Inter- and intrahemispheric differences in the peak frequency of rhythmic activity within the alpha band.

EEG was recorded simultaneously from several scalp regions in 5 normal subjects and analysed, using a PDP 11/45 computer by means of an autoregressive model. Significant intra- and interhemispheric differences in the peak frequencies within the alpha band were observed, up to 0.8 c/sec. Local modality -dependent increases in the peak frequency were also observed, which were predominant in occipital areas during visual stimulation and in central regions during acoustic stimulation. In most cases an increase in the peak frequency occurred together with a marked decrease in power, which could be interpreted as a desynchronization of slow components within the alpha band. These peak frequency differences found in the scalp EEG lead to the assumption that there might also be different alpha rhythms at the level of the cortex.