A Neural Correlate of Reward-Based Behavioral Learning in Caudate Nucleus: A Functional Magnetic Resonance Imaging Study of a Stochastic Decision Task

TLDR

Humans learn reward‑maximizing behaviors through trial‑and‑error, and neural activity in the midbrain and ventral striatum signals reward‑prediction errors. The study aims to determine whether the striatum, particularly the caudate nucleus, is the primary locus of reward‑based behavioral learning. Participants performed a stochastic monetary‑reward decision task while undergoing fMRI, and the authors correlated brain activity with behavior‑derived explanatory variables. Caudate nucleus activity tracked short‑term reward and matched the magnitude of behavioral change during learning, a relationship that persisted across varying task difficulties, indicating the caudate as a key locus of reward‑based behavioral learning.

Abstract

Humans can acquire appropriate behaviors that maximize rewards on a trial-and-error basis. Recent electrophysiological and imaging studies have demonstrated that neural activity in the midbrain and ventral striatum encodes the error of reward prediction. However, it is yet to be examined whether the striatum is the main locus of reward-based behavioral learning. To address this, we conducted functional magnetic resonance imaging (fMRI) of a stochastic decision task involving monetary rewards, in which subjects had to learn behaviors involving different task difficulties that were controlled by probability. We performed a correlation analysis of fMRI data by using the explanatory variables derived from subject behaviors. We found that activity in the caudate nucleus was correlated with short-term reward and, furthermore, paralleled the magnitude of a subject's behavioral change during learning. In addition, we confirmed that this parallelism between learning and activity in the caudate nucleus is robustly maintained even when we vary task difficulty by controlling the probability. These findings suggest that the caudate nucleus is one of the main loci for reward-based behavioral learning.