Atypical speech is rare in individuals with normal developmental histories.

The prevalence of atypical (right, bilateral) speech lateralization is unknown in normal populations. The authors investigated this by studying people with normal developmental histories but a later, specific adult neurologic event leading to intractable epilepsy. Fifty of 836 people receiving intracarotid amobarbital procedures (IAPs) met criteria of normal neurologic histories through age 15 years, with later head trauma or cerebral infection as probable cause of subsequent epilepsy. All 50 patients had left hemispheric speech on IAP. Atypical speech lateralization is rare unless there is also a positive neurologic history.