The most widely studied behavioral model of fear is classical fear conditioning as it may be assessed across many different species, including humans. Conflicting signals can be divided in two basic categories: emotional and non-emotional. Cortical control of anxiety appears to be especially important in the presence of emotional stimuli. Human brain imaging studies have found insular abnormalities in anxiety patients. Patients with panic disorders display decreased gamma-aminobutyric acid (GABA A)/benzodiazepine sites in the insular cortex, while phobic patients show an increase in insular activity during the presentation of fearful faces. Serotonin plays an important role in the regulation of emotions, including anxiety, fear, and depression. The complex and important role that the serotonergic system plays in emotional regulation is also unambiguous. Serotonergic modulation occurs via interaction with a wealth of receptors with complementary and sometimes opposite effects acting at different levels in the circuitry underlying anxiety.