Effects of ageing on multichannel steady-state visual evoked potential

Steady-state evoked responses combined with Fourier analysis permit a faster collection and evaluation of data than transient evoked potentials in all the three sensory modalities. Steady-State Visual Evoked Potentials (SS-VEPs) induced by applying flickering flashes of light were recorded in a group of young and a group of elderly normal volunteers. The aim of the study was twofold: a) to implement a method for a quick routine analysis of the visual function; b) to verify the effects of ageing on different parameters of SS-VEPs. The 14 subjects were divided into a younger group (mean age 21.5 ± 2.6 years) and an elderly group (mean age 64.6 ± 5.1 years). Each of the subjects had a normal or corrected visual acuity of or better. The flashes, which lasted 0.1 ms, were presented binocularly on a stroboscope in a partially darkened room, at the frequencies of 4, 6, 8, 12 and 16 Hz, for epochs of 10 s. The EEG was recorded from 20 electrodes (10-20 International System) referred to linked mastoids. The signals were analysed off-line by means of a software package developed in our laboratory for the Fourier analysis of biological signals. The following parameters were calculated: spectral moments of orders 0, 2 and 4; barycentric frequency; Hjorth's parameters; intra- and inter-hemispheric correlations and coherences; mean deviations of the amplitudes of the various Fourier harmonics over the 10 s epochs.