Here’s a new journal article from the Journal of Alzheimer’s Disease. I’m a co-author, but don’t let that get in the way.
This article looks at the animal and clinical evidence for the use of transcranial and intracranial red and near infrared light devices. There is a lot of detailed information, including and in-depth description of the effect of transcranial red and near infrared lights in people with Parkinson’s disease.
As for which is best – intracranial or transcranial? The verdict is that neither is best on its own. The best is having both working together. It makes sense, having light shining from inside and outside the brain.
Alas, you might be waiting a while before you get access to an intracranial light implant (think DBS with a 670nm LED light), but you can use transcranial lights right now. You can make your own (instructions are here) or look at the Duo Coronet (link is here) .
Johnstone DM, Hamilton C, Gordon LC, Moro C, Torres N, Nicklason F, Stone J, Benabid AL, Mitrofanis J. Exploring the Use of Intracranial and Extracranial (Remote) Photobiomodulation Devices in Parkinson’s Disease: A Comparison of Direct and Indirect Systemic Stimulations. J Alzheimers Dis. 2021;83(4):1399-1413. doi: 10.3233/JAD-210052. PMID: 33843683.
I can understand the skepticism about the biological effect of red lights, because that’s where I started from. It seemed too good to be true. However, there is a wealth of excellent quality research out there, and the evidence is compelling that red and near infrared lights protect existing neurones, and can stimulate new neurones to be created, stimulate blood vessels to increase connections- neuroprotection, neurogenesis and angiogenesis.