Neural correlates of expectations-induced effects of caffeine intake on executive functions

ABSTRACT Placebo effects (PE) are defined as the beneficial psychophysiological outcomes of an intervention that are not attributable to its inherent properties; PE thus follow from individuals’ expectations about the effects of the intervention. The present study aims aimed at examining how expectations influence neurocognitive processes. We will addressed this question by contrasting three double-blinded within-subjects experimental conditions in which participants are were given decaffeinated coffee, while being told they have had received caffeinated (condition i) or decaffeinated coffee (ii), and given caffeinated coffee while being told they have had received decaffeinated coffee (iii). After each of these three interventions, performance and electroencephalogram will bewas recorded at rest as well as during sustained attention Rapid Visual Information Processing task (RVIP) and a Go/NoGo motor inhibitory control task. We first aimed to confirm previous findings for caffeine-induced enhancement on these executive components and on their associated electrophysiological indexes (attentional P3 component, response conflict N2 and inhibition P3 components (ii vs iii contrast); and then to test the hypotheses that expectations also induce these effects (i vs ii), although with a weaker amplitude (i vs iii). Related to the behavioral findings, wWe didn’t not confirm any of our hypotheses for behavioral improvement induced by caffeine intakeon either of the investigate tasks’ measures. Regarding the neurophysiological findingsAt the electrophysiological level, however, we confirmed that caffeine effects on increased the attentional P3 and inhibition P3 components amplitude, but not on the response conflict N2 component. Additionally, wWe dodid not confirm provide evidence that expectations do not influence any of the investigate electrophysiological indexeices. Finally, we confirm that that expectations effects are smaller compared to caffeine effects but only for the Global Field Power parameter related to the attentional P3 component. only for one of the investigated the attentional P3 component’s parameters, and that this effect was smaller than that of We conclude that Hence, previously identified caffeine effects at the behavioral level may have been overestimated and that if while expectations effects have any no influence on sustained attention and inhibitory control, they are small. XXCaffeine effects at the electrophysiological level indicate that it tends to modulate brain areas underlying attentional mechanisms in both RVIP and Go/NoGo tasks rather than being specific to inhibitory control processes.摘要 安慰剂效应（Placebo effects, PE）指某干预措施所产生的有益心理生理结果，但其效应并非源于干预措施本身的固有属性，而是源自个体对该干预措施效应的预期。本研究旨在探讨预期如何影响神经认知过程。 本研究通过对比三种双盲被试内实验条件解答了上述问题：向被试提供脱因咖啡，但告知其饮用的是含咖啡因咖啡（条件i）或脱因咖啡（条件ii）；以及向被试提供含咖啡因咖啡，但告知其饮用的是脱因咖啡（条件iii）。 在三种干预措施实施后，我们记录了被试在静息状态下，以及持续注意力快速视觉信息处理任务（Rapid Visual Information Processing task, RVIP）、Go/NoGo运动抑制控制任务中的行为表现与脑电图（electroencephalogram, EEG）信号。 本研究首先验证了既往研究中咖啡因对上述执行成分及其相关电生理指标的增强效应：包括注意力P3成分、反应冲突N2成分以及抑制P3成分（对比条件ii与iii）；随后检验了预期也可诱发此类效应的假设（对比条件i与ii），不过预期效应的幅值更低（对比条件i与iii）。 在行为结果方面，我们未验证到咖啡因摄入可改善任一探究任务指标的相关假设。在电生理层面，本研究证实咖啡因可提升注意力P3与抑制P3成分的幅值，但对反应冲突N2成分无显著影响。此外，我们未找到预期会影响任一探究电生理指标的证据。最后，我们证实仅在与注意力P3成分相关的全局场功率（Global Field Power, GFP）参数上，预期效应的幅值低于咖啡因效应，且该效应仅存在于单个被探究的注意力P3成分参数中，其幅值亦小于咖啡因效应。 综上，既往研究中报道的咖啡因在行为层面的效应可能被高估；即便预期效应未对持续注意力与抑制控制产生显著影响，其效应量也极小。电生理层面的咖啡因效应表明，咖啡因倾向于调控RVIP与Go/NoGo任务中参与注意力机制的脑区，而非仅特异性作用于抑制控制过程。