Hemispheric specialisation for imitation of hand-head positions and finger configurations: a controlled study in patients with complete callosotomy.
Several studies of patients with unilateral brain damage and a patient with spontaneous callosal disconnection [Journal of Neurology, Neurosurgery, and Psychiatry 61 (1996) 176; Neuropsychologia 37 (1999) 559; Neuropsychologia 39 (2001) 1432] suggest that the imitation of positions of the hand relative to the head is a strongly lateralised left hemispheric function. In contrast, the imitation of finger configurations draws on resources of both hemispheres with a predominance of the right hemisphere. While these findings suggest a specific pattern of imitation impairment in split-brain patients, thus far, no imitation deficits have been reported in split-brain patients. Three patients with complete callosotomy and two control groups, four patients with partial callosotomy and 10 healthy subjects, imitated hand-head positions and finger configurations with non-lateralised and tachistoscopic stimulus presentation. In addition, the influence of visual control on the imitation performance was examined. One split-brain patient showed the predicted dissociation as she had severe right hemispheric deficit in imitating hand-head positions, while finger configuration imitation was preserved. The other two split-brain patients had no impairment in hand-head position imitation. Withdrawal of visual control significantly deteriorated imitation of finger configurations in the split-brain group, but not in the controls, demonstrating that the split-brain patients relied heavily on visual control as a compensatory strategy indicating an imitation deficit in the separate hemispheres. The findings question the previously held belief that in split-brain patients both hemispheres are perfectly capable of imitating gestures and that imitation is not dependent on hemispherically specialised functions.
Lausberg
Hedda
H
Department of Neurology, Free University of Berlin, Hindenburgdamm 30, D-12200 Berlin, Germany. hedda@zedat.fu-berlin.de
Cruz
Robyn Flaum
RF
D000293:Adolescent; D000328:Adult; D000368:Aged; D001925:Brain Damage, Chronic / Q000503:physiopathology*; D003337:Corpus Callosum / Q000503:physiopathology*; D004292:Dominance, Cerebral / Q000502:physiology*; D005260:Female; D005385:Fingers; D005868:Gestures; D006225:Hand; D006257:Head; D006801:Humans; D007100:Imitative Behavior; D008875:Middle Aged; D010364:Pattern Recognition, Visual / Q000502:physiology*; D011597:Psychomotor Performance / Q000502:physiology*; D014794:Visual Fields