Sensitivity of frontal beta oscillations to reward valence but not probability.

Reward feedback elicits a brief increase in power in the high-beta frequency range of the human electroencephalogram (EEG) over frontal areas of the scalp, but the functional role of this oscillatory activity remains unclear. An observed sensitivity to reward expectation (HajiHosseini, Rodríguez-Fornells, and Marco-Pallarés, 2012; [2]) suggests that reward-related beta may index a reward prediction error (RPE) signal for reinforcement learning. To investigate this possibility we reanalyzed EEG data from two prior experiments that revealed RPEs in the human event-related brain potential (Holroyd and Krigolson, 2007 [12]; Holroydet al., 2008 [13]). We found that feedback stimuli that indicated reward, when compared to feedback stimuli that indicated no-reward, elicited relatively more beta power (20-30 Hz) over a frontal area of the scalp. However, beta power was not sensitive to feedback probability. These results indicate that reward-related beta does not index an RPE but rather relates to a different reward processing function.