Amplitude of evoked potentials and degree of event-related desynchronization (ERD) during photic stimulation.

The variations in amplitude of visual evoked potentials (VEPs) and parallel changes in amount of event-related desynchronization (ERD) of the rhythmic activity within the alpha band were studied in central derivations of scalp EEG, in 10 normal subjects. Two methods were used to estimate the amplitude of VEPs in small groups of 10 responses: (1) inverse and matched filtering techniques; (2) two-way rank analysis of variance by the Friedman test. The two methods gave similar results and two groups, statistically different, emerged. The first, with large VEP amplitude, having at the same time large ERD, and the second, with small VEP amplitude and small ERD.