Citation/Abstract

Humans and many other species have the capacity to learn and change their behavioral responses when they repeatedly practice a discrimination task. This change in behavior must be caused by changes in response properties of the nervous system. Understanding the relationship between learning and changes in neural responses has been an important field of study for the past twenty years. Numerous papers have observed correlations between plasticity in primary cortical areas and improved perceptual discrimination abilities, implying that this plasticity is the underlying cause of improved performance. However, a causal relationship cannot be proven unless plasticity is induced outside of a behavioral context. In the following dissertation I document the perceptual consequences of plasticity induced using stimulation of the nucleus basalis paired with auditory stimuli. The nucleus basalis is a deep-brain structure which releases acetylcholine onto the neocortex during behaviorally important events. Damage to this structure has been shown to impair both learning and plasticity, and stimulation during presentation of sensory stimuli produces plasticity which mimics the effects observed after behavioral training. We demonstrate for the first time that pairing nucleus basailis stimulation with a tone can alter learning and performance of a frequency discrimination task. We also document a pattern of plasticity after discrimination training and nucleus basalis stimulation which indicates that cortical plasticity in primary sensory areas may be important for learning but not performance of a discrimination task. Finally, we report a further possible source of cortical plasticity and behavioral improvement by showing that nucleus basalis-stimulation pairing can cause stimulus-specific plasticity in both primary and secondary cortical areas. The results of these studies reveal that cortical plasticity contributes to sensory discrimination and perceptual learning, and provide new insights about the relationship between cortical plasticity and continued performance of well-learned behavioral tasks.