>> What else can I consume to improve my brain function except salt and low dose lithium?

Try glycine - 1 gram minimum per day. You may be able to find it as Magnesium Glycinate sold strictly as a Mg supplement. The thing is it contains 6-7 time more Glycine that Mg. so if you take 200mg of Magnesium in this form you'll get about 1.3 grams of glycine. It's a neurotransmitter and helps sleep among other things.