Human Substantia Nigra Neurons Encode Unexpected Financial Rewards
Kareem A. Zaghloul,1*
Justin A. Blanco,2
Christoph T. Weidemann,3
Kathryn McGill,1
Jurg L. Jaggi,1
Gordon H. Baltuch,1
Michael J. Kahana3*
The brain's sensitivity to unexpected outcomes plays a fundamental
role in an organism's ability to adapt and learn new behaviors.
Emerging research suggests that midbrain dopaminergic neurons
encode these unexpected outcomes. We used microelectrode recordings
during deep brain stimulation surgery to study neuronal activity
in the human substantia nigra (SN) while patients with Parkinson's
disease engaged in a probabilistic learning task motivated by
virtual financial rewards. Based on a model of the participants'
expected reward, we divided trial outcomes into expected and
unexpected gains and losses. SN neurons exhibited significantly
higher firing rates after unexpected gains than unexpected losses.
No such differences were observed after expected gains and losses.
This result provides critical support for the hypothesized role
of the SN in human reinforcement learning.
2 Department of Bioengineering, University of Pennsylvania, Philadelphia, PA 19104, USA.
3 Department of Psychology, University of Pennsylvania, Philadelphia, PA 19104, USA.
* To whom correspondence should be addressed. E-mail: zaghlouk{at}uphs.upenn.edu (K.A.Z.); kahana{at}psych.upenn.edu (M.J.K.)
