A study on serotonin, a mood-regulating molecule in the brain that regulates many brain synapses, is helping to unravel the puzzle surrounding its role in autism. The activity and regulation of the serotonin transporter (SERT), protein is critically dependent on a number of other proteins that tell the protein where to locate on nerve cells and how to act. Shifts in the transporter’s activity can significantly impact the ability of serotonin to act in the brain.