Relationships between brain morphology and behavioral measures of hemispheric asymmetry and interhemispheric interaction

Abstract

Thirty adult males identified consonant-vowel-consonant nonword trigrams projected briefly to the left visual field (right hemisphere), the right visual field (left hemisphere) or to both visual fields (and hemispheres) simultaneously. Magnetic resonance images of the brains of these same individuals provided measurements of the length of the Sylvian fissure and surface area of the planum temporale within each hemisphere as well as measurements of the midsagittal area of the corpus callosum. Both behavioral and morphological asymmetries were consistent with those found in previous studies. In addition, there were several relationships between brain morphology and trigram naming. For example, as the length of the right-hemisphere Sylvian fissure increased to become more like the typical length of the left-hemisphere Sylvian fissure, there were fewer errors of trigram identification and attention was distributed more quickly or evenly across the three letters contained in the display. In addition, as the midsagittal area of the corpus callosum increased, the percentage of errors increased on left visual field trials, but not on right visual field or bilateral trials, suggesting that an increase in corpus callosum size may be indicative of greater functional isolation of the two hemispheres.