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Abstract:
Anterior frontal lesions in man produce few movement control
problems, a fact which has complicated functional characterization
of these cortical regions. Because, frontal lesions cause problems
in antisaccades, it was hypothesized that they should also impair
inverted arm movements such as mirror movements. We tested this
idea in 9 patients with a unilateral frontal excision (dorsal
premotor and prefrontal) matched to 9 patients with temporal
excisions and 9 controls. Subjects moved a stylus on a graphics
tablet from the center to a peripheral target while indirectly
monitoring their movements on a monitor. In a baseline condition,
movements were straight and fast in all groups. In a condition of
full inversion with no transformation of the axis of movement,
frontals showed a stronger tendency than others to initiate
movements in the natural direction. In a more difficult condition
of reflection of a single axis (mirror inversion), frontals showed
the same initiation problem but also showed problems in executing
movement corrections during the initial adaptation. Finally, the
three groups did not differ in their overall rate of adaptation to
the space transformations as measured by the precision of
execution. These results indicate that frontal lesions produce
planning and execution deficits in inverted movements and suggest
that anterior frontal cortex is essential for the on-line
attentional control of unlearned movements but not for programmed
control of learned movements.
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