Most mental-health medications aim to increase the levels of the neurotransmitters serotonin and dopamine in the brain, however, scientists are now looking more closely into the effects of another neurotransmitter - GABA. GABA (gamma-aminobutyric acid) dampens down brain activity and imbalances in GABA are thought to be involved in some of the runaway thoughts characteristic of bipolar disorder, schizophrenia and anxiety. An inability to stop negative thoughts is also thought to be one of the factors leading to depression and researchers from the Centre for Addiction and Mental Health in Toronto looked into the links between levels of GABA and depression in a study of 85 people. 25 had treatment-resistant depression, 16 had major depression but were taking no medication, 19 had major depression but had been successfully treated and 25 formed a healthy control group. Only in the group who had been unaffected by depression did GABA work normally and the less responsive to medication people were the lower the levels of GABA in their brain were.