Brain's role in recalibration of eye-hand coordination pinpointed
A region of the brain believed to be important for maintaining the calibration
between visual and motor systems necessary for accurate eye-hand coordination
has been identified in human subjects, report researchers from Emory and
the University of California, Los Angeles, in the Oct. 16 issue of Nature.
The subjects were attempting to recalibrate their reaching to compensate
for visual displacements that resulted from viewing the world through prism
goggles. The brain region was located within a specialized area of posterior
parietal cortex (area PEG) in the hemisphere opposite the reaching hand.
"Presumably, recalibration of eye-hand coordination takes place continuously
throughout our lives, as our limbs and visual systems grow and age, and
as we learn to deal with commonplace sensory distortions such as using a
mirror to guide certain movements or adjusting to the minor spatial distortions
caused by a new pair of glasses," said senior author Garrett E. Alexander,
professor of neurology at the School of Medicine.
The process of recalibration associated with adapting to prisms was pinpointed
using positron emission tomography (PET) at the Emory PET Center to image
patterns of brain activation (reflected by changes in regional blood flow)
that occurred as subjects performed two behavioral tasks. In one task, subjects
attempted to reach to visual targets viewed through displacing prisms. In
the other, they made reaching movements identical to those of the prism
task (including error corrections caused by displacing the target while
the subject was in midreach), but there were no prisms to distort their
vision. Subtracting the second set of images from the first showed the net
effects of the recalibration (prism adaptation) process, and revealed the
selective activation of area PEG. This region of posterior parietal cortex
is known to contain both visual and somatosensory maps, making it a plausible
candidate for subserving the process of visuomotor recalibration.
Moreover, patients in whom this region has been damaged by strokes or tumors
show impairments of hand-eye coordination when they attempt to make visually
guided reaches with the opposite hand.
Alexander's collaborators include Dottie M. Clower, graduate student in
Emory's neurosciences program and Department of Neurology; John M. Hoffman,
associate professor, neurology and radiology departments at Emory; John
R. Votaw, assistant professor, and Tracy L. Faber, assistant professor,
Department of Radiology at Emory; and Roger P. Woods, assistant professor,
Division of Brain Mapping, UCLA School of Medicine.
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