Debruille, J. B. | bioRxiv Science

bioRxiv2025

Cognitive effects of placebo antipsychotics: Investigating their mechanisms using event-related potentials (ERPs) in a cognitive test and a self-referential task

Placebos modulate neurocognitive processes. We examined whether a fully deceptive antipsychotic-placebo changes cognition not only by enhancing arousal and attention but also by changing self-representations, namely, by adding that of being under a treatment related to psychosis and by weakening the binding of experience to reality. Drug-naive healthy participants (N = 83) were split into a group (N = 40) who took a pill described as an antipsychotic and a no-pill control group (N = 43). Participants performed a cognitive test (CogTest), that is, a semantic categorization task and a self-referential role judgment task (SRT). Behavioral responses and event-related potentials (ERPs) were recorded. In the CogTest, placebos showed faster response times and higher accuracy than no-pills. This cognitive improvement was associated with more negative occipito-temporal early ERPs (OTEEs), larger central P2s (CentP2s), and larger late positive potentials (LPPs), with the latter correlating with response times. As in the literature, CentP2s were maximal in the SRT, possibly because it maximally stimulates the binding of the stimulus to long-term self-representations. The larger CentP2s and LPPs for placebos than for no-pills in the CogTest were thus tentatively related to the binding of the stimulus with egocentric self-representations, temporarily enriched by the addition of the representation of being on drug. On the contrary, the more negative OTEEs were related to a weaker binding to allocentric ones, preventing a strong binding of experience with reality. The smaller N400s observed for placebos than for no-pills in both tasks were related to greater openness to new experiences.

neuroscience↗

bioRxiv2018

A central component of the N1 event-related brain potential could index the early and automatic inhibition of the actions systematically activated by objects

Stimuli of the environment, like objects, systematically activate the actions they are associated to. These activations occur extremely fast. Nevertheless, behavioural data reveal that, in most cases, these activations are then automatically inhibited, around 100 ms after the occurrence of the stimulus. We thus tested whether this early inhibition could be indexed by a central component of the N1 event-related brain potential (ERP). To achieve that goal, we looked at whether this ERP component is greater in tasks that could increase the inhibition and in trials where reaction times happen to be long. The illumination of a real space bar of a keyboard out of the dark was used as a stimulus. To maximize the modulation of the inhibition, the task participants had to performed was manipulated across blocks. A look-only task and a count task were used to increase inhibition and an immediate press task was used to decrease it. ERPs of the two block-conditions where presses had to be prevented and where the largest central N1s were predicted were compared to those elicited in the press task, differentiating the ERPs to the third of the trials where presses were the slowest from the ERPs to the third of the trials with the fastest presses. Despite larger negativities due to motor potentials and despite greater attention likely in immediate press-trials, central N1s were found to be minimal for the fastest presses, intermediate for the slowest ones and maximal for the two no-press conditions. These results thus provide a strong support for the idea that the central N1 indexes an early and short lasting automatic inhibition of the actions systematically activated by objects. They also confirm that the strength of this automatic inhibition spontaneously fluctuates across trials and tasks. On the other hand, just before N1s, parietal P1s were found greater for fastest presses. They might thus index the initial activation of these actions. Finally, consistent with the idea that N300s index late inhibition processes, that occur preferentially when the task requires them, these ERPs were quasi absent for fast presses trials and much larger in the three other conditions.\n\nHighlightsEvent-related brain potentials (ERPs) elicited by a real object\n\nSmaller parietal P1s and greater central N1s for slowest than for fastest motor responses\n\nEven greater central N1s for tasks without such responses\n\nCentral N1s may index early inhibition of stimulus-activated actions\n\nN300s could index late inhibition of stimulus-activated actions

animal behavior and cognition↗