Evidence for the pathological right-handedness hypothesis.

The present study investigated handedness of 109 Korean patients with temporal lobe epilepsy (TLE) and 120 normal control participants. Left TLE was associated with a significantly raised incidence of left-handers relative to normal controls. More important for the present purpose, right TLE was associated with a significantly raised incidence of strong right-handers relative to normal controls. This finding indicates that certain early damage to the right brain causes a mild hypofunction of the left hand in natural weak right-handers, which in turn causes the patient to switch to strong right-handedness. To the authors' knowledge, this finding provides the 1st empirical evidence supporting the pathological right-handedness hypothesis. Prior failure to find evidence of pathological right-handedness may reflect the low base rate of natural left-handers rather than true absence of pathological right-handers.