Hemispheric asymmetries in motor function: II. Ordering does not contribute to left-hemisphere specialization

Area of Science:

• Neuroscience
• Cognitive Psychology
• Neurology

Background:

• The specialization of brain hemispheres for specific cognitive functions is a key area of neuroscience research.
• The role of the left hemisphere in motor control, particularly in the sequencing of actions, has been debated.

Purpose of the Study:

• To investigate whether the left hemisphere is specialized for the ordering of motor acts.
• To differentiate between the generation of motor acts and their subsequent ordering and execution.

Main Methods:

• Patients with unilateral brain lesions (left or right vascular origin) were tested on motor tasks.
• Tasks included manual sequence learning and speeded performance tests with varying ordering demands.
• Detailed analysis of Ideational Apraxia task performance was conducted.

Main Results:

• Patients with left- and right-sided lesions showed similar responses to altered ordering demands in motor tasks.
• Left-sided lesion patients' deficits on the Ideational Apraxia task were characterized as impaired act generation, not ordering.
• No evidence supported left-hemisphere specialization for the ordering of motor acts.

Conclusions:

• The findings do not support the hypothesis of left-hemisphere specialization for ordering motor acts.
• A two-stage model of motor function is proposed: left-hemisphere lateralized generation of motor 'target' acts, and non-lateralized ordering and execution of these acts.