Journal of Psychopharmacology
January 1, 2016
Jana Speth, Clemens Speth, Mendel Kaelen et al.
119 citations
A single dose of LSD (75 μg) reduced how often people spontaneously thought about the past, while thoughts about the present or future remained unchanged. In a placebo-controlled crossover study with 20 healthy volunteers, fewer references to past mental spaces appeared in reports collected about 2.5 hours after intravenous administration. This reduction correlated with the drug's subjective intensity and with decreased resting-state functional connectivity within the default-mode network, a brain system involved in autobiographical memory and rumination. The findings suggest LSD may reduce past-focused thinking, which could be relevant for treating conditions like depression where excessive reflection on the past is common.
Cognitive Science
March 22, 2016
Jana Speth, Trevor A. Harley, Clemens Speth
9 citations
The degree to which healthy people report hearing voices or talking to imaginary characters depends on their physiological state of consciousness. Analyzing 569 mentation reports from REM sleep, non-REM sleep, sleep onset, and waking, the study found that REM sleep produced the highest levels of auditory verbal experiences and agency, while sleep onset—traditionally linked to hallucinations—produced the lowest. The quantity and pragmatic features of these experiences vary systematically across states, indicating they are a function of the distinct physiological state in which they occur.
Schizophrenia Bulletin
October 1, 2025
Bryony Sheaves, Vanessa Cropley, Peter Moseley et al.
5 citations
Sleep dysfunction and hallucinatory experiences are bidirectionally related, with the strongest path leading from poor sleep to hallucinations. This narrative review examines mechanisms across four levels: phenomenology, psychology, neural networks, and neurophysiology. Stress is a well-supported mediator, with sleep manipulation studies in non-clinical populations showing its role. Sleep loss also affects nervous system inflammation, altering brain connectivity involved in hallucinations. Lived-experience accounts reveal three novel mechanisms—source monitoring, mental resilience, and reasoning skills—that are impacted by sleep loss, though the full causal chain requires further testing. Priorities include testing stress as a mediator in clinical populations and experimentally examining these novel mediators.
Cognitive Science
January 1, 2018
Clemens Speth, Jana Speth
Hallucinatory states occur naturally across the human sleep-wake cycle, not only with drugs or psychopathology. This study introduces a new measure of these states by analyzing mentation reports from sleep onset, REM sleep, and non-REM sleep. The reports were examined for motor agency (indicating interactions with an imagined world) and cognitive agency (enabling recognition of the hallucinatory state). Results show a decline in cognitive functions and an increase in simulated interactions with a hallucinatory world as sleep progresses toward REM sleep. The authors propose that REM sleep, with its high levels of simulated sensorimotor processes, may have evolved as a virtual laboratory for developing embodied cognition.
Consciousness and Cognition
February 1, 2017
Jana Speth, Astrid M Schloerscheidt, Clemens Speth
Mental time travel to the future is reduced during REM and non-REM sleep compared to waking. Three independent judges analyzed 563 mentation reports from sleep onset, REM sleep, non-REM sleep, and waking using a validated linguistic tool based on grammatical and cognitive-semantic theories. The data indicate that both REM and non-REM sleep are characterized by a reduction in future-oriented mental time travel, supporting earlier physiological evidence at the level of brain function.
Consciousness and Cognition
October 1, 2016
Jana Speth, Astrid M Schloerscheidt, Clemens Speth
Mental time travel to the future, but not to the past, decreases during sleep onset hypnagogia. Three independent judges analyzed 150 mentation reports collected before and after sleep onset, using a linguistic tool grounded in grammatical and cognitive-semantic theories. The results indicate that memory for the future diminishes at sleep onset, supporting preliminary physiological evidence at the level of brain function. This state of consciousness may help dissociate between mental time travel to the past and the future, despite recent research emphasizing similarities in their cognitive and physiological processes.
Consciousness and Cognition
April 1, 2016
Clemens Speth, Jana Speth
As people fall asleep, reflective thinking declines while motor imagery increases, indicating a shift toward interacting with an imaginary, hallucinatory world. In 150 mentation reports from 16 participants awakened at different times after sleep onset, cognitive and motor agency analysis—objective linguistic tools—showed a decrease in the reflective thinking needed to recognize the hallucinatory quality of the state, alongside an increase in motor imagery. These spontaneous changes in consciousness map onto physiological states, potentially aiding future exploration of conditions where consciousness declines and possibilities for treatment.