Revisiting claims of extracranial biophoton detection from the human brain

TL;DR

This paper critically evaluates claims of extracranial biophoton detection from the human brain, highlighting methodological issues and emphasizing the need for careful experimental design.

Contribution

It challenges previous interpretations of brain UPE measurements, clarifying the limitations of current detection methods and the dominance of background signals.

Findings

UPE from the head is much weaker than previously reported.

Background light dominates signals in reported studies.

Photon attenuation by scalp and skull affects detection accuracy.

Abstract

Ultraweak photon emission is the spontaneous emission of extremely low levels of light from a broad range of biological systems. Recent studies have reported that UPE measured extracranially can serve as a potential non-invasive biomarker of brain activity. Here, we show that this interpretation suffers from serious problems. First, when observed under properly dark conditions, the UPE from the head is much weaker than what is reported in certain papers on 'brain UPE' from human heads. Signals detected in these studies are overwhelmingly dominated by background light. Second, photons at wavelengths < 600 nm are strongly attenuated by scalp and skull tissues, and longer wavelengths fall largely outside the effective spectral sensitivity of the photomultiplier tubes (PMTs) used. As a consequence, even if UPE from the head is detected under properly background-free conditions, it is likely to be dominated by emission from the scalp rather than from the brain, certainly as long as PMTs are used. Our results emphasize the importance of careful experimental design to make genuine progress on this important question.