Roach, B. J. | bioRxiv Science

bioRxiv2020

Electrophysiological investigation of reward anticipation and outcome evaluation during slot machine play

Slot machines are a popular form of gambling, offering a tractable way to experimentally model reward processes. This study used a 3-reel slot paradigm to assess psychologically distinct phases of reward processing, reflecting anticipation, and early and late-stage outcome processing. EEG measures of winning, nearly missing (a losing outcome revealed at the final, third reel), and "totally" missing (a losing outcome revealed earlier, at the second reel) were collected from healthy adults (n=54). Condition effects were evaluated in: i) event-related potential (ERP) components reflecting anticipatory attention (stimulus preceding negativity, SPN) and outcome processing (reward positivity, RewP and late-positive potential, LPP) and ii) total power and phase synchrony of theta and delta band oscillations. Behaviorally, trial initiation was fastest after a near miss outcome and slowest after a winning outcome. As expected, a significant SPN was observed for possible wins (AA) vs. total misses (AB), consistent with reward anticipation. In addition, significantly larger win (AAA) vs. near miss (AAB) amplitudes were observed for the RewP and LPP to wins and LPP to near misses (vs. total misses) reflecting early and late-stage outcome processing effects. There was an effect of reel position on the RewP, with larger effects in the final reel (AAA-AAB) relative to the 2nd-reel locked difference waves (AA-AB). Across all outcomes, near misses elicited the largest and most phase-synchronized theta responses, while wins elicited larger and more phase-synchronized delta responses than total misses, with near misses not differing from wins or total misses. Phase locking measures contrasting win vs. near miss delta and theta synchronization, within time windows corresponding to ERP measurements, covaried with RewP, but not SPN or LPP, amplitude. Lastly, EEG measures showed differential relationships with age and self-reported consummatory pleasure. In the context of slot machine play, where reward anticipation and attainment place minimal demands on effort and skill, ERP and time-frequency methods capture distinct neurophysiological signatures of reward anticipation and outcome processing.

neuroscience↗

bioRxiv2019

Theta phase synchrony is sensitive to corollary discharge abnormalities in early illness schizophrenia but not in the clinical high-risk syndrome

BackgroundAcross the animal kingdom, responses in auditory cortex are dampened during vocalizing compared to passive listening, reflecting the action of the corollary discharge mechanism. In humans, it is seen as suppression of the EEG-based N1 event-related potential, with less N1-suppression seen in people with schizophrenia and those at clinical high risk (CHR) for psychosis. Because N1 is an admixture of theta (4-7Hz) power and phase synchrony, we asked which is responsible for N1 effects and if they outperform the sensitivity of N1 to corollary discharge and schizophrenia. MethodsTheta phase and power values were extracted from EEG data acquired from CHR youth (n=71), early illness schizophrenia patients (ESZ; n=84), and healthy controls (HC; n=103) as they said /ah/ (Talk) and then listened to the sounds played back (Listen). A principal components analysis extracted theta inter-trial coherence (ITC; phase consistency) and event related spectral power, peaking in the N1 latency range. ResultsTheta ITC-suppression (Cohen d=1.46) was greater than N1-suppression in HC (Cohen d=.63). Both were both reduced in ESZ, but only N1-suppression was reduced in CHR. When deprived of the variance shared with theta-ITC suppression, N1-suppression was no longer sensitive to HC vs. ESZ or HC vs. CHR group differences. Deficits in theta ITC-suppression were correlated with delusions (p=.007) in ESZ. Suppression of theta power was not affected by Group. ConclusionsTheta ITC-suppression may provide a simpler assay of the corollary discharge mechanism than N1-suppression. Deficits in circuits that generate low frequency oscillations may be an important component of schizophrenia.

neuroscience↗