Abnormalities in the circuitry of the prefrontal cortex can contribute to impairments in working memory, though in only a specific subsection of GABA neurons. Local circuit neurons regulating these types of functions in the prefrontal cortex show altered GABA neurotransmission. There was also reduced mRNA expression (below the level of detection) of glutamate decarboxylase (GAD₆₇), which is an enzyme responsible for making GABA in the prefrontal cortex, and GABA membrane transporter-1 (GAT-1) - which is seen in 25-35% of GABA neurons in the prefrontal corteces of those with schizophrenia.