Rewiring Cortex: Functional Plasticity of the Auditory Cortex during Development

1. INTRODUCTION How does the primary auditory cortex (A1) derive its function? Is it primarily determined by intrinsic factors expressed within cortex (i.e. molecular gradients, patterns of gene expression) or extrinsic factors that originate outside cortex (i.e. sensory experience)? This is a pivotal issue for understanding the development and function of A1, yet one that is difficult to address using traditional experimental methods because these techniques are unable to separate out the relative contributions of intrinsic and extrinsic factors. However, cross-modal experiments where the inputs of one sensory modality are redirected to a different modality, in effect " rewiring " the brain, are able to distinguish the two and provide insight. Rewiring experiments also reveal how input activity modifies cortical organization as well as the limitations imposed on this plasticity by the underlying cortical substrate. In this chapter we review rewiring experiments in which visual inputs are induced to innervate the auditory pathway, and describe its physiological and behavioral consequences as well as the implications for normal cortical processing and human cross-modal plasticity.