ScienceDaily (Dec. 3, 2007) — Why do mental illness and drug addiction so often go together? New research reveals that this type of dual diagnosis may stem from a common cause: developmental changes in the amygdala, a walnut-shaped part of the brain linked to fear, anxiety and other emotions.
Dual diagnosis is common yet difficult to treat. Addiction of all types -- to nicotine, alcohol and drugs -- is often found in people with a wide variety of mental illnesses, including anxiety disorders, unipolar and bipolar depression, schizophrenia, and borderline and other personality disorders. Lead author Andrew Chambers, MD, cites clinical reports that at least half the people who seek help with addiction or mental-health treatment have co-occurring disorders. Epidemiological data says that from two to five of every 10 anxious or depressed people, and from four to eight of every 10 people with schizophrenia, bipolar disorder, or antisocial personality, also have some type of addiction.
To find the scientific basis for this complex, seemingly intractable pairing, which has in the past been attributed to "self-medication," Chambers' team at the Indiana University medical school compared the adult mood- and drug-related behavior of two groups of adult rats: those whose amygdalas were surgically damaged in infancy and those whose amygdalas were left intact but who underwent a sham surgery, to equalize their treatment.