Effects of age upon interhemispheric EEG coherence in normal adults

Age related differences in quantified electrophysiological measures of interhemispheric EEG coherence were studied in 371 subjects (171 males and 200 females), ages 20-80, all of whom were judged to be optimally healthy. Principal components analysis (PCA) was performed on interhemispheric coherence of Laplacian referenced data from eight homologous left-right electrode pairs, from 0.5 to 32 Hz. Regression procedures, using signals from artifact monitoring channels, were used to minimize effects of eye movement and muscle artifact. Forty-six factors described 80% of the total variance, with electrode location the primary source of communality in factor formation. Within 350 right-handed subjects, results indicated a broad trend for decreased interhemispheric coherence with advancing age. Using canonical correlation, the coherence-based factors also successfully predicted spectral variables, previously found to maximally illsutrate age- related EEG desynchronization. We speculate that age-related reduction of interhemispheric coherence may in part explain age-related EEG desynchrony and stems from age-related reduction of cortical connectivity. Gender differences in interhemispheric coherence were also evident. Females demonstrated higher interhemispheric coherence than males. Within a smaller subpopulation of 63 subjects (21 left and 42 right handed), there was a gender-by-handedness interaction, with higher interhemispheric coherence in right-handed females than right-handed males and the reverse in left-handed male and female subjects.