DATE: October 23, 2026 at 06:00AM
SOURCE: PSYPOST.ORG
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TITLE: LSD pushes brain activity toward a more fractal, complex state, study finds
URL: https://www.psypost.org/lsd-pushes-brain-activity-toward-a-more-fractal-complex-state-study-finds/
A new neuroimaging study indicates that lysergic acid diethylamide, commonly known as LSD, alters human brain activity not just by weakening regular brain waves, but also by speeding them up and making neural signals more complex. The weakening of brain waves and the rise in signal complexity were most pronounced in regions tied to sensory processing, language, emotion, and mental imagery, while areas that control physical movement were largely spared. The findings, published in Communications Biology, also hint that listening to music may dampen rather than amplify these drug-induced changes, though that trend did not hold up after statistical correction.
LSD is a potent psychedelic drug that temporarily alters perception, mood, and the sense of self. Like other classic psychedelics, it works primarily by attaching to and activating serotonin 2A receptors on brain cells, though LSD also binds to dopamine receptors. Studying how this compound changes large-scale brain activity helps scientists understand the biological processes that generate conscious experience.
In human studies, researchers often use magnetoencephalography, or MEG, to track the fast-paced electrical activity of the brain. MEG is a non-invasive procedure where a participant sits with their head inside a helmet-like scanner containing sensitive magnetic detectors. As groups of neurons fire together, they produce tiny magnetic fields that the scanner records at a millisecond-by-millisecond scale.
This electrical activity consists of two main types of signals: rhythmic brain waves and background noise. Rhythmic waves, or neural oscillations, happen when thousands of brain cells fire in a synchronized beat, much like a choir singing a specific note. Two of the most common resting rhythms are alpha waves, which cycle at about 8 to 13 times per second (measured in hertz, or Hz) during relaxed wakefulness, and beta waves, which cycle faster at 15 to 30 Hz and relate to active thinking and alertness. These rhythms ride on top of non-rhythmic, background electrical activity that naturally loses strength at higher frequencies.
Previous psychedelic studies consistently showed that drugs like LSD and psilocybin cause a widespread drop in the strength of alpha and beta waves, a process called cortical desynchronization. Because traditional brain wave analyses measure activity within fixed frequency windows, they can confuse a change in wave speed with a loss of wave strength, or mistake shifts in the background noise for changes in actual rhythms. If an alpha wave speeds up against a background that naturally falls off at higher frequencies, it can look as though the wave lost strength when it actually just shifted to a faster tempo.
Beyond brain wave speed and strength, psychedelics also change the unpredictability and structure of brain signals over time. Scientists measure this using two mathematical tools: Lempel-Ziv complexity, which counts how many new and distinct patterns appear in a signal over time, and Higuchi fractal dimension, which measures how “rough” or self-similar a signal looks when zoomed in and out across different time scales. Higher scores on both metrics indicate richer, less predictable brain activity.
The physical and social environment also plays a major role in shaping a psychedelic experience, with music frequently used in both traditional rituals and modern psychedelic-assisted therapy. For example, a study covered by PsyPost in 2018 showed that LSD heightened brain responses to music across regions tied to auditory processing, emotion, and memory. The new research was led by first author Venkatesh Subramani, who holds a doctorate in neuroscience, and senior author Karim Jerbi, a full professor in the psychology department, both of the Cognitive and Computational Neuroscience Laboratory (CoCo Lab) at the Université de Montréal. The team aimed to separate true changes in brain wave strength from shifts in wave speed and background activity, while also testing how music interacts with these electrical signatures.
“A characteristic effect of classic psychedelics is the desynchronization of rhythmic brain activity (that is, reduced coordination of activity among neural populations) in the alpha (8-13 Hz) and beta (15-30 Hz) bands,” Subramani told PsyPost. “LSD, however, appears somewhat unique because it also speeds up these intrinsic oscillations, by up to 2 Hz for alpha and up to 5 Hz for beta. This acceleration creates an ambiguity: it is unclear whether LSD genuinely desynchronizes these rhythms, or whether the previously reported desynchronization is an artifact of shifts in the spectral peaks.”
To investigate these questions, the researchers analyzed existing MEG data originally collected from 17 healthy volunteers. The experiment used a within-subject, single-blind, placebo-controlled design with a counterbalanced session order, meaning each participant completed two separate scanning sessions spaced 14 days apart without being told which treatment they were receiving. In one session, participants received an intravenous injection of 75 micrograms of LSD, and in the other, they received an inactive saline placebo.
Roughly four hours after the injection, participants underwent MEG brain scans under two different conditions, each lasting seven minutes. In the first condition, they rested with their eyes closed in silence. In the second condition, they kept their eyes closed while listening to ambient music excerpts. The research team used anatomical MRI scans of each participant’s head to map the MEG signals onto 360 distinct regions across the outer surface of the brain.
The authors then used a specialized mathematical tool to separate the rhythmic brain waves from the non-rhythmic background activity in each brain region. Instead of measuring wave strength inside rigid frequency boxes, they tracked the exact peak frequency where each participant’s alpha and beta waves were strongest. They also calculated Lempel-Ziv complexity and Higuchi fractal dimension for each region, and trained machine learning algorithms to see which brain features best distinguished the LSD state from the placebo state.
When the researchers separated the rhythmic waves from the background noise and accounted for shifting frequencies, they found that LSD still caused a genuine drop in the strength of alpha and beta waves. Alpha wave weakening was most pronounced in the temporal lobes, while beta wave weakening occurred broadly across the brain’s surface. However, ignoring the shifting frequencies made the wave weakening look much more widespread than it actually was, confirming that standard methods can inflate the apparent spatial extent of the drug’s effect.
“This study clarifies the ambiguity,” Subramani explained. “It shows that the weakening of oscillations, the usual marker of desynchronization, is genuine even after accounting for the peak shifts, a potential confound.”
Separating the signals also clarified what was happening in the posterior cingulate cortex, a major hub for self-reflection and daydreaming. In standard analyses that mix all signals together, this hub showed large drops in brain wave power under LSD. Once the background noise was removed, those rhythmic differences vanished, indicating that LSD mainly altered the background electrical activity in this region rather than its synchronized waves.
Alongside weakening the waves, LSD systematically sped them up across large portions of the brain. On average, the peak frequency of alpha waves increased by about 2 Hz, while beta wave peaks shifted upward by roughly 5 Hz. Machine learning models trained solely on these frequency shifts were able to correctly identify whether a scan came from an LSD or placebo session with over 82 percent accuracy, where chance would be 50 percent.
The background electrical activity also flattened out across the brain, meaning there was less slow background activity relative to fast activity. At the same time, both Lempel-Ziv complexity and fractal dimension rose substantially, especially in the back of the brain where visual information is processed. Machine learning decoders using these complexity and fractal measures distinguished the LSD state from placebo with over 76 percent accuracy, compared to a 50 percent chance level.
“In plain terms, LSD makes the brain’s main rhythms faster and weaker, and makes its activity more complex,” Subramani noted.
These results align with research covered by PsyPost in 2024, which examined brain activity under microdoses using EEG rather than full psychedelic doses using MEG, and similarly found that LSD increases neural signal complexity. The broader shift away from slower rhythms is also in line with a study covered by PsyPost in March 2026, which examined scalp EEG activity following psilocybin rather than source-resolved MEG following LSD and found that the drug weakened slower theta and alpha waves while strengthening faster beta and gamma activity. That study measured the strength of different frequency bands rather than the speed of individual rhythms, however, and the authors of the new paper note that a clear speeding of alpha and beta peaks has not been consistently observed with psilocybin.
To understand how these electrical changes relate to everyday mental functions, the researchers compared their brain maps against a massive database of over 14,000 prior brain imaging studies. They found that LSD’s effects followed distinct functional hierarchies across different brain systems. Reductions in alpha and beta wave strength, background flattening, and complexity increases were strongest in networks tied to vision, hearing, language, emotion, and mental imagery, while the motor cortex, which controls physical movement, remained largely unaffected.
The weakening and speeding of brain waves did not always line up. The functional systems that showed the largest drop in alpha wave strength, such as auditory and language networks, showed only minimal alpha speeding, while motor and attention networks retained relatively more of their alpha strength but showed the largest increases in alpha speed. In the beta range, the pattern reversed, with the biggest speed-ups occurring where beta strength dropped the most. Because the two effects were not statistically linked across the brain, the authors suggest that wave weakening and wave acceleration may reflect separate processes happening at the same time.
When the researchers examined the effect of music, they did not find any results that survived strict statistical corrections for multiple comparisons across the whole brain. However, uncorrected trends pointed in the opposite direction of what the team initially expected. Instead of boosting the brain effects of LSD, listening to music tended to slightly calm them down, resulting in less background flattening and lower signal complexity compared to experiencing LSD in silence.
The authors suggested that music might act as an external attentional anchor. Building on a 2024 analysis of this same dataset that found psychedelic-induced signal complexity was highest with eyes closed and dropped when attention turned outward, they propose that resting in silence allows the mind to wander freely into unconstrained internal states, whereas focusing on an external structured sound may gently ground and stabilize the brain’s electrical activity.
“Music can be very emotionally powerful, and music and psychedelics have been used together in rituals across many cultures,” Subramani said. “We wanted to formally test how music modulates the way LSD affects the brain. We hypothesized that music potentiates the effect of the drug. Somewhat surprisingly, and albeit not statistically robust, we found the opposite trend: music appeared to reduce the drug effect, which could suggest that the stimulus acts as an anchor that keeps subjects from fully experiencing the psychedelic state.”
“As noted in the paper, this is only hypothesis-generating,” he added. “It calls for studies with more subjects and targeted experimental designs with better controls.” He cautioned that “the music result is exploratory and should not be over-interpreted.”
There are a few things to keep in mind when interpreting these results. The study relied on a relatively small sample of 17 participants, which limits the statistical power needed to detect subtle interactions between the drug and external factors like music. In addition, the MEG scans were recorded about four hours after the LSD injection, roughly two and a half hours after the drug’s subjective effects had peaked. This timing gap may explain why the researchers found few strong links between the brain measurements and participants’ questionnaire ratings.
Looking at music over a single seven-minute average also treats a dynamic song as if it were a static event. Future studies with larger groups could track how brain waves respond to changing musical moments in real time, and use muscle sensors to help rule out muscle activity as a source of the fastest brain signals. Comparing LSD directly with other psychedelics using these same signal-separation methods will also help determine whether speeding up alpha and beta rhythms is a unique signature of LSD’s pharmacology.
The team is already extending their analytical approach to see how these faster brain wave frequencies might affect other common measures of brain communication, such as functional connectivity, which tracks how closely pairs of brain regions coordinate their activity over time.
“This study shows that LSD shifts the oscillatory peaks and that there is a genuine weakening of oscillations beyond these shifts,” Subramani said. “Power is one measure that could be confounded by peak shifts. Another is functional connectivity between pairs of brain regions. We have been actively working on this, and a preprint will be out shortly!”
The study, “LSD reconfigures cortical dynamics through faster brain rhythms and increased fractal dimension,” was authored by Venkatesh Subramani, Timothy Nest, Annalisa Pascarella, Jérémy Brunel, Yorguin José Mantilla Ramos, Yann Harel, Suresh Muthukumaraswamy, Robin Carhart-Harris, Giulia Lioi, Nicolas Farrugia, and Karim Jerbi.
URL: https://www.psypost.org/lsd-pushes-brain-activity-toward-a-more-fractal-complex-state-study-finds/
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