Statistical analysis of this distribution shows that concordance between the dominant hemisphere
for handedness and that for language is random, except for a small fraction of the population (less than 1 percent) for whom the right hemisphere is dominant for both language and handedness.
While activation patterns are widely distributed through these patients' dominant hemispheres
, areas crucial for expressive and receptive language function can be isolated and reliably mapped.
The dominant hemisphere
, which is usually the left in right-handed people, and vice versa, contains the speech centre, known as Broca's area.
Risk factors identified for this verbal memory decline include later age of epilepsy onset, higher memory performance at baseline, dominant hemisphere
resection, no clear asymmetry of memory function during testing, and an absence of clear structural abnormalities of the mesial temporal structures on the side being considered for resection.
This may reflect myelination differences in the dominant hemisphere
of normal right-handed children which may be lost after frontal lobe injury.