Hemispheric asymmetries of limb-kinetic apraxia

Objectives: Unlike patients with ideomotor apraxia who make temporal and spatial errors and patients with ideational or conceptual apraxia who make content errors, patients with limb-kinetic apraxia have loss of deftness, including fine and precise movements, independent finger movements, and difficulty coordinating simultaneous movements. This study was conducted to learn the relationship between limb-kinetic apraxia and hemisphere dysfunction by using selective hemisphere anesthesia, the Wada test. Methods: Subjects were 90 patients undergoing Wada testing for intractable epilepsy. They were divided into typical (right-handed with left hemisphere language dominance) and atypical (nonright-handed, or without left hemisphere language dominance). Before and during Wada testing, subjects were shown line drawings of tools, four for each hand tested. After being shown each picture, subjects pantomimed the use of this tool. A behavioral neurologist and neuropsychologist scored the pantomimes for the presence of limb-kinetic errors. Results: For the typical group, during left hemisphere anesthesia, the limb-kinetic errors made by the right and left hands did not differ, but during right hemisphere anesthesia the left hand made more errors than the right. Unlike the typical subjects, when the left hemisphere was anesthetized, the atypical subjects made more errors with their right hands than left. However, similar to the typical subjects with right hemisphere anesthesia, the atypical subjects made more left- than right-hand limb-kinetic errors. Conclusions: For people with typical brain organization, the left hemisphere mediates motor deftness for both hands, but the right hemisphere primarily controls deftness for the left hand. For people with atypical brain organization, each hemisphere primarily controls deftness for the contralateral hand.