The goal of the described experiments was to document the effects of long-term and short-term experience with sounds that change in frequency on primary auditory cortex (A1). Previous studies by our laboratory have elaborated the relationship between acoustic experience and network plasticity demonstrating that (1) spectral variability and modulation rate of experienced sounds determine frequency selectivity of cortical neurons (2) the size of sensory area stimulated determine map reorganization and that (3) all these changes are influenced by background conditions. We have employed a well-established paradigm that uses stimulation of nucleus basalis (NB) paired with presentation of simple and modulated sounds to systematically reveal the effect of manipulating acoustic experience on cortical plasticity (Kilgard et al. 2001b). My experiments extend these results by pairing NB stimulation with spectro-temporally complex sounds such as FM sweeps in different conditions varying the pattern of activation and the acoustic background. In addition I evaluated how changes in receptive field structure and temporal fidelity can arise from short-term experience with these sounds based on a spike-timing dependent plasticity model. In summary this thesis documents for the first time (1) how FM sweeps of one octave width are represented along three relay centers of the auditory pathway: Thalamus, A1, PAF, (2) how experience with FM sweeps changes the representation of these sounds and A1 properties (i) long-term (over ∼20 days) and (ii) short-term (within minutes) and (3) how details of experience influence cortical plasticity with regard to (i) the extent of the sensory area activated by a stimulus and (ii) the background conditions in which a stimulus is presented. These results will be essential in understanding cortical processing of complex stimuli, complex activation patterns and processing of sound in complex acoustic environments, and will lay the ground for a new approach of experimental design in sensory systems.