Illustration of the neurocircuitry involved in the response to rewarding stimuli, including drugs of abuse and novelty. Dopamine (DA) plays a key role in this system, through excitatory projections directly connecting the ventral tegmental area (VTA) with the nucleus accumbens (NAc) and prefrontal cortex (PFC). Other excitatory neurotransmitters include glutamate (Ahmadi et al.), serotonin (5-HT), opioid peptides (OP), and acetylcholine (ACh). A major inhibitory neurotransmitter of this reward system is GABA, connecting the VTA, NAc, PFC, thalamus, and ventral palladium. Other brain regions implicated in the response to rewarding stimuli include the hippocampus, amygdala, raphe nuclei, striatum, and arcuate nucleus.