Here's also an easy summary of it's effect and recommendation If one consider buying supplements:
https://www.reddit.com/r/MushroomSupplements/comments/h090ry...
Bought some myself and tried to track its effect by playing 3DS Devilish Brain Training game and track performance.
I feel like I have less "brain-fog" or rather, brain-fog induced procrastination though. But taking this coincided with a less-stressful time of my life so It might be related to both.
I was pretty bummed, I was hoping for a little boost from this as I had read good things about it, including the NIH articles you posted.
I can also confirm, finding the supplements that are not just mostly the ground brown rice flour is also a little difficult.
I'd made sure t get one that was comprised only of the fruiting bodies, with a tested percentage of polysaccharides.
Here's just another link of some lighter details. https://learn.freshcap.com/tips/myceliated-grain/
The influence of Hericium erinaceus extract on myelination process in vitro https://pubmed.ncbi.nlm.nih.gov/12675022/
Neurohealth Properties of Hericium erinaceus Mycelia Enriched with Erinacines https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5987239/
Protip: If/When buying supplements -- There's many that are just selling capsules of ground myceliated brf (brown rice flour - the substrate inoculated/grown on). Mycelium is the 'roots/pre fruiting stage' of the fungi -- The fruit body/ mushroom itself has much greater concentrations of the desired compounds.