Crossmodal interaction is reflected in vertex potentials but not in evoked magnetic fields.

Magnetic responses and slow vertex potentials evoked by tone bursts and median nerve shocks were recorded in healthy humans to study crossmodal interaction. Stimuli were presented either alone, simultaneously or in pairs separated by 0.5 s; the interstimulus interval was 5 s. Simultaneous or preceding stimuli of another modality did not influence the amplitudes of the magnetic responses, which are known to be generated at modality specific projection areas. However, the electric vertex potentials decreased in amplitude in similar situations, suggesting that the electric and magnetic responses reflect neural events of at least partly different brain areas. Our results do not give support for crossmodal interaction at the sensorimotor or auditory cortices.