Behavioral adaption is crucial for an organism to survive in a living environment. Among the various forms of behavioral adaptation, associative learning has received long time attention and research devotion. The essence of associative learning is the gain of significance for otherwise insignificant stimuli (CS) from pairing experiences with biologically meaningful stimuli (US). Empirical studies performed in this dissertation have utilized two types of associative learning, taste aversion conditioning (CTA) and Pavlovian appetitive conditioning. Using a single-unit recording technique, efforts have been attempted to investigate the neuronal adaptation occurring in the basolateral nucleus of the amygdala (BLA) and the midbrain dopaminergic neurons as a consequence of learning.

The first two chapters in this dissertation are dedicated to provide research rationale for the perspective that BLA might be the locus of association between taste and illness. An experiment describes the consequence of CTA learning in encoding the taste stimulus in BLA.

In the central nervous system, the neuromodulators play crucial roles in the formation of association. The neuromodulatory transmitters secreted by a small group of neurons diffuse through large areas of the nervous system. Understanding the adaptation occurring in the neuromodulatory system through learning might provide new insights into comprehending the complex dynamics underlying the learning processes in the nervous system. The function of dopamine (DA) has received considerable attention among the various neuromodulatory systems.

The rest of the chapters of this dissertation focus on the organization of the DA system, the signal cascade elicited by DA transmission, electrophysiological properties of DAergic neurons, and several popular DA hypotheses including the prediction error. The empirical studies describe the alteration of encoding taste and auditory stimuli in midbrain DAergic neurons due to CTA learning and Pavlovian appetitive conditioning.