343 Neuroplastic Adaptations of the Auditory System in Musicians and Nonmusicians LARRY E. ROBERTS*, DANIEL J. BOSNYAK*, ANTOINE SHAHIN # , and LAUREL J. TRAINOR* *Department of Psychology; and # Unit for Medical Physics and Applied Radiation Sciences, McMaster University, Hamilton, Ontario, Canada 1. INTRODUCTION The human ear has been adapted by evolutionary processes to respond to sound frequencies that are present in the environment and convey information relevant to survival and reproductive fitness. However, the specific features of most sounds that we hear on a second-by-second basis (for example, the harmonic structure, loudness, and temporal shape of a particular voice, language, or musical note) and the meaning attached to these sounds are unique for each individual and cannot be anticipated by a genetic code. The evolutionary response to this limitation on natural selection has been the development of mechanisms that represent the detailed features of sensory input (sensory maps) and update those representations on a millisecond time scale (neural plasticity). We describe two experiments which used auditory evoked potentials (AEPs) to study these processes in the human brain. 2. EXPERIMENT 1 Alteration of the tuning properties of auditory neurons by aversive conditioning in the adult guinea pig has been documented in primary (A1) and secondary (A2) auditory cortex as well as in the medial, dorsal, and ventral divisions of the auditory thalamus (Edeline 1999). When brain