How Psychedelics Change the Brain

This four-minute explainer from NOVA (PBS) covers what functional brain imaging reveals about psychedelics like psilocybin: a quieting of the brain network tied to self-referential thought, and new research into a small structure called the claustrum. It centers on neuroscientist Fred Barrett, who proposes the claustrum may explain why brain activity reorganizes so sharply under a psychedelic. Claims are attributed to named researchers and framed as active, evolving research rather than settled fact.

The default mode network goes quiet

Under normal circumstances, the video explains, the default mode network activates when a person turns attention inward, and quiets when attention shifts outward. Brain imaging described in the piece shows this pattern flip under a psychedelic: the network tied to introspection quiets down, while other brain regions communicate more. Psylopedia's overview of the default mode network covers this mechanism in more depth, including its link to the sense of a fixed, narrating self.

A mathematical model in the video contrasts baseline brain activity with a brain under psilocybin. The psilocybin model shows a sharp rise in what the video calls global communication: thousands of new connections forming between regions that don't typically talk to each other.

A shaken snow globe

One interviewee reaches for a household image to describe this from the inside. Ordinarily, brain activity is like snow settled at the bottom of a globe: fixed, orderly. A psychedelic, in this analogy, is like picking the globe up and shaking it, so the settled pattern gives way to something more random, even chaotic. Researchers connect this reorganization to the altered, heightened awareness people often report during the experience.

The claustrum: a possible switchboard

The video's more novel material concerns the claustrum, a thin sheet of gray matter tucked deep within each brain hemisphere. According to Fred Barrett, animal studies have found the claustrum densely connected to nearly every other brain region, and its receptors overlap with the ones psychedelics target. That overlap led his team to ask whether the claustrum sits at the center of psychedelic effects.

Barrett describes the claustrum's normal role as something like a switchboard, helping other brain regions coordinate when to activate and quiet down. His working hypothesis is that a psychedelic binds to claustrum receptors and disrupts that coordinating function. "It's almost as if the switchboard walks away," he says. What follows, in his account, is a marked change in how brain regions communicate, a shift he ties to new learning and possibly some reorganization of the circuits that shape behavior.

What it might mean for lasting change

The video treats this as a possible explanation, not a settled one. Barrett suggests the claustrum's sudden loss of control may be part of why rigid thought and behavior patterns become more open to change during and after a psychedelic experience, a theme Psylopedia explores further in its overview of neuroplasticity. One person interviewed for the piece describes headaches and muscle pain afterward as evidence, in their words, that "the psilocybin was working," comparing the process to reprogramming a computer's operating system down to its basic code. This is a personal account, not a clinical finding, and the video does not present it as typical or guaranteed.

For more on how researchers map psychedelic effects on brain activity, see Psylopedia's article on how psychedelics change the brain. The substance discussed here, psilocybin mushrooms, has its own dedicated profile.

Key takeaways

• ●The default mode network, active during introspection, tends to quiet under a psychedelic like psilocybin, per the brain imaging described in the video.
• ●Communication between other brain regions appears to increase sharply, with thousands of new connections forming.
• ●One interviewee compares this shift to shaking a snow globe: a settled, orderly pattern gives way to something more random.
• ●Neuroscientist Fred Barrett's research centers on the claustrum, a small, densely connected structure that may normally help coordinate brain activity.
• ●Barrett's hypothesis: psychedelics disrupt the claustrum's coordinating role, likening it to a switchboard operator walking away.
• ●The video links this disruption to possible new learning and looser behavior patterns, framed as active research, not a settled conclusion.
• ●A personal account in the piece is anecdotal and should not be read as typical or guaranteed.