The central aim guiding our research is to understand the neural coding mechanisms in neural circuit representations of the incentive and hedonic properties of rewards. We demonstrated that neurons in the ventral pallidum encode the hedonic properties and incentive salience. We found that activation of mesolimbic circuits shifts neural coding from a mode responsive to predictive cues toward cue responses dominated by incentive motivational value. Furthermore, neural activity tracks the motivational value dynamically to follow changes in the physiological appetitive state that is relevant to reward. These findings suggest possible neural mechanisms underlying relapse in human addicts where incentive cues might trigger and “pull” individuals toward drug rewards. Currently, we are exploiting our findings on reward mechanisms to explore individual differences in the attractive power of reward cues and to translate the ideas into future clinical approaches. Some individuals are more likely to respond to and approach reward cues. Our initial findings suggest that neural responses to cues in these individuals are found in larger proportions of neurons and the activation profiles on responsive neurons are greater. We are now exploiting the sign tracking/goal tracking model to test these ideas in a Pavlovian Conditioned Approach paradigm in collaboration with colleagues in biopsychology. We believe the findings will have particular relevance in understanding why not all users of drugs become addicts. Our principal method is to record electrical activity of individual nerve cells while animals behave naturally or perform learned tasks. Experimental manipulations include: Pavlovian and instrumental training, diminished or boosted motivational drive states (e.g., diuretic salt depletion), mesolimbic activation (via sensitization and acute injections), and pharmacological stimulation (via systemic and intracranial injections of neurotransmitter agonists and antagonists).
Smith KS, Berridge KC, Aldridge JW. Disentangling pleasure from incentive salience and learning signals in brain reward circuitry. Proc Natl Acad Sci USA. 2011; 108(27), E255-264. (PMC3131314)
Patil PG, Conrad EC, Aldridge JW, Chenevert TL, Chou KL. The anatomical and electrophysiological subthalamic nucleus Visualized by 3-T magnetic resonance imaging. Neurosurgery. 2012; 71: 1089-95.
George SA, Knox D, Curtis AL, Aldridge JW, Valentino RJ, Liberzon I. Altered locus coeruleus-norepinephrine function following single prolonged stress. Eur J Neurosci. 2013, 37: 901-909
Perez-Sepulveda JA, Flagel SB, Garcia-Fuster MJ, Slusky RJ, Aldridge JW, Watson S, Akil H. Differential impact of a complex environment on positive affect in an animal model of individual differences in emotionality. Neuroscience, 2013; 248C: 436-47.
Itoga CA, Berridge KC, Aldridge JW. Ventral pallidal coding of a learned taste aversion. (submitted). 2015.
Ross SH, EL Levin, Itoga CA, Schoen CB, Selmane R, Aldridge JW. Deep brain stimulation in the central nucleus of the amygdala decreases “wanting” and “liking” of food rewards. (submitted). 2015