Opposite polarities in alpha-band power in EEG were induced by reward and arousal: an initial discovery in the psychophysiological realm that distinctly dissociates reward from arousal

Neuromodulatory signals, such as reward and arousal, significantly influence perceptual processing (Seitz et al., 2009; Vinck et al., 2015). While reward and arousal are mediated by distinct neural mechanisms, their psychophysiological responses, like pupil dilation, often exhibit such similarity that discerning between them becomes challenging (Aston-Jones & Cohen, 2005; Bijleveld et al., 2009). In our study, we observed clear differences in alpha-band power in EEG recordings. We conducted experiments measuring pupillary responses and alpha power in EEG following presentations of reward and sound. Each participant underwent a four-hour fasting period before engaging in three conditions. In the reward condition, a drop of water was provided via a tube. In the sound condition, a clicking sound was presented to increase arousal levels. The reward+sound condition involved simultaneous presentation of both water and sound. During each condition, while participants passively viewed a dynamic sequence of Mondrian patterns for a total of 15 sec, water and/or sound was presented 1 to 4 times. Our findings showed a significant increase in pupil size in all three conditions, suggesting that reward and arousal have similar effects on pupillary responses. The alpha power in the occipital region significantly decreased from the pre-stimulus baseline in the sound condition. Conversely, alpha power increased in the reward and reward+sound conditions. These results indicate that alpha power can effectively differentiate between the effects of reward and arousal. Given that decreased alpha power is associated with excitation including arousal, it is plausible that increased alpha power could be involved in inhibition linked to reward.