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BackgroundPsychiatric and neurodegenerative illnesses are characterized by cognitive impairments, in particular deficits in working memory, decision-making, and executive functions including cognitive flexibility. However, the neuropharmacology of these cognitive functions is poorly understood. The serotonin (5-HT) 2A receptor might be a promising candidate for the modulation of cognitive processes. However, pharmacological studies investigating the role of this receptor system in humans are rare. Recent evidence demonstrates that the effects of Lysergic acid diethylamide (LSD) are mediated via agonistic action at the 5-HT2A receptor. Yet, the effects of LSD on specific cognitive domains using standardized neuropsychological test have not been studied.MethodsWe examined the acute effects of LSD (100 µg) alone and in combination with the 5-HT2A antagonist ketanserin (40 mg) on cognition, employing a double-blind, randomized, placebo-controlled, within-subject design in 25 healthy participants. Executive functions, cognitive flexibility, spatial working memory, and risk-based decision-making were examined by the Intra/Extra-Dimensional shift task (IED), Spatial Working Memory task (SWM), and Cambridge Gambling Task (CGT) of the Cambridge Neuropsychological Test Automated Battery.ResultsCompared to placebo, LSD significantly impaired executive functions, cognitive flexibility, and working memory on the IED and SWM, but did not influence the quality of decision-making and risk taking on the CGT. Pretreatment with the 5-HT2A antagonist ketanserin normalized all LSD-induced cognitive deficits.ConclusionsThe present findings highlight the role of the 5-HT2A receptor system in executive functions and working memory and suggest that specific 5-HT2A antagonists may be relevant for improving cognitive dysfunctions in psychiatric disorders.

Adapting one's attitudes and behaviors to group norms is essential for successful social interaction and, thus, participation in society. Yet, despite its importance for societal and individual functioning, the underlying neuropharmacology is poorly understood. We therefore investigated its neurochemical and neural correlates in a pharmacological functional magnetic resonance imaging study. Lysergic acid diethylamide (LSD) has been shown to alter social processing and therefore provides the unique opportunity to investigate the role of the 5-HT 2A receptor in social influence processing. Twenty-four healthy human volunteers received either (1) placebo + placebo, (2) placebo + LSD (100 µg), or (3) the 5-HT 2A receptor antagonist ketanserin (40 mg) + LSD (100 µg) at three different occasions in a doubleblind, randomized, counterbalanced, cross-over design. LSD increases social adaptation but only if the opinions of others are similar to the individual's own. these increases were associated with increased activity in the medial prefrontal cortex while participants received social feedback. furthermore, pretreatment with the 5-HT 2A antagonist ketanserin fully blocked LSD-induced changes during feedback processing, indicating a key role of the 5-HT 2A system in social feedback processing. our results highlight the crucial role of the 5-HT-system in social influence and, thus, provide important insight into the neuropharmacological basis of social cognition and behavior. The quality and quantity of individuals' social relationships has been tightly linked to morbidity and mortality 1. Social influence is omnipresent in our everyday life and reacting to the opinions of others is deeply rooted in human nature 2. Every time people interact or communicate, be it in real life or virtually, people are influenced by each other. Social adaptation refers to the act of changing one's attitudes, beliefs, or behaviors to match social norms that are implicitly or explicitly shared by a group of individuals 3. Zaki et al. 4 suggest that exposure to social norms directly influences participants' neural representations of the value they assign to stimuli. Being susceptible to social influence is essential for successful social interaction and communication, and also for the functioning and organization of an entire society. However, it can also have negative consequences if misused 5,6. In recent years, social neuroscience has advanced our understanding of the neural systems underlying social influence processing 7-9. Amongst other brain regions, it has been shown that frontal regions as well as the reward system are strongly implicated in adaptation to group norms 10-12. In particular, when exposed to a mismatch between the own and the group opinion, participants showed a deactivation of the ventral striatum and an

As source of sensory information, the body provides a sense of agency and self/non-self-discrimination. The integration of bodily states and sensory inputs with prior beliefs has been linked to the generation of bodily self-consciousness. The ability to detect surprising tactile stimuli is essential for the survival of an organism and for the formation of mental body representations. Despite the relevance for a variety of psychiatric disorders characterized by altered body and self-perception, the neurobiology of these processes is poorly understood. We therefore investigated the effect of psilocybin (Psi), known to induce alterations in self-experience, on tactile mismatch responses by combining pharmacological manipulations with simultaneous electroencephalography–functional magnetic resonance imaging (EEG–fMRI) recording. Psi reduced activity in response to tactile surprising stimuli in frontal regions, the visual cortex, and the cerebellum. Furthermore, Psi reduced tactile mismatch negativity EEG responses at frontal electrodes, associated with alterations of body- and self-experience. This study provides first evidence that Psi alters the integration of tactile sensory inputs through aberrant prediction error processing and highlights the importance of the 5-HT2A system in tactile deviancy processing as well as in the integration of bodily and self-related stimuli. These findings may have important implications for the treatment of psychiatric disorders characterized by aberrant bodily self-awareness.