Subthalamic nucleus stimulation reverses human decision-making biases

Effective decision-making requires the ability to override impulsive reactions, especially when choosing between multiple high-value options. The medial prefrontal cortex (mPFC) is known to monitor conflict, but the precise mechanism by which this monitoring leads to behavioral control has remained debated. This paper investigates the role of the subthalamic nucleus (STN) in this process, proposing that it acts as a 'brake' on the cortico-striatal system, allowing for deliberation during difficult choices.

Using electroencephalography (EEG), the researchers identified that increased theta-band power (4–8 Hz) in the mPFC predicts a slowing of response times when individuals face high-conflict decisions. Through the application of the drift diffusion model (DDM), they demonstrated that this mPFC theta activity correlates with a higher decision threshold—a latent variable representing the amount of evidence required before an action is selected. In essence, the mPFC signals the need for caution, which the STN translates into a slower, more deliberate response process.

Deep brain stimulation (DBS) is a common treatment for Parkinson's disease, but it is known to sometimes induce impulsivity. By comparing patients with their stimulators ON versus OFF, the researchers found that DBS disrupts the normal coupling between mPFC theta power and decision threshold. When the stimulator is active, the natural adjustment that typically increases the decision threshold in response to conflict is abolished or even reversed, resulting in faster, premature responses during high-conflict situations.

To further validate these findings, the study included direct intracranial recordings from the STN area in patients undergoing surgery. These recordings revealed enhanced low-frequency activity (2.5–5 Hz) during high-conflict trials, closely paralleling the dynamics observed in the mPFC. This provides strong evidence that the STN is a critical node in a neural network that regulates behavior, and that high-frequency DBS interferes with the endogenous low-frequency signaling essential for implementing controlled, deliberative decision-making.