This paper seems to be saying that externally impressed ~40 Hz stimulation helps mitigate the pathology of diseased brains. But I don't think it's quite correct for the general review to call it "promoting brain health". The cellular pathology is still there. The functionality of the brain is just being augmented.

Reports of improved performance with this 40 Hz brain stimulation being agumented is not surprising given the biological origin of this 40 Hz EEG observable correlating with the switching of the thalamo-cortical loops that are necessary for (but not sufficient for) self-reporting of "conscious" state in humans.

It may be these thalamo-cortical neuronal populations are getting a bit of help getting over the hump from the auditory cortices thalamocortical loops to get those action potentials going like they used to.

the study cites Alzheimers and "other neurological conditions" - curious how broad that is and whether this could be of use for the average middle age person who's not quite as sharp as they once were, ahem, me.

I thought gamma rays had a much higher frequency.