  Given that many fundamental questions in neuroscience are still open, it
seems pertinent to explore whether the brain might use other physical
modalities than the ones that have been discovered so far. In particular it is
well established that neurons can emit photons, which prompts the question
whether these biophotons could serve as signals between neurons, in addition to
the well-known electro-chemical signals. For such communication to be targeted,
the photons would need to travel in waveguides. Here we show, based on detailed
theoretical modeling, that myelinated axons could serve as photonic waveguides,
taking into account realistic optical imperfections. We propose experiments,
both \textit{in vivo} and \textit{in vitro}, to test our hypothesis. We discuss
the implications of our results, including the question whether photons could
mediate long-range quantum entanglement in the brain.
