Microstimulation of the human substantia nigra alters reinforcement learning.
Animal studies have shown that substantia nigra (SN) dopaminergic (DA) neurons strengthen action-reward associations during reinforcement learning, but their role in human learning is not known. Here, we applied microstimulation in the SN of 11 patients undergoing deep brain stimulation surgery for the treatment of Parkinson's disease as they performed a two-alternative probability learning task in which rewards were contingent on stimuli, rather than actions. Subjects demonstrated decreased learning from reward trials that were accompanied by phasic SN microstimulation compared with reward trials without stimulation. Subjects who showed large decreases in learning also showed an increased bias toward repeating actions after stimulation trials; therefore, stimulation may have decreased learning by strengthening action-reward associations rather than stimulus-reward associations. Our findings build on previous studies implicating SN DA neurons in preferentially strengthening action-reward associations during reinforcement learning.
Neuroscience Graduate Group.
Ashwin G
AG
Ramayya
Drexel University School of Biomedical Engineering, Science and Health Systems, Philadelphia, Pennsylvania 19103.
Amrit
A
Misra
Department of Neurosurgery, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19106, and baltuchg@mail.med.upenn.edu kahana@psych.upenn.edu.
Gordon H
GH
Baltuch
Department of Psychology, and baltuchg@mail.med.upenn.edu kahana@psych.upenn.edu.
Michael J
MJ
Kahana
D000368:Aged; D046690:Deep Brain Stimulation; D004558:Electric Stimulation; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010300:Parkinson Disease / Q000503:physiopathology / Q000523:psychology / Q000628:therapy*; D011337:Probability Learning; D012054:Reinforcement, Psychology; D013378:Substantia Nigra / Q000502:physiology*
Parkinson's disease; dopamine; human; microstimulation; reinforcement learning; substantia nigra