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M. Boon, K. Chan, J. Chiang, R. Milston; EEG Alpha Rhythms and Transient Chromatic and Achromatic Visual Evoked Potentials in Children and Adults. Invest. Ophthalmol. Vis. Sci. 2010;51(13):1508.
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© ARVO (1962-2015); The Authors (2016-present)
Transient chromatic visual evoked potentials (VEP) have been found to be less repeatable in morphology in children than in adults at low to moderate chromatic contrasts. EEG alpha wave activity is usually stronger when the eyes are closed and attenuated when the eyes are opened in adults. However, there have been reports that attenuation does not always occur in children on eye opening so alpha activity could obscure morphology of VEP recordings of children. Therefore, the purpose of this study is to compare alpha activity in children and adults and its relationship with VEP repeatability.
Transient VEPs were recorded in children (n=14, mean: 9.6 years, range: 5-13.3 years) and adults (n=12, mean: 21.8 years, range:20-22 years) with normal vision. Chromatic stimuli were isoluminant magenta-cyan gratings at psychophysical and suprathreshold chromatic contrasts. Achromatic stimuli were black and white gratings (100% contrast) at psychophysical threshold and suprathreshold spatial frequencies. Both chromatic and achromatic stimuli were pattern-onset with a temporal frequency of 2 Hz. Alpha waves were recorded at Oz (referenced to Cz, earth Fz) in both the eyes closed and open conditions while facing a blank computer monitor. Alpha power was defined as the sum of the powers of 8-13Hz frequencies as assessed using Fourier analysis. Percentage alpha power attenuation on eye opening was also assessed.
Alpha power (eyes open and closed) was higher in children than adults (p<0.022). Alpha attenuation did not significantly differ between adults and children. There was a linear relationship between transient chromatic VEP repeatability and alpha power when the eyes were open (ANOVA, Beta=0.71, p=0.004) and closed (ANOVA, Beta=0.64, p=0.014) in the children but not in the adults. There was a linear relationship between transient achromatic VEP repeatability and alpha power when the eyes were open (ANOVA, Beta=0.45, p=0.022) in adults only.
Higher alpha powers in the eyes open condition are associated with less repeatable morphology of chromatic VEPs in children so should be considered in any clinical assessment of transient VEP morphology. In contrast, transient achromatic VEPs in children are highly repeatable, even at psychophysical threshold suggesting that alpha activity differentially affects chromatic and achromatic processing.
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