Journal of Neuroscience, Vol 14, 2515-2530, Copyright © 1994 by Society for Neuroscience
Role of the forebrain commissures in bihemispheric mnemonic integration in macaques
JD Lewine, RW Doty, RS Astur and SL Provencal
Department of Physiology, University of Rochester School of Medicine and Dentistry, New York 14642.
A serial probe recognition task was used to examine the interhemispheric
exchange of visual data in macaques. Each block of trials began with the
memorization of one to six visual target images. The monkeys then had to
determine, in tests that followed immediately, whether probe images were or
were not members of the learned target set. Previous work with both humans
and macaques has shown that the time required for the evaluation of probes
generally increases, while response accuracy decreases, as a function of
the number of targets, the "memory load". By testing animals with bisected
optic chiasm, it was possible to direct visual information to only one
hemisphere at a time, simply by occluding the opposite eye. In this
fashion, the quality of intrahemispheric evaluations (in which a monocular
probe was a match for a target previously viewed through the same eye) was
compared with that of interhemispheric evaluations (in which a probe was a
match for a target previously designated through the opposite eye). A key
question was whether division of the target list between the hemispheres
modified the relationships between reaction time, response accuracy, and
memory load. Provided that either the anterior commissure or the splenium
of the corpus callosum was intact, interhemispheric processing was only
subtly less efficient than intrahemispheric processing. The ability to
perform interhemispheric evaluations was selectively and completely
disrupted if all forebrain commissural fibers were transected. In this
latter split-brain condition, the time required for probe evaluations was,
as expected, determined solely by the number of target items memorized by
the probed hemisphere. Accuracy, however, was always a function of the
total memory load, regardless of the distribution of targets between the
hemispheres. This implies, first, that accuracy and latency do not reflect
identical mnemonic factors, as frequently held, and second, that in
mnemonic processing, the two hemispheres draw upon a unified, shared
resource, probably allocated by the intact brainstem.
.gif?ad=17923&adview=true)
Memory
Previous Article | Next Article
