Introduction

How do individual cortical areas come to process unique kinds of information and contribute to particular behaviors? This question lies at the heart of understanding how the cortex develops and acquires its functional capacities, yet there have been few direct approaches to answering it. In particular, it has proved difficult with the classical models of cortical development to separate intrinsic aspects of developmental programs from those that are influenced by extrinsic factors. A different paradigm for examining the question comes from cross-modal plasticity. Such plasticity, induced by rewiring the brain early in life, utilizes the inputs of one modality to drive cortical areas that normally process information from a different modality. These experiments provide important evidence that several aspects of cortical development and function are crucially influenced by the nature of input activity. This chapter reviews the logic of rewiring experiments in which visual inputs are induced to drive the auditory cortex, the physiological and behavioral consequences of rewiring, and the implications of these findings for mechanisms by which cortical areas acquire unique identities and processing functions or are able to carry out multisensory integration.