between 8—17 years of age and diffusely α-blocking over the whole cortex was most marked in Ss between 18—60 years of age.3. EEG alterations, associated with mental calculation, were localized mainly in the temporal (mostly the left temporal) and frontal regions in Ss of different ages.

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