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）指某一干预手段所带来的有益心理生理结果，但其益处并非源于干预本身的固有属性，而是源自个体对该干预效果的预期。本研究旨在探讨预期如何影响神经认知过程。我们将通过设置三种双盲被试内实验条件来解答这一问题：参与者均被给予脱咖啡因咖啡，但分别被告知其摄入的是含咖啡因咖啡（条件i）、脱咖啡因咖啡（条件ii）；或参与者被给予含咖啡因咖啡，却被告知摄入的是脱咖啡因咖啡（条件iii）。在上述三种干预完成后，我们将记录参与者静息状态，以及完成持续注意力快速视觉信息处理任务（Rapid Visual Information Processing Task, RVIP）与Go/NoGo运动抑制控制任务期间的行为表现与脑电图（Electroencephalogram, EEG）数据。

本研究首先旨在验证既往研究结论：咖啡因可提升上述执行功能及其相关电生理指标的表现，具体包括注意P3成分、冲突响应N2成分与抑制P3成分（对比条件ii与iii）；随后验证预期亦可诱导此类效应的假说（对比条件i与ii），不过其效应幅度弱于咖啡因的直接作用（对比条件i与iii）。

针对行为学发现，我们未在两项探究任务的任一测量指标中，证实咖啡因摄入可带来行为提升的相关假说。而在电生理层面，我们证实咖啡因可提升注意P3成分与抑制P3成分的振幅，但对冲突响应N2成分无显著影响。此外，我们未找到证据表明预期会对任一探究的电生理指标产生影响。

最终我们证实，仅在与注意P3成分相关的全局场功率（Global Field Power, GFP）参数上，预期带来的效应幅度小于咖啡因的直接效应，且该现象仅出现于注意P3成分的某一参数中，其效应幅度同样弱于咖啡因的作用。据此我们认为，既往研究中所认定的咖啡因对行为层面的影响可能被高估；若预期对持续注意力与抑制控制并无实质性影响，那么其效应实则十分微弱。

最后，电生理层面的咖啡因效应表明，其倾向于调控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。