EEG alpha rhythms and transient chromatic and achromatic pattern visual evoked potentials in children and adults

Abstract

Transient chromatic pattern visual evoked potentials (VEPs) have been found to be less repeatable in morphology in children than in adults at low to moderate chromatic contrasts. The purpose of this study is to investigate whether low repeatability of VEP components can be associated with high alpha power, in a comparison of alpha activity in children and adults. Transient chromatic contrast and achromatic resolution VEPs were recorded in children (n=14, mean 9.6years) and adults (n=12, mean 21.8years) with normal vision and assessed for repeatability. Isoluminant chromatic (magenta-cyan) and luminance-modulated achromatic grating stimuli were presented at and above psychophysical threshold levels, in pattern onset-offset at 2Hz temporal frequency. EEGs (eyes closed and open) were recorded as single sweeps (1s long) over three 30s periods while facing a uniform computer display. An index of VEP detectability by observation was developed based on VEP component repeatability. The index was examined for correlations with alpha-wave parameters. Alpha power was calculated as the sum of the powers of 8-13Hz frequencies of the EEG sweeps (using the discrete Fourier transform). Alpha power variability was calculated using the standard deviation of the powers of each sweep in a 30s time period. The children had significantly higher alpha powers than the adults for both the eyes-open and eyes-closed conditions. Alpha power variability was significantly higher for the eyes-open condition only. There was no relationship between alpha power parameters and index of VEP detectability by observation for both the chromatic and achromatic grating stimuli. Poor repeatability of transient pattern VEPs is not associated with high alpha power or its variability in EEG measurements in older children or young adults at Oz.