Bisensory stimulation increases gamma-responses over multiple cortical regions

In the framework of the discussion about gamma (approx. 40 Hz) oscillations as information carriers in the brain, we investigated the relationship bet ween gamma responses in the EEG and intersensory association. Auditory evok ed potentials (AEPs) and visual evoked potentials (VEPs) were compared with bisensory evoked potentials (BEPs; simultaneous auditory and visual stimul ation) in 15 subjects. Gamma responses in AEPs, VEPs and BEPs were assessed by means of wavelet decomposition. Overall maximum gamma-components post-s timulus were highest in BEPs (P<0.01). Bisensory evoked gamma-responses als o showed significant central, parietal and occipital amplitude-increases (P <0.001, P<0.01, P<0.05, respectively; prestimulus interval as baseline). Th ese were of greater magnitude when compared with the unisensory responses. As a correlate of the marked gamma responses to bimodal stimulation we sugg est a process of 'intersensory association', i.e. one of the steps between sensory transmission and perception. Our data may be interpreted as a furth er example of function-related gamma responses in the EEG. (C) 2001 Elsevie r Science B.V. All rights reserved.