People with schizophrenia may have abnormal regulation of certain chemicals (neurotransmitters) in the brain, related to specific pathways or "circuits" of nerve cells that affect thinking and behavior. Different brain circuits form networks for communication throughout the brain. Scientists think that problems with how these circuits operate may result from trouble with certain receptors on nerve cells for key neurotransmitters (like glutamate, GABA, or dopamine), or with other cells in the nervous system (called "glia") that provide support to nerve cells within brain circuits. The illness is not believed to be simply a deficiency or "imbalance" of brain chemicals, as was once thought.