Degree of handedness and cerebral dominance

Objective: To examine the relationship between the degree of handedness and hemispheric language dominance in patients with epilepsy. Methods: The authors examined the relationship between degree of handedness and hemispheric language dominance in 174 epilepsy surgery candidates using the intracarotid amobarbital procedure and results from a modified version of the Edinburgh Handedness Inventory. Results: The incidence of atypical language dominance increased linearly with the degree of left-handedness, from 9% in strong right-handers (laterality quotient [LQ] = +100) to 46% in ambidextrous individuals and 69% in strong left-handers (LQ = -100). Conclusions: The incidence of atypical language dominance depends not only on the direction but also on the degree of handedness. In addition, direction of language dominance varies with hemisphere of seizure focus and degree of handedness. A familial history of sinistrality may have an additional effect on the likelihood of atypical dominance.