Hi, I am Dr. Michael Murray. Phosphatidylserine or PS for short is the major fatty substance in the human brain.  It plays a major role in determining the integrity and fluidity of cell membranes. Without sufficient levels of PS, brain cells do not transmit the nerve impulse properly.  Normally the brain can manufacture all of the PS it requires, but there is evidence that insufficient production in the elderly is linked to depression, poor memory, and impaired mental function. Good clinical results have been obtained in numerous double-blind studies with PS. The typical dosage is 300 mg daily