Learning-induced Plasticity In The Sensory Systems

The adult brain shows remarkable plasticity, learning-induced plasticity is that an awake animal learns the association between two events and modifies processing ability of its brian to specific information and thus change its behavior as a function of the learned association. Across sensory modalities, the re-tuning of neurons to a significant stimulus or map reorganizations in favor of the significant stimuli were observed at the thalamic and/or cortical level. The analysis of the literature in each sensory modality indicates that relationships between learning-induced sensory plasticity and behavioral performance can, or cannot, be found depending on the tasks that were used.Receptive field (RF) plasticity, 2DG and map changes obtained in the auditory and somatosensory system are reviewed. In the visual system, as there is no RF and map analysis during learning per se, the evidence presented are from increased neuronal responsiveness, and from the effects of perceptual learning in human and non human primates. Practising visual signal discrimination can change neural plasticity in the visual pathway, the mechanism of which remains unknown.In the present experiment, two adult cats were trained to discriminate respectively the horizontal and vertical static sinusoidal gratings for food reward. Performance of the two cats improved significantly with the extension of training, all reaching a percent correct above 85% after 4 months. Testing with an orientation orthogonal to the trained orientation showed that correct performance of the two cats decreased obviously. Extracellular recording the responses of dLGN neurons to sinusoidal gratings with different orientations revealed that, compared with that in untrained cat, preferred orientations of dLGN neurons in trained cats did not shift in favor of the trained orientation. However, for cells whose receptive fields located at the position of 10°-15° visual acute away from the fovals, trained cats showed distinguished increase in orientation selectivity and significant decrease in spike counts at trained orientation compared with that in untrained cat. The result above indicates that orientation discrimination practising can leads to specific shift of orientation sensitivity for at least part of the dLGN neurons, which may contribute to the neural plasticity of orientation coding in visual cortex.