The Journal of Neuroscience, February 1, 2001, 21(3):1056-1061
The Topography of Tactile Learning in Humans
Justin A.
Harris,
Irina M.
Harris, and
Mathew E.
Diamond
Cognitive Neuroscience Sector, International School for Advanced
Studies (SISSA), 34014 Trieste, Italy
The spatial distribution of learned information within a sensory
system can shed light on the brain mechanisms of sensory-perceptual learning. It has been argued that tactile memories are stored within a
somatotopic framework in monkeys and rats but within a widely
distributed network in humans. We have performed experiments to
reexamine the spread of tactile learning across the fingertips. In all
experiments, subjects were trained to use one fingertip to discriminate
between two stimuli. Experiment 1 required identification of vibration
frequency, experiment 2 punctate pressure, and experiment 3 surface roughness. After learning to identify the stimuli reliably, 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. As expected, for all stimulus types, subjects showed
retention of learning with the trained fingertip. However, the transfer
beyond the trained fingertip varied according to the stimulus type. For
vibration, learning did not transfer to other fingertips. For both
pressure and roughness stimuli, there was limited transfer, dictated by
topographic distance; subjects performed well with the first neighbor
of the trained finger and with the finger symmetrically opposite the
trained one. 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.
Key words:
somatosensory; cortex; vibration discrimination; von
Frey; roughness discrimination; plasticity
Copyright © 2001 Society for Neuroscience 0270-6474/01/2131056-06$05.00/0
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