[ghotli]

An actual expert can fact check me but as far as I'm aware that's due to how magnesium sits within binding site within the NMDA receptor ion channel as a blocking / gating factor. If supplementation actually raises the level of available magnesium beyond the blood brain barrier (when you're perhaps in need of some) then it would affect the way in which that ion channel affects the downstream excitatory effects towards long term potentiation.