Low-dose LSD and the stream of thought: Increased Discontinuity of Mind, Deep Thoughts and abstract flow

William James' metaphor of a 'stream of thought' frames freely roaming cognition as continuous, dynamic and relatively unconstrained. The authors distinguish two modes of this stream: a passive, task-unrelated form typically labelled mind-wandering, and an active, stimulus-related form assessable by free association. Previous literature indicates that classic serotonergic psychedelics (for example LSD, psilocybin, ayahuasca) substantially alter perception, cognition and language, with anecdotal and some empirical evidence pointing to disinhibited, associative, imagery-rich and less context-bound thinking under these compounds. However, systematic, time-resolved investigations of how psychedelics affect the stream of thought—both passive and active components—have been sparse. Wießner and colleagues set out to characterise the time-dependent effects of a low dose of LSD (50 μg) on passive and active stream-of-thought processes in healthy volunteers. Specifically, the study tested two hypotheses: that LSD would alter mind-wandering during resting state and that it would increase forward flow (a measure of semantic evolution) during a chain free-association task. The authors emphasise the time course of effects, assessing multiple post-administration points to detect transient windows of altered thought and affect that could have technical and therapeutic relevance.

Design and participants: The study used a randomised, double-blind, placebo-controlled crossover design with two treatment sessions (LSD 50 μg, inactive placebo) separated by a 14-day washout. Twenty-five volunteers were recruited and screened medically and psychiatrically; one withdrew after the first session so the analysed sample comprised 24 participants (8 women; mean age 35 ± 11 years, range 25–61). Inclusion required at least one prior LSD experience and specified substance-abstinence periods before sessions; major psychiatric, cardiovascular or other contraindications led to exclusion. Drug and setting: LSD (> 99% purity) or matched placebo was administered orally in 30 ml water at 9:30 a.m. The dose is described as low and was delivered in a comfortable, living-room style environment. Because participants had prior LSD experience and the dose was modest, investigators minimised pre-session suggestion by providing only basic written consent information about possible risks. Outcome measures and schedule: Two complementary measures probed the passive and active stream of thought. Passive mind-wandering was assessed with the Amsterdam Resting State Questionnaire 2.0 (ARSQ), a 55-item self-report yielding ten factor scores (for example Discontinuity of Mind, Visual Thought) plus 20 additional items (including Deep Thoughts, Thoughts about Sounds, Thoughts about Odours). For each ARSQ assessment, participants sat with eyes closed for a 5-minute resting period and then completed the questionnaire referring to that interval. Active stream of thought was assessed with a chain free-association task called the Forward Flow Task (FFT). For FFT, participants produced a chain of 20 words starting from a seed word and three seed types were used (animals, objects, abstract words); each chain was typed on a computer and completion time recorded. Semantic distances between words were computed using FastText embeddings on a Portuguese Wikipedia corpus; from the resulting 21 × 21 distance matrices the team extracted Forward Flow (average distance of each word to all predecessors), Flow Distance (average distance of the seed to subsequent words) and Flow Steps (average distance between adjacent words). Flow Distance and Flow Steps were newly developed exploratory parameters. Timing and ancillary procedures: Baseline ARSQ and FFT were administered immediately before dosing (+0 h). Subjective intensity and valence were sampled frequently with visual analogue scales (VAS) in short intervals for the first 2 h and then at 30-minute intervals up to +8 h; ARSQ and FFT were repeated at +2 h, +4 h, +6 h, +8 h and the following morning (+24 h). Participants were allowed quiet, nondemanding activities between tasks and were discharged only after investigators confirmed stability at +8 h. Statistical analysis: Repeated-measures general linear models (GLMreps) treated treatment and time point as within-subjects factors and treatment order as a between-subjects factor. For ARSQ and FFT an additional within-subjects factor 'parameter' was included as appropriate. Pairwise comparisons at each time point/parameter were performed. Effect sizes were reported as partial eta squared. Multiple comparisons were controlled with the Benjamini–Hochberg procedure (false discovery rate q = 0.05) across defined families of tests. Spearman rank correlations were computed between LSD-induced change scores (Δ = LSD − placebo) for intensity, valence, ARSQ and FFT measures, with p-values adjusted for the number of scales (N = 4). The authors used IBM SPSS Statistics version 22.

Sample and dosing: Twenty-four healthy participants completed both sessions and were included in analyses. Each received 50 μg LSD or placebo in a double-blind, crossover manner. Subjective intensity and valence: LSD produced a significant main effect on subjective intensity (p < 0.001) and a treatment × time interaction (p = 0.008), indicating time-dependent increases in reported intensity under LSD versus placebo. Pairwise comparisons showed higher intensity for LSD than placebo from +0.5 h through +8 h (all p ≤ 0.025). Valence also differed by treatment (main effect p = 0.001) without a treatment × time interaction; pairwise tests indicated more positive valence for LSD at multiple intervals (+1 h to +4.5 h, +5.5 h, and +6.5 h to +7.5 h; all p ≤ 0.021). A period effect (session 2 lower intensity; p = 0.009) and an order effect (higher intensity when LSD was given in the first session; p = 0.039) were observed for intensity, suggestive of habituation and carryover influences; no period or order effects were reported for valence. Mind-wandering (ARSQ): Rather than a single-factor change, the authors identified a pattern of ARSQ factor/item changes that they grouped qualitatively into three facets: a 'chaotic' facet, a 'meaning' facet and a 'sensory' facet. The chaotic facet included increased Discontinuity of Mind and changes in items such as Sleepiness, Planning, Thoughts under Control, Thoughts about Work and Thoughts about Past; this facet was most pronounced from +2 h to +6 h. The meaningful facet comprised increased Deep Thoughts and Not Sharing Thoughts and reduced Feeling Bored, peaking between +2 h and +4 h (Deep Thoughts sustained until +4 h; Not Sharing Thoughts seen at +2 h). The sensory facet, seen at +2 h, included increased Thoughts about Odours and Thoughts about Sounds. The extracted text indicates that several ARSQ factors and items reached significance and that these were aggregated into the three facets, but the full table of exact factor-level statistics is reported elsewhere in the paper. Chain free association (FFT): No overall treatment main effect emerged for FFT across seed types, duration or semantic spread. However, pairwise comparisons showed that LSD increased all three flow parameters (Forward Flow, Flow Distance, Flow Steps) for abstract seed words at +4 h (all p ≤ 0.05). There were no significant LSD effects for animal or object seed words, nor at other time points. Period effects (lower means in session 2) were observed for animal and object flows and for task duration, suggesting learning or habituation across sessions. Correlations: Early increases in subjective intensity (ΔInt at +0.5 h to +1.5 h) correlated moderately with later valence increases (ΔVal at +1.5 h, +7 h, +7.5 h) and with ΔARSQ Thoughts about Odours at +2 h; early intensity correlated negatively with ΔFFT flow distance at +4 h. Within ARSQ, several moderate correlations were reported—for example, Δ Discontinuity of Mind correlated with Feeling Restless (+2 h); Planning correlated with Thoughts about Work (+2 h); Deep Thoughts at +2 h correlated with Deep Thoughts at +4 h; Thoughts under Control at +2 h correlated with that at +4 h; and Discontinuity of Mind correlated negatively with Thoughts under Control at +4 h. Within FFT measures, moderate to high positive intercorrelations were observed. The authors note that mind-wandering and FFT effects were not correlated, implying largely independent modulations of passive and active stream-of-thought measures.

Wießner and colleagues interpret their findings as evidence that a low, psycholytic-range dose of LSD alters multiple dimensions of the stream of thought in a time-dependent manner. The subjective-intensity profile peaked around +2 h and remained elevated to +8 h; valence showed increased positive ratings across several intervals. The authors categorise LSD-induced changes in resting-state thought into three conceptual facets: a chaotic facet (increased discontinuity and disorganisation of thought, spanning approximately +2 h to +6 h), a meaningful facet (increased Deep Thoughts and reduced boredom, approximately +2 h to +4 h) and a sensory facet (transient increases in thoughts about smells and sounds at +2 h). Free-association analyses revealed an 'abstract flow' effect at +4 h, with greater semantic movement for abstract seed words but not for concrete categories. These results are positioned relative to earlier anecdotal and experimental reports of loosened associations, increased imagery and reduced cognitive control under psychedelics. The authors suggest that LSD may reduce attentional control and contextual integration, producing more associative and meaning-laden semantic processing—effects that appear stronger for abstract than for concrete content. Timing is highlighted as clinically relevant: a later phase (around +4 h) combining reduced intensity/confusion with increased positive valence, meaning and abstract associative flow could represent a favourable window for psychotherapeutic engagement in psycholytic protocols. The authors acknowledge several limitations. Self-report assessments of brief resting-state episodes may be vulnerable to memory bias, particularly given LSD's known effects on short-term memory; although ARSQ validation items did not suggest impaired evaluative capacity, this remains a concern. The grouping of ARSQ changes into qualitative facets was exploratory and requires statistical confirmation in subsequent work. Two FFT-derived measures (Flow Distance, Flow Steps) are newly introduced and need independent validation. The semantic analyses depended on a Portuguese Wikipedia corpus that is less comprehensive than English resources, which may influence embedding quality and cross-language comparability. The smaller and sometimes weaker effects in FFT compared with ARSQ could reflect methodological differences (objective semantic-distance computations versus subjective self-report), true dissociations between spontaneous and stimulus-induced thought, or simply limited power given the modest sample size. Finally, the sample comprised healthy, experienced LSD users, so generalisability to clinical populations is untested. Implications noted by the investigators include both a technical contribution—demonstrating a time-specific, multifaceted phenomenology of the 'psychedelic mind'—and a potential therapeutic implication, namely that low-dose LSD may transiently increase meaningful, symbol-rich associative thinking while preserving positive affect, a combination that could be harnessed in psycholytic therapy. The authors recommend further work to replicate findings, validate novel measures, explore clinical populations and test the proposed late therapeutic window under controlled therapeutic designs.

The study reports that a single low dose of LSD (50 μg) modulates the stream of thought in healthy volunteers across several dimensions and time points. Specifically, LSD increased a transient chaotic disorganisation of spontaneous thought, a shorter-lived increase in meaning-laden thinking, transient sensory-focused thoughts, and an elevated abstract associative flow during free association around +4 h. The concurrence of increased positive valence, meaning and abstract flow during the later phase suggests a possible late therapeutic window for psycholytic approaches, a hypothesis the authors recommend testing in future clinical research.