The cause of ADHD is not know, an imbalance of certain neurotransmitters (any of several chemical substances, that transmit nerve impulses across a synapse to a postsynaptic element, as another nerve, muscle, or gland), is believed to be the mechanism behind its symptoms. the result showed that the rate at which the brain uses glucose, its main engery source, was lower in persons with ADHD, like attention, handwriting, motor control, and inhibition responses.