Retuning the misfiring brain.

Abstract

The past 20 years have witnessed enormous advances in our understanding of the structure and function of the cerebral cortex. Paramount among these advances is the realization that the detailed structural and functional organization of the cerebral cortex is maintained dynamically throughout life, shaped continually by experience and acutely by central or peripheral injury (1, 2). For example, the primary somatosensory cortex, located in the postcentral gyrus, contains an orderly ``map'' of the cutaneous receptor distribution. The various skin surfaces are represented in the cortex in a topographic fashion, with the surfaces of the feet located medially, and the hands and face more laterally. Several studies have now shown that this orderly topographic map is altered by repetitive tactile stimulation, such as takes place during the learning of a new sensorimotor skill (e.g., learning a new arpeggio on a guitar) (3–6). Cortical representations of the skin surfaces used in a skilled sensorimotor task become enlarged with practice, and cortical receptive fields become smaller. Only the representations of the most highly stimulated and trained digits are enlarged. Because somatosensory map enlargement has consistently been associated with improved behavioral performance, this dynamic process is considered adaptive. The network, cellular, and synaptic events that underlie cortical map plasticity are now beginning to be understood, as investigators in related fields, such as developmental biology, membrane biophysics, and genetic analysis, begin to address more mechanistic questions. Although it is now well accepted that training-dependent enlargements of cortical representations occur, it has also been demonstrated that unusual sensorimotor experiences can result in unusual patterns of cortical organization. For example, in a study in nonhuman primates, Clark and colleagues (7, 8) surgically connected the skin surfaces of two adjacent fingers in a so-called digital syndactly preparation. Several months later, the normal somatotopic boundary …