Ginkgo also known as the Maidenhair Tree after Adiantum is a unique species of tree with no close living relatives. Extracts of Ginkgo leaves contain flavonoid glycosides and terpenoids (ginkgolides, bilobalides) and have been used pharmaceutically. Ginkgo supplements are usually taken in the range of 40–200 mg per day. Recently, careful clinical trials have shown Ginkgo to be ineffective in treating dementia or preventing the onset of Alzheimer's Disease in normal people.
Recent study about Ginkgo biloba published in Brain Research journal evaluated evaluated the effects of acute (one dose)or subacute treatments (one daily dose/seven days) with EGb 761 (0.5 g kg−1 and 1.0 g kg−1) onrats submitted to a conditioned emotional response (CER) in comparison with positive (4 mg
kg−1 Diazepam) and negative (12%Tween 80) control groups.
You can read the full article in brain research journal 29 December 2008