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Blinding integrity in psychedelic research: Evidence from a comparative randomized controlled trial of psilocybin, MDMA, and methylphenidate in healthy volunteers.

Maintaining effective blinding is a major methodological challenge in psychedelic research. This study provides a comprehensive evaluation of blinding integrity in 120 healthy volunteers who received either psilocybin, MDMA, or methylphenidate (active placebo) in a double-blind, randomized controlled trial. Using a multi-level assessment incorporating forced-choice substance guesses, certainty ratings, decision factors, and subjective substance effects, the analyses characterize blinding integrity and its relation to the substance experience. Results indicate that overall blinding was insufficient, with psilocybin showing the highest rates of functional unblinding, MDMA moderate levels, and methylphenidate the lowest. As an active placebo, methylphenidate provided more effective blinding for MDMA than for psilocybin. Incorporating certainty levels of substance guesses revealed a more differentiated pattern, with lower functional unblinding rates. Decision factors and subjective substance experiences were associated with phenomenological substance effects. Prior substance experiences did not influence accuracy of forced-choice substance guesses. These findings provide empirical guidance for the design and reporting of blinding procedures in psychedelic trials and underscore the value of systematic, multi-level assessment of blinding integrity.

Humans

Pharmacological and non-pharmacological modulation of striatal dopamine release: a meta-analysis of [11C]raclopride PET studies.

The dopaminergic system has long been a central focus of functional neuroimaging. Positron emission tomography (PET) with the D2/D3 receptor radioligand [11C]raclopride remains the most widely used method for indirectly quantifying striatal dopamine release in vivo. However, no previous meta-analysis has studied the relative magnitude and regional distribution of dopamine release across different interventions or cognitive interventions overall. To address this gap, in this meta-analysis of 92 [11C]raclopride PET studies (n&#x2009;=&#x2009;1640), we compared the magnitude and regional distribution of dopamine release induced by amphetamine, methylphenidate, ketamine, alcohol, and cognitive challenges with and without reward. Amphetamine induced approximately four-fold greater dopamine release than cognitive challenges (10.9 vs. 2.7%, p&#x2009;<&#x2009;0.001), and approximately twice that of alcohol (4.8%, p&#x2009;<&#x2009;0.001), with effects comparable to methylphenidate (11.5%) and slightly greater than ketamine (9.8%). Psychostimulant-induced increase in synaptic dopamine was greater in putamen and ventral striatum than in caudate, whereas alcohol preferentially engaged ventral striatum. Dopamine release did not differ between rewarded and non-rewarded cognitive tasks in the ventral striatum (p&#x2009;>&#x2009;0.14) or overall striatum (p&#x2009;>&#x2009;0.10). Methylphenidate-induced increases in synaptic dopamine appeared to attenuate with advancing age, whereas cognitive challenges were associated with greater dopamine release in older individuals. These findings demonstrate that individual pharmacological and cognitive interventions differ markedly in both magnitude and regional pattern of dopamine release. They also suggest that [&#xb9;&#xb9;C]raclopride PET may have limited sensitivity for distinguishing reward-related from non-reward-related dopamine release. These findings have implications for the design and interpretation of future neuroimaging studies of dopaminergic function in health and disease.

Journal Article

Catecholaminergic Contributions to Inhibitory Control Following Physical Fatigue: Behavioral and Neurophysiological Findings.

Acute physical fatigue can impair cognitive control, yet its underlying neurochemical mechanisms remain unclear. This study investigated whether catecholaminergic modulation influences behavioral and neural markers of inhibitory control following physical fatigue. Eighteen healthy, recreationally active adults (9 males, 9 females; 23.4&#xa0;&#xb1;&#xa0;2.2&#xa0;years) completed a randomized, triple-blind, placebo-controlled crossover study. On separate visits, participants received methylphenidate (MPH; 20&#xa0;mg; a dopamine and noradrenaline reuptake inhibitor), reboxetine (REB; 8&#xa0;mg; a noradrenaline reuptake inhibitor), or placebo. Physical fatigue was induced by repeated bilateral leg extensions to task failure. Cognitive performance was assessed before and after physical fatigue using a Go/No-Go task with electroencephalographic recording. Behavioral outcomes included reaction time and accuracy, while event-related potentials measured neural stages of response execution and inhibition (N2 and P3). Mixed-effects models were used for statistical analysis. For No-Go trials, a significant MPH&#xa0;&#xd7;&#xa0;Time interaction was observed for accuracy (p&#xa0;=&#xa0;0.008), with improved post-fatigue performance following MPH administration (p&#xa0;=&#xa0;0.048). At the neural level, MPH was associated with shorter fronto-central No-Go N2 latency (p&#xa0;=&#xa0;0.038) and altered fatigue-related changes in No-Go P3 latency (p&#xa0;=&#xa0;0.047). REB did not produce comparable behavioral or neural effects. These findings provide pharmacological evidence that catecholaminergic mechanisms contribute to inhibitory control following physical fatigue. The differential effects of MPH and REB suggest that selective noradrenergic enhancement alone is insufficient to maintain inhibitory control following physical fatigue. Instead, the findings implicate broader&#xa0;dopaminergic and noradrenergic mechanisms, potentially involving alterations in the temporal dynamics of inhibitory processing. TRIAL REGISTRATION: (G095422N and identifier NCT05880342).

Adult