Effects of Amygdala Inactivation on Affective Processing by the Nucleus Accumbens

Inappropriate affect is a major feature of many psychological disorders. Recent progress in the field of affective neuroscience has led to a basic understanding of the brain regions involved in emotional processing. However, this information remains incomplete as we have yet to directly link affective stimuli with the specific patterns of brain activity they evoke. Such information can fuel better-targeted therapies in the treatment of affective disorders. Recent studies have shown that the nucleus accumbens (NAc) differentially responds to stimuli based on their affective valence and is thought to translate affective signals into behavioral responses. This dissertation sought to understand which areas of the central nervous system prove critical for appropriate affective encoding by the NAc. One candidate source is the basolateral amygdala (BLA) - an important emotional processing center which communicates directly with the NAc. Here, I temporarily inactivated the BLA while monitoring activity in the NAc to determine the contribution of the BLA to affective processing by the NAc. Results showed that under BLA inactivation the NAc no longer differentiated between the rewarding taste of sucrose and the aversive taste of quinine. This was due to a selective change in the way the NAc responded to sucrose. Furthermore, under BLA inactivation rats increased the number of rejection responses emitted to sucrose, suggesting that sucrose had lost some of its palatability. This study illustrates a functional link between the amygdala and the NAc in differentiating reward and aversion and highlights the importance of differential NAc encoding for appropriate behavioral responses to affective stimuli.