Mind & behavior
LSD scans linked visual activity to more of the brain—even with eyes closed
The imaging study linked changes in brain activity to reported experiences. Its measures show associations across a small sample, not a complete explanation of hallucination.
Seeing with closed eyes
The 2016 study led by Robin Carhart-Harris used several imaging methods to examine the LSD experience. Participants were scanned with their eyes closed. Under LSD, visual-cortex activity showed stronger functional connections with a broader set of brain regions, and the changes were associated with reported visual experiences.
The sample needs careful description. Twenty healthy participants attended the LSD and placebo sessions; the functional-connectivity figures used 15 participants with usable data. Saying simply that the study had 15 volunteers erases the distinction between recruitment and the analysis population. That distinction matters in small imaging studies, where losing several datasets can materially affect precision.
A connection on a map is a statistical relationship
Functional connectivity usually concerns how measured activity varies together over time. It does not mean that a new anatomical wire has formed between two regions, or establish which region causes the other to change. A colourful line on a brain diagram can make the relationship seem more concrete than the measurement warrants.
The paper combined MRI-based measures with magnetoencephalography, which detects magnetic signals associated with neural activity. Different measurements can constrain an explanation from different directions, but they do not become interchangeable. A change in blood flow, a change in signal correlation and a change in oscillatory power describe different aspects of the system.
The experience is also a measurement
Participants' reports supplied another part of the evidence. Relating an imaging change to hallucination intensity or an altered sense of self can help identify candidate mechanisms. It does not prove that the measured change is sufficient to produce the experience or that all people will respond in the same way.
The placebo comparison and within-person design help separate some sources of variation. They cannot remove every interpretive problem. A conspicuous psychoactive effect can make blinding difficult, while a controlled scanner session differs from many other settings. The paper should therefore be read as a bounded experiment, not a general guarantee about effects, safety or therapeutic benefit.
What the images can support
The finding challenges an overly narrow picture in which visual experience is simply a response to light arriving through the eyes. In this experiment, vivid visual phenomena accompanied changes in distributed brain activity even when external visual input was restricted. That is an interesting association in its own right.
Read the relevant figure legend together with the participant count, measurement type and reported correlation. Then distinguish observation from the authors' proposed explanation. Doing so preserves the study's scientific interest without turning its maps into a complete picture of consciousness. The images show a relationship worth investigating; they do not disclose a hidden visual world independent of the participant's brain.
Sources and further reading
- Neural correlates of the LSD experience revealed by multimodal neuroimaging ↗
PNAS 113(17), 4853–4858; Results, Figures 1–5, Methods; 20 participants and fMRI dataset of 15