A comparative study of alpha responses in human occipital EEG recordings and in cat intracranial EEG recordings

According to a working hypothesis published earlier [1], evoked potentials (EPs) are considered as stimulus-induced EEG rhythmicities. This approach was used to study topography- and modality-dependent differences of auditory and visual EPs. Scalp recordings from 11 healthy volunteers and intracranial recordings from 6 cats were compared. Occipital recordings in humans showed a marked alpha (8–15 Hz) response to visual stimulation. In comparison, responses to acoustical stimulation were markedly reduced. Findings in cat intracranial recordings were similar. Both in cats and in humans, inter-modality differences were smaller for theta responses. A functional differentiation of alpha and theta components is conceivable: the alpha response might be more closely connected to primary sensory processing than the theta response. It is remarkable that comparable findings have been obtained in MEG measurements.