Seasonal Variations of Cerebral Hemispheric Asymmetry

Abstract:
Seasonal variations of hemispheric asymmetries in glucose metabolism have been observed recently in the human cerebral prefrontal cortex, during PET studies with ¹⁸ FDG done in normal volunteers, residing in the east coast. Glucose metabolic rates of the right prefrontal region showed an inclination to be higher than the left in winter and lower in summer (Nordahl, Cohen 1997). Each subject was imaged only once, while performing an auditory CPT task in a darkened room wearing eye patches. The purpose of the present study, was to test the replicability of the above findings in a small group of normal subjects, living in a different climatic and time -zone (West Coast), performing a Stroop mental task, while data is acquired with a high-resolution, single-slice, MRI- registered, PET tomograph. Metabolic rates were calculated in multiple ROIs. An index of hemispheric asymmetry between right (R) and left (L) corresponding areas was calculated as the ratio of (R-L) to (R+L) in each region. Analyses of variance was used to evaluate the statistical significance of a difference between summer and winter subjects groups. A significant (p<0.05) seasonal variation was found only in the antero-medial part of the prefrontal cortex, with hemispheric asymmetry indices (mean ± s.d.) of ~0.016 ± 0.026 for summer and 0.030 ± 0.035 for winter. No significant seasonal variation was detected in any of the multiple other brain ROIs, including more inferior portions of the prefrontal cortex, temporal and parietal gyri, the cingulate gyrus, the hippocampus, the thalamus and the basal ganglia.