Depleting brain serotonin by reducing tryptophan availability leads to increased impulsivity and short-term gratification.

“where they've taken normal people and depleted their serotonin by giving them a shake of Branch chain amino acids like Lucine and isol leucine which out compete tryptophan to be transported into the brain so what happens is after you give someone a big Shake of these branching amino acids without tryptophan their tryptophan levels drop in their brain and subsequently their serotonin levels drop by about 90% And what happens is people become very impulsive their short-term uh thing their short-term gratification kicks in”