Brain scans show LSD fragments local neural activity to reshape consciousness

Researchers scanning the brains of people on LSD have discovered something counterintuitive: the drug doesn't amplify neural activity so much as it fragments it. By quieting the electrical rhythms that normally keep nearby brain cells synchronized, LSD forces the brain to abandon its usual way of processing the world—and in doing so, fundamentally reshapes what consciousness feels like.

The finding comes from a study led by Paolo La-Torraca-Vittori at the University of Pavia and Livio Tarchi at the University of Florence, published in the European Journal of Neuroscience. The researchers analyzed brain scans from 15 healthy adults who underwent two imaging sessions roughly two weeks apart. In one session, participants received a saline placebo. In the other, they received a moderate dose of LSD intravenously. The scans took place about an hour after administration, capturing the peak of the psychedelic experience, with participants resting inside the scanner with their eyes closed.

Most previous neuroimaging studies of psychedelics have focused on large-scale communication between distant brain networks. This research instead zoomed in on what happens at the local level—in the tiny clusters of neurons that normally fire together in coordinated patterns. The team measured two specific metrics: the amplitude of low-frequency fluctuations, which captures the strength of slow, spontaneous brain waves in a localized area, and regional homogeneity, which assesses how well neighboring neurons synchronize their electrical activity. Under LSD, both metrics dropped significantly, particularly in the visual and somatosensory cortices—the brain regions that process sight and touch.

This local fragmentation has profound consequences for how the brain organizes information. Normally, the human brain operates like a hierarchy. Sensory regions at the bottom process raw inputs—light, sound, touch—and pass that data up the chain to associative regions that interpret and make sense of it. This division of labor keeps different types of information in separate channels. But when LSD desynchronizes local activity, this structured hierarchy collapses. Instead of visual information staying in the visual cortex and somatosensory information staying in its own region, the brain begins integrating sensory data broadly across the entire cortex. Visual and physical sensations blend together. The boundaries between different types of perception dissolve.

The drug's effects rippled through other brain systems as well. Low-frequency fluctuations dropped heavily in the default mode network, a collection of brain areas that activate during rest, daydreaming, and self-reflection. Disruptions in this network align closely with the dissolution of the conscious self that many psychedelic users report—the sense that the boundary between self and world has become permeable or vanished entirely. Regional homogeneity also decreased in deep subcortical structures like the thalamus and amygdala, which act as central relay stations for sensory information and emotional processing. When local synchronization breaks down in these hubs, it changes how sensory signals get routed through the brain.

When the researchers mapped these functional changes onto the brain's chemical landscape, they found something unexpected. While some of the effects correlated with LSD's primary target—the 5-HT2A serotonin receptor—the drops in both brain metrics also mirrored the distribution of dopamine D2 receptors and an alternative serotonin receptor called 5-HT1A. This suggests that LSD's mind-altering power doesn't come from a single chemical pathway but from a cascade of neurochemical events spanning multiple messenger systems. The drug may directly activate some receptors while indirectly triggering others, producing the rich tapestry of sensory and emotional shifts that characterize the experience.

The findings align with what neuroscientists call the entropic brain hypothesis—the idea that psychedelics push the brain into a state of higher entropy, or greater disorder and randomness. In physics, entropy measures disorder. In neuroscience, higher entropy means the brain is generating a richer, less predictable pattern of states. By fragmenting local synchronization, LSD increases this entropy, allowing for more flexible and dynamic thought processes. The brain becomes less constrained by its usual hierarchical organization, more capable of making novel connections.

The researchers acknowledge significant limitations. The study involved only 15 participants, a small sample that requires replication in larger, more diverse populations. The team relied on standardized maps of receptor density from a general population rather than imaging the actual participants' brains, which reduces the precision of the chemical correlations. The resting scans also took place after a music-listening session, and the emotional or neurological effects of that music could have influenced the results independently of the drug. These caveats matter, but they don't diminish the core insight: LSD works by breaking apart the brain's normal local coordination, forcing it to integrate information in radically new ways.

As researchers continue mapping how altered brain chemistry reshapes consciousness, these findings offer a foundation for developing safer, more targeted psychedelic therapies. The next step will be comparing these localized measures with other brain monitoring technologies to pinpoint both where and when these neural changes occur. Understanding the mechanics of consciousness alteration at this level of detail could eventually allow clinicians to harness psychedelics' therapeutic potential while minimizing unwanted effects.