Disentangling the P300 Components of Evoked Potentials Elicited using Subliminal Oddball Tasks in Reward-Directed Motivation

Objective: The objective of this study was to investigate neural responses during subliminal oddball tasks concerning reward-directed motivation to distinguish the P3a and P3b components of evoked P300 potentials. Methods: The subliminal oddball task included congruent/incongruent stimuli and masked prime subliminal stimuli. The task was to push the button when an incongruent stimulus appeared. Participants underwent two pre- and post-break electroencephalogram (EEG) recordings. During the break, the thirst scores of the participants were evaluated. Then, participants consumed three different salty foods in the same amount and completed the remaining two post-break EEG recordings, followed by the second thirst scores evaluation. Finally, participants physically selected lettered cards (A, B, C, and D) to receive a reward and quench their thirst. Results: Thirty participants were enrolled, 28 of whom were included for data analysis. Ten participants selected lettered cards as the given subliminal stimulus (sub (+) group), and 18 participants selected different lettered cards from the given subliminal stimulus (sub (-) group). We found a significant increase in post-P3a and post-P3b amplitudes in the sub (+) group at the Pz/Oz electrodes. Changes in P3b amplitude were significantly higher in the sub (+) group (2.83 ± 1.14 μV) than in the sub (-) group (0.62 ± 2.29 μV) at the Pz/Oz electrodes. Correlation analysis revealed that higher thirst scores resulted in higher P3b amplitudes in the sub (+) group. Conclusion: These findings suggest that reward-directed motivation increases parietal-posterior P3b amplitudes, signifying the involvement of cognitive processes to achieve a reward.