Neurobiology of Anxiety Disorders

In recent years, advances in the fields of neuroimaging and experimental psychology increased our understanding of the basic mechanisms of classical conditioning and learning, contributing to our knowledge of the neurobiology of anxiety disorders. Research has shown that the amygdala is the cornerstone of fear circuitry and that abnormalities in amygdala pathways can affect the acquisition and expression of fear conditioning. Activation of the amygdala in response to disorder-relevant stimuli has been observed in anxiety disorders. The roles of the hippocampus, nucleus accumbens, periaqueductal gray, and insular and medial prefrontal cortices in response to fear have been identified as well. Neurotransmitters such as serotonin, dopamine, γ-aminobutyric acid, glutamate, and some neurosteroids play an important part in the neurobiology of anxiety disorders. Neuropeptides such as oxytocin, neuropeptide Y, galanin, and cholecystokinin have been shown to modulate stress response. Drugs such as N-methyl-d-aspartate (NMDA) antagonists and blockers of voltage-gated calcium channels in the amygdala are anxiolytic. Fear extinction, which entails new learning of fear inhibition, is the mechan