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Abstract:
The spatial distribution of learned information within a
sensory system can shed light on the brain mechanisms of
sensory-perceptual learning. Evidence from monkeys and rats
suggests that tactile memories are stored within a somatotopic
framework, but studies in humans point to a widely-distributed
non-topographic network for tactile learning. We conducted
experiments reexamining the spread of tactile learning across
fingertips. Subjects were trained to use one fingertip to
discriminate between different vibration frequencies, different
punctate pressures, or different surface roughnesses. After
learning, subjects were tested with the trained fingertip, its
first and second neighbors on the same hand, and the three
corresponding fingertips on the opposite hand. For all stimuli
subjects showed retention of learning with the trained fingertip.
However, transfer beyond the trained finger varied according to the
stimulus type. For vibration, learning did not transfer to other
fingertips. For both pressure and roughness, there was limited
transfer dictated by topographic distance: subjects performed well
with both the first neighbor and the finger symmetrically opposite
the trained finger. These results indicate that tactile learning is
organized within a somatotopic framework, reconciling the findings
in humans with those in other species. The differential
distribution of tactile memory according to stimulus type suggests
that the information is stored in stimulus-specific somatosensory
cortical fields, each characterized by a unique receptive field
organization, feature selectivity, and callosal
connectivity.
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