Yusuke Nakashima¹, Yuka Sasaki¹, Takeo Watanabe¹; ¹Brown University

Reward and arousal, two major neuromodulatory signals in the brain, significantly influence various types of visual functions. The previously believed distinctions between reward and arousal have become less clear. Here, by manipulating the reward and sound levels, for the first time, we demonstrate that the effects of reward and arousal can be dissociated using EEG alpha power. To manipulate reward levels, participants in the higher-value group were deprived of food and water for four hours prior to the experiment, while those in the lower-value group were not. In each trial, a drop of water was given to both groups. To manipulate arousal levels, a clicking sound was either presented or omitted. All participants underwent the following three conditions: (1) in the reward condition, water was provided. (2) in the arousal condition, a sound was presented, (3) in the reward+arousal condition, both water and sound were presented. During each trial, participants passively viewed a dynamic sequence of Mondrian patterns for 15 seconds, while pupil size and EEG alpha power in response to water and/or sound were recorded. Across all three conditions, pupil size increased similarly in both the lower- and higher-value groups, suggesting that pupillary responses do not reflect reward value. In contrast, EEG alpha power exhibited distinct patterns: in the higher-value group, alpha power significantly decreased from the pre-stimulus baseline in the arousal condition but increased in the reward condition. Conversely, in the lower-value group, alpha power decreased in both the arousal and reward conditions. Our findings indicate that alpha power effectively dissociates the effects of reward (water) and arousal (sound). Additionally, our results suggest that water induces not only a reward effect, reflected in increased alpha power, but also an arousal effect, reflected in pupil dilation and decreased alpha power.

Acknowledgements: NIH R01EY019466, R01EY027841, R01EY031705, NSF-BSF BCS2241417