Quantitative analysis of cerebral asymmetries. Fronto-occipital correlation, sexual dimorphism and association with handedness.

To investigate the biological and functional significance of cerebral asymmetries, we measured lateral differences of the frontal and occipital poles on computed tomographic scans of 66 adult outpatients with no diagnosed abnormalities. In addition to confirming the greater average sizes of the right frontal and left occipital poles, we found a significant linear correlation relating anterior and posterior difference measures. Men showed greater degrees of frontal and occipital asymmetries than women; reversals of the typical asymmetries were more common among women. Reduction or reversal of the usual left occipital predominance in the presence of typical right frontal predominance was associated with non-right-handedness. These findings clarify and extend prior qualitative observations and relate to the possible role of testosterone in modulation of cortical asymmetries. Reduced structural asymmetries among women and non-right-handers may provide an anatomical basis for clinical and laboratory findings of lessened functional lateralization in these groups.