Brain Center May Link Addiction, Mental Illness

FRIDAY, Dec. 21 (HealthDay News) -- Developmental problemsinvolving a walnut-shaped part of the brain called the amygdala -- linkedto fear, anxiety and other emotions -- may explain why mental illness andaddiction often appear together, researchers say.
Many kinds of addiction -- such as those for alcohol, drugs andnicotine -- occur in people with various kinds of mental illness,including depression, schizophrenia and anxiety disorders, according tobackground information in an American Psychological Association newsrelease about the Indiana University study.
Two to five of every 10 anxious or depressed people, and four to eightof every 10 people with schizophrenia, biopolar disorder or antisocialpersonality, also have some form of addiction, according toepidemiological data.
In this study, published in the December issue of BehavioralNeuroscience, the researchers compared the behavior of adult ratswhose amygdalas were surgically damaged in infancy and adult rats withintact amygdalas.
Rats with the damaged amygdalas showed less fear and caution thannormal and were significantly more sensitive to cocaine after just oneexposure to the drug. Rats with damaged amygdalas that received repeatedcocaine injections developed "even stronger expressions of the enduringchanges in behavior -- suggesting an overall hypersensitivity to theaddictive process," the researchers noted.
Since both groups of rats were raised in the same controlledconditions, the damaged amygdala was the likely cause of the impaired fearbehavior, as well as the heightened drug response, in the one group ofrats, the study authors concluded.
In humans, disease and interactions between genetic and environmentalfactors can alter amygdala function or change the way it's connected tothe rest of the brain during childhood and adolescence.
"Early emotional trauma, paired with a certain genetic background, mayalter the early development of neural networks intrinsic to the amygdala,resulting in a cascade of brain effects and functional changes thatpresent in adulthood as a dual-diagnosis disorder," lead author Dr. AndrewChambers explained in a prepared