Gamma-aminobutyric acid or GABA is the most important inhibitory neurotransmitter in the brain. Inhibitory neurotransmitters protect against overstimulation of the brain, which is important for mood, sleep, brain function and mental health. GABA is effective in reducing stress and apprehension, and promotes healthy sleep. It is effective against a variety of central nervous system disorders, and has been shown to affect the brain directly, increasing alpha-brain waves (those associated with relaxation) and reducing beta-brain waves (those associated with worry and stress). During times of stress, GABA acts to regulate brain excitability, acting as an inhibitor of nerve impulses or signals between neurons in the brain and spinal cord, effectively creating a "calming effect".