Tactile Learning In A Topographic Framework

Having briefly argued that somatosensory cortex is a key component of the total neuronal ensemble that gives rise to the online experience, recall, and expectation of tactile events, we turn to the second issue: what is the role of somatosensory cortical topography in perceptual learning? One way of investigating the role of cortical topography is to require subjects to learn a task using a restricted set of sensory receptors. Later, they are tested on the same task, but are required to use a different set of receptors in the same sensory system. If the learning process is widely distributed, showing no respect for topographic boundaries, or if the learned information resides in "higher" areas, whose organization does not conserve the topographic arrangement of the sensory apparatus, then subjects will be able to transfer learning immediately to a second set of sensory receptors, regardless of the relative positions of the "trained" and "tested" sensory receptors. In contrast, if the learning process preferentially involves one part of the cortical topographic field, then learning transfer will be incomplete: subjects will require some retraining time before accomplishing the task using the second set of sensory receptors (Figure 7.2). This strategy has been applied to examine the distribution of learning in the visual

FIGURE 7.2 Schematic diagram illustrating two alternative models for the cortical distribution of sensory learning. On the left, an orderly array of sensory receptors projects to an orderly array of cortical processing zones, which correspond to storage sites for learned information. On the right, the cortical processing and storage zones are widely distributed, highly overlapping, and do not conserve topographic order. Experiments that probe the patterns of learning transfer to nearby sensory receptors after training with one restricted site can discriminate between these models.

FIGURE 7.2 Schematic diagram illustrating two alternative models for the cortical distribution of sensory learning. On the left, an orderly array of sensory receptors projects to an orderly array of cortical processing zones, which correspond to storage sites for learned information. On the right, the cortical processing and storage zones are widely distributed, highly overlapping, and do not conserve topographic order. Experiments that probe the patterns of learning transfer to nearby sensory receptors after training with one restricted site can discriminate between these models.

modality23-25 and we have used the same strategy to uncover the distribution of learning in the tactile modality.26-29 Our experiments, reviewed below, show that when animals or human subjects learn a tactile discrimination task, the neural modifications associated with the learning are distributed according to the spatial arrangement of the cortical map.

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