Serotonin is a chemical necessary for communication between nerve cells. It helps to regulate mood and low levels can lead to depression.  Carbohydrate-rich meals may increase serotonin, but everybody is a little different and the effect depends upon other dietary factors.  Your best bet is to experiment with eating different types and amounts of carbohydrate at various times while noting how you feel.  As an alternative, you can follow the Serotonin Power Diet by MIT scientist Judith Wurtman.  The diet consists of 3 meals a day with 3 high carbohydrate, low protein, low fat snacks in-between, phased down to one snack a day over the course of 12 weeks.  Read about it in The Serotonin Power Diet: Use Your Brain's Natural Chemistry to Cut Cravings, Curb Emotional Overeating, and Lose Weight.