Good Vibrations: Cross-frequency Coupling in the Human Nucleus Accumbens during Reward Processing

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Abstract
The nucleus accumbens is critical for reward-guided learning and decision-making. It is thought to "gate" the flow of a diverse range of information (e.g., rewarding, aversive, and novel events) from limbic afferents to basal ganglia outputs. Gating and information encoding may be achieved via cross-frequency coupling, in which bursts of high-frequency activity occur preferentially during specific phases of slower oscillations. We examined whether the human nucleus accumbens engages such a mechanism by recording electrophysiological activity directly from the accumbens of human patients undergoing deep brain stimulation surgery. Oscillatory activity in the gamma (40-80 Hz) frequency range was synchronized with the phase of simultaneous alpha (8-12 Hz) waves. Further, losing and winning small amounts of money elicited relatively increased gamma oscillation power prior to and following alpha troughs, respectively. Gamma-alpha synchronization may reflect an electrophysiological gating mechanism in the human nucleus accumbens, and the phase differences in gamma-alpha coupling may reflect a reward information coding scheme similar to phase coding.