Researchers at the University of Glasgow have, for the first time, detected photons traveling entirely through an adult human head—from one side to the other—using powerful lasers and ultra-sensitive detectors.

Until now, non-invasive optical imaging methods like fNIRS could only penetrate about 4 cm into brain tissue. This new work suggests that, under very controlled conditions, light can traverse deep brain structures.

Key points:

• Requires 30 minutes of data collection, no hair, and fair skin to get a signal.
• Computer simulations show that certain brain regions—such as cerebrospinal fluid spaces—guide light along preferred paths.
• Still a proof-of-concept, but it pushes the boundaries of what we thought possible for optical imaging depth.

Takeaway: This is a milestone in optical brain imaging. It doesn’t give us detailed maps of neurons or memories, but it shows there’s more room for improvement in non-invasive brain scanning than previously believed. Incremental advances like this could enable new research tools and diagnostics long before we ever tackle speculative technologies like mind emulation.

Could this eventually lead to more practical, deep-brain scanning methods—perhaps even portable ones?

More information: Jack Radford et al, Photon transport through the entire adult human head, Neurophotonics (2025). DOI: 10.1117/1.NPh.12.2.025014