Environmental and training-induced plasticity in primary auditory cortex

Previous studies have demonstrated that a rich, stimulating environment results in both anatomic and physiologic changes in the cerebral cortex. In addition to generalized sensory experience, training on perceptual learning tasks also alters neurophysiologic responses in sensory and motor cortex. The effects of both enrichment and training on responses from auditory cortex neurons are examined in this dissertation. Although there is a vast literature spanning almost three decades on the anatomic and morphologic effects of enrichment, comparatively fewer studies have focused on the neurophysiologic consequences of enrichment. For example, neurophysiologic effects of enrichment have been demonstrated in visual (Beaulieu and Cynader 1990a, b) and somatosensory (Coq and Xerri 1998) cortex. In these studies, enrichment sharpened orientation tuning in visual cortex and increased the area of forepaw representation in somatosensory cortex. The effects of enrichment on the processing of auditory cortex neurons are not known. In the first part of my dissertation, the effects of enrichment on the auditory cortex are documented. Changes in spectral and temporal responses from primary auditory cortex (A1) neurons of enriched rats were compared to responses from rats in standard conditions using multi-unit recordings. Enrichment dramatically enhanced cortical responses across A1, increased frequency selectivity and sensitivity and altered temporal processing without affecting cortical map reorganization (Engineer et al. 2004). The next study was designed to document the effects of auditory discrimination training on responses from auditory cortex neurons. Both animals and humans get better at discrimination tasks with practice. More recently, these studies have been combined with electrophysiological recordings (unit recording, evoked potentials, fMRI) to probe task specific effects on cortical responses. The second part of this dissertation documents the neurophysiologic consequences of auditory sequence learning on rat A1 neurons.; The results of these and earlier studies indicate that exposure to a rich, stimulating environments or training on perceptual learning tasks can significantly alter sensory information processing of cortical neurons. Although the exact consequences of plasticity on cortical development or recovery from injury are not clear, numerous studies suggest that environmental enrichment and/or behavioral training may be useful remediation strategies in promoting recovery from neurological disability.