Drug addiction involves an excessive motivation to pursue and consume drugs. Part of this motivation is thought to involve the attribution of value to drug-paired cues. Cues for rewards, including drugs and food, can become motivational targets and attract attention and behavior. In the brain, a basic sketch of areas responsible for this process is known and includes the nucleus accumbens (NAc) and ventral pallidum (VP). Although these areas are bidirectionally connected as a circuit, little is known about how motivation arises out of their circuit dynamics. To address this, the proposed research will incorporate a method called chemogenetics for relatively non-invasive ?remote control? perturbation of brain activity. Combining this method with transgenic delivery strategies, we will both increase and decrease activity in pathways connecting the NAc and VP to evaluate their role in the motivational attraction to reward cues. This motivational process is exemplified by sign-tracking behavior, in which animals appetitively engage with a cue predicting reward. In the proposed research, connections between the NAc and VP will be manipulated using DREADDs to assess the role of these pathways in acquiring and expressing the sign-tracking behavior. Recordings of neural activity and gene expression assays will complement these experiments in order to establish neural activation patterns that change in register with changes in motivated behavior. We will similarly test the role of neurons in the VP expressing acetylcholine, which receive NAc input and are hypothesized to guide attention towards reward cues. Results showing how NA-VP circuits control motivation, and what neural activity signatures map on to increases and decreases in motivation, will provide critical reference points for an understanding of how pathway-specific changes in brain activity could contribute to excessive motivation in addictive behaviors. The relative non-invasiveness of the procedure also carries translational potential for disrupting severely excessive reactions to drug-associated stimuli.
A core symptom in addiction is an excessive motivational reaction to environmental cues that have been associated with drug use. The proposed research will use state-of-the-art technologies to characterize brain mechanism by which such motivational value is added to environmental cues for rewards. Experiments will resolve long-standing questions about how the ?reward network? of the brain functions as a circuit to control normal and excessive motivation.
