Frequency analysis of the human electroencephalogram during the performance of a discrimination task

The EEG in five frequency bands was studied in the occipital and frontal areas of two subjects performing a behavioral task. Each trial of the task was divided into pre-stimulus, stimulus, and post-stimulus periods, with a duration of 10 seconds each. All trials demonstrating activity which was thought to be of muscular origin were discarded. The resulting data showed the following: (1) Activity at 20 Hz was consistently lower during the stimulus period in the occipital electrodes. (2) Activity at 40 and 50 Hz increased in the occipital derivation during the stimulus period in both cases. (3) None of the comparisons showed any significant changes in the F3-Fz derivations. Tentative hypotheses were advanced relating the decrease in 20 Hz to behavioral "inhibition" and the increase in 40 and 50 Hz to "facilitation" or possibly "orientation". It was suggested that these data might also be interpreted as electrical corollaries of short term memory processes.