Introduction: The ability to make predictions about the environment is critical for an organism’s survival, and the reward system in mammals is critical to this ability. Various reward centers have been shown to project to the subthalamic nucleus (STN) (1), and recent evidence in animal models suggests that the region is involved with reward expectation (2,3). Our experiments extend these results and specifically test for reward expectation in the human STN.
Methods: Parkinson’s Disease patients (n=9) were asked to participate in our study during microelectrode recording as part of the deep brain stimulation (DBS) procedure. Within confirmed ventral STN, patients were presented with a visual stimulus (a green dot), followed one second later by either a reward (several drops of sugar water/32 trials) or nothing (6 trials). The reward/non-reward conditions were analyzed and compared using spike rates, LFP data, and the RMS summary statistic using MATLAB.
Results: LFP analysis has shown an unsurprising heterogeneous response. Multiple recordings demonstrate population activity correlated with the stimulus, the reward, or both in the Alpha and Beta bands (see Fig 1A for example). Other STN neurons appear to encode for prediction error in the same bands; i.e., the neurons respond when they receive an unexpected reward, or do not receive an expected reward4 (see Fig 1B for example).
Conclusions: The preliminary results are in line with previous non-human research - the STN is appears to be related to reward expectation, with some sites showing activity when that expectation is violated. Further study is being done to link these results to the reward system as a whole, and the STN's place in it.
Patient Care: If it is proven that the STN is involved in reward expectation, perhaps this can be utilized as an advantage in future STN-DBS applications in different neurocognitive pathologies beyond that of Parkinson's disease.
Learning Objectives: By the conclusion of this poster session, participants should be able to 1) Understand the literature suggesting the STN’s role in the mammalian reward system, 2) Understand the concept of reward expectation and prediction error response, and 3) Identify the STN as a potential physiological basis for reward expectation in humans.
References: 1. Haegelen, C., Rouaud, T., Darnault, P. & Morandi, X. The subthalamic nucleus is a key-structure of limbic basal ganglia functions. Med. Hypotheses 72, 421–426 (2009).
2. Darbaky, Y., Baunez, C., Arecchi, P., Legallet, E. & Apicella, P. Reward-related neuronal activity in the subthalamic nucleus of the monkey. Neuroreport 16, 1241–1244 (2005).
3. Lardeux, S., Paleressompoulle, D., Pernaud, R., Cador, M. & Baunez, C. Different populations of subthalamic neurons encode cocaine vs. sucrose reward and predict future error. J. Neurophysiol. 110, 1497–1510 (2013).
4. Schultz, W. Neuronal Reward and Decision Signals: From Theories to Data. Physiol. Rev. 95, 853–951 (2015).