Lateralised motor control: hemispheric damage and the loss of deftness. (Paper).

Objective: To learn if the left compared with the right hemisphere of right handed subjects exerts bilateral compared with contralateral motor control when performing precise and coordinated finger movements.

Methods: The study investigated intertask differences of manual motor asymmetries such as speed, precision, and independent finger movements, in patients with unilateral lesions of the left (LHD) or right hemisphere (RHD) and normal controls (C).

Results: Normal subjects showed the greatest right hand preference on a task that required rapid coordinated and precise independent finger movements (coin rotation). Both hemisphere damaged groups revealed contralateral motor deficits, but the magnitudes of asymmetries were found to be significantly different (RHD>C>LHD) with contralateral and ipsilateral deficits for LHD subjects. The greatest ipsilateral deficits for the LHD subjects were on those tasks that require precision (grooved pegboard and coin rotation).

Conclusions: The degree of hemispheric specialisation is, in part, dependent upon the nature of the motor task, with left hemisphere motor control necessary for tasks that require precision and coordinated independent finger movements.

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Hugo Liepmann (1 2) reported that hemispheric lesions, even in the absence of weakness, could be associated with a loss of the ability to perform skilled movements, apraxia. He described three forms of apraxia--ideomotor, ideational, and limb kinetic. When performing skilled movements patients with ideomotor apraxia make spatial and temporal errors. (3 4) When attempting to use a screwdriver, for example, instead of rotating the screwdriver on its axis they may rotate it so that the head moves in circles. Patients with ideational apraxia may be impaired in sequencing a series of acts that lead to a goal. For example, when making a sandwich, they may cut the sandwich in half before placing the meat between the bread. Ideational apraxia has also been used to describe patients who make content errors (for example, pound with a screwdriver and screw with a hammer). (5 6) To reduce confusing terminology, some investigators now call this second form of ideational apraxia, "conceptual apraxia". (6 7) According to Li epmann, (1 2) patients with limb kinetic apraxia have slowed and stiff movements and, when attempting to perform skilled acts, their movements are coarse and clumsy. Kleist (8) called this form of apraxia, "innervatory apraxia". He noted that people with this form of apraxia have a loss of independent finger movements, and have problems coordinating simultaneous movements.

Lipemann (2) provided evidence that, in right handed people, ideomotor apraxia is more commonly associated with left than right hemisphere dysfunction. To learn if limb kinetic apraxia is more frequently associated with left than right hemisphere dysfunction, Heilman and colleagues (9) studied patients with epilepsy undergoing selective hemisphere anaesthesia. They found that with left hemisphere anaesthesia, right handed subjects with left hemisphere language dominance, had a loss of deftness or dexterity (limb kinetic apraxia) of both the contralateral right and the ipsilateral left hands. In contrast, with right hemisphere anaesthesia, only the contralateral left hand had a loss of deftness. Based on this study, the authors concluded that the left hemisphere of right handed people mediates motor deftness for both hands, while the right hemisphere mediates deftness for only the contralateral left hand.

The method used to assess for deftness in the Heilman et al study (9) was observing the patients while they pretended to use four different tools. The apraxic errors classified as being limb kinetic were those characterised by slowness and stiffness with …