LSD does more than disrupt brain rhythms: It speeds them up and increases signal complexity

A new international study has found that LSD changes the brain’s electrical activity in more ways than previously understood. The psychedelic not only alters the synchronization of brain waves but also accelerates their rhythms and makes neural signals more complex and less predictable.

The findings, published in *Communications Biology*, could help scientists better understand how psychedelics affect perception and consciousness and shed light on their potential use in treating depression and anxiety.

First synthesized in 1938 by Swiss chemist Albert Hofmann, lysergic acid diethylamide (LSD) is one of the most potent and extensively studied psychedelic substances. Even in very small doses, it can profoundly alter perception, producing visual hallucinations, distorting the sense of time and creating a feeling of unity with the surrounding environment.

After extensive psychiatric research in the 1950s and 1960s, LSD became associated largely with recreational and spiritual use. Over the past decade, however, scientific interest has revived as researchers investigate whether psychedelics could help treat conditions such as depression, anxiety and post-traumatic stress disorder.

Despite this renewed interest, the precise effects of LSD on the brain’s electrical activity remain incompletely understood. Scientists also want to determine whether its effects differ from those of other psychedelics.

LSD accelerates brain waves

To investigate these questions, an international research team analyzed magnetoencephalography (MEG) data collected at Imperial College London. MEG measures the tiny magnetic fields generated by electrical activity in the brain with millisecond precision.

The study involved 17 healthy volunteers who participated in two sessions held two weeks apart. During one session, participants received an intravenous dose of 75 micrograms of LSD. During the other, they received a placebo consisting of saline solution.

The researchers used advanced signal-processing techniques and artificial intelligence to examine changes in brain activity.

They found that LSD does not simply weaken alpha and beta brain waves, as earlier interpretations of psychedelic-induced brain activity might suggest. It also increases their frequency, meaning that the waves oscillate more rapidly.

Alpha-wave frequency rose by approximately 2 hertz, while beta-wave frequency increased by about 5 hertz across extensive areas of the cerebral cortex.

“Imagine a radio station switching its broadcast frequency from 99.5 to 100.5 FM,” explained Karim Jerbi, a professor in the University of Montreal’s Department of Psychology and a researcher at the Quebec Artificial Intelligence Institute. “If your radio stays tuned to 99.5, the signal may seem distorted or lost. In the same way, overlooking the shift to faster brain rhythms can lead us to misinterpret LSD’s effects on the brain.”

Alpha waves are commonly associated with relaxed wakefulness, particularly when the eyes are closed, while beta waves are linked to processes including concentration and decision-making.

The findings suggest that researchers need to distinguish between a genuine reduction in the strength of brain waves and a shift in their frequency. Unlike some anesthetics, which slow alpha rhythms, LSD appears to accelerate them, potentially reflecting increased cortical excitability.

Brain activity becomes more complex

The study also revealed changes beyond the speed of brain waves. Under LSD, neural signals became more complex, more fractal and less predictable.

Fractals are patterns that repeat across different scales. A familiar example is Romanesco broccoli, whose individual florets resemble miniature versions of the entire vegetable. In brain research, fractal properties describe signal patterns that recur across different time scales.

The researchers measured the fractal dimension of brain signals and the diversity of their patterns. Both increased after LSD administration, indicating that brain activity became richer in detail and more irregular.

The researchers compared this effect to the outline of a rugged coastline, which reveals additional bends and inlets as it is examined more closely, unlike the relatively uniform edge of a straight beach.

These changes were especially pronounced in brain regions involved in sensory perception, language, emotion and mental imagery. The motor cortex, which plays a key role in controlling movement, was comparatively unaffected.

This difference could help explain why psychedelics can profoundly alter perception and introspection without necessarily producing comparable disruptions in movement.

The findings also raise questions about a familiar feature of LSD experiences: the perception of intricate geometric patterns, including spirals, tunnels and endlessly repeating shapes, particularly when the eyes are closed.

A more fractal pattern of brain activity might be associated with these visual experiences, but the researchers emphasize that the connection has not yet been demonstrated.

“Our findings lend support to this intriguing hypothesis, but they do not yet confirm it,” Jerbi cautioned. “We measure the fractal structure of brain signals over time, not the fractal structure of the images people perceive.”

Artificial intelligence identifies LSD-related brain patterns

To determine whether these changes could reliably distinguish the effects of LSD from those of a placebo, the team trained a machine-learning algorithm to analyze brain signals.

By combining several measurements, the algorithm correctly identified whether a session involved LSD or a placebo in 88% of cases. By chance alone, it would have been expected to achieve an accuracy of 50%.

The distinguishing features included increased signal complexity and fractal dimension, changes in background neural activity, and shifts in the frequency and strength of alpha and beta rhythms.

“Our machine-learning algorithm can distinguish brain states under LSD from those under placebo using brain signals alone,” said Venkatesh Subramani, a doctoral researcher at the University of Montreal and a co-author of the study. “By examining the clues it relies on, we can identify LSD’s signatures in brain activity.”

What the findings could mean for psychedelic therapy

The study was conducted in healthy volunteers following a single dose of LSD and did not evaluate any therapeutic effects. Nevertheless, its findings could help scientists investigate how psychedelics alter patterns of thought and perception.

One influential theory proposes that psychedelics temporarily loosen the brain’s established expectations, allowing sensory information to exert a greater influence on perception. The faster and more complex neural activity observed in the study is consistent with this hypothesis, although it does not prove it.

This idea is particularly relevant to depression and anxiety, where people may become trapped in repetitive patterns of negative thinking. If psychedelics temporarily make brain activity more flexible, they might help people move away from these entrenched patterns. Whether this mechanism translates into clinical benefits remains to be established.

Meanwhile, an LSD-based formulation is being evaluated in phase 3 clinical trials for generalized anxiety disorder and depression, the final stage of testing before a treatment may be submitted for regulatory approval.

In further research, Subramani and his colleagues are using similar methods to compare LSD with psilocybin, the psychoactive compound in so-called magic mushrooms, and DMT, a naturally occurring psychedelic found in ayahuasca, a traditional South American preparation.

By comparing how these substances affect brain activity, the researchers hope to clarify their underlying mechanisms, track their effects and eventually identify which patients are most likely to benefit from psychedelic-assisted treatment.

The study, led by Venkatesh Subramani and colleagues from the University of Montreal, IMT Atlantique in France, the University of Auckland in New Zealand and the University of California, San Francisco, was published in Communications Biology.