I only have marginal knowledge about neuroscience, but one of my neuroscience professors in class would tell us

"You can cure anything in mice."

I don't know the mechanism why, but you can find tons of papers with incredibly strong results for curing of mitigating dementia, cognitive decline, addiction, etc in mice, but these almost never seen to work on people.

I've long regarded the great variety of chilis as its own distinct food group. But wonderful as they are for flavoring food, quite often in my home, I'm not sure how much of an effect orally consumed capsaicin has on memory functioning.

Conceivably parenteral capsaicin has different effects on hippocampal integrity or physiology than achievable with ingestion. I'm not familiar enough with disposition of capsaicin in the gut to comment further. My question is whether capsaicin passes from gut into the circulation in any appreciable quantity. I suspect it doesn't but I couldn't say I know for sure. I'll have to add it to the already long list of things I need to look up.

> What's really cool is that the paper used low-dose capsaicin (just 5 μg/kg injected), and it completely restored hippocampal FOS activity and memory in older mice.

There are countless papers published where simple ingredients produce miracles in mice. Most of them don’t replicate.

If you look up most food ingredients you can find someone, somewhere claiming to have used it to produce amazing outcomes in mice. After you read a lot of those you learn not to take individual papers seriously if the claims seem too good to be true.