Schizophrenia Daily News Blog

Schizophrenia and Drug Addiction may Co-Occur Due to Disturbance in Part of the Brain

Psychiatric problems often occur comorbidly, or in association with one another. A common comorbid disorder in association with mental illness is drug addiction. It has been hypothesized that this may be because people who suffer from mental illness are more susceptible to drug use and addiction because of their compromised mental state and/or the difficulty they experience in dealing with their illness. A new study further investigated this comorbidity, and found that a connection between mental illness and drug addiction may exist prior to the development of either. Specifically, the study examined rats and found that those with a damaged amygdala at birth were more likely to exhibit adult behavior that was abnormal in relation to fear, as well as, an increased sensitivity to cocaine.

The study will be featured as a part of report published in this month's issue of the journal, Behavioral Neuroscience. The report focuses on the reasons behind the comorbidity of mental illness and drug addiction. It discusses the new research, which finds, as described above, the significance of "developmental changes in the amygdala," linked to the association between mental illness and drug addiction. The amygdala "is a walnut-shaped part of the brain linked to fear, anxiety and other emotions."

Though dual diagnosis of mental illness and addiction is common, it's still something that clinicians find difficult to treat. According to the lead author of the report, Andrew Chambers, MD, "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."

Chambers and his team attempted to study the reason behind the co-occurrence of mental illness and drug addiction by examining the drug and mood behavior of two sets of adult rats. Their two groups of rats consisted of one group where the rats all had amygdalas that had been "surgically damaged in infancy, and" the other group, which consisted of rats "whose amygdalas were left intact but who underwent a sham surgery, to equalize their treatment." The researchers performed their study at the Indiana University Medical School.

Rats with damaged (lesioned) amygdalas grew up abnormally under-responsive to ambiguous or potentially threatening stimuli. Not showing the normal caution, they moved significantly more in response to novelty, showed significantly less fear in an elevated maze, and kept socializing even when exposed to the scent of a predator.

Crucially, these same rats also were significantly more sensitive to cocaine after just one exposure. And rats given repeated cocaine injections later showed even stronger expressions of the enduring changes in behavior – suggesting an overall hypersensitivity to the addictive process.

Chambers and his team conclude that the conditions of or problems with the brain early on may affect a person's susceptibility to drug addiction. In the past, researchers and clinicians thought that the dual diagnosis of mental illness and drug addiction was common because people suffering from mental illness were likely to self-medicate. But Chambers and his research team's findings suggest that the additional diagnosis of drug addiction (to mental illness), may be the result of an increased vulnerability to drugs and not necessarily an attempt to self-medicate.

Chambers encourages all mental-health practitioners and researchers to use insights of each individual disorder (namely, mental illness and drug addiction), to come up with new and more effective treatments for the dual diagnosis. He further states that since these disorders seem to be linked neurobiologically, simultaneous treatments for both disorders may be effective.

Another important point Chambers makes is that of environmental factors and their ability to change or affect preexisting genetic vulnerabilities to mental illness and drug addiction. He states that emotional trauma early in life experienced by someone who already has a genetic vulnerability may change the way in which the "neural networks intrinsic to the amygdala" develop. This may then cause further changes, which then manifest themselves as the comorbid disorders of mental illness and drug addiction in adulthood.

Full Article: Neonatal Amygdala Lesions: Co-Occurring Impact on Social/Fear-Related Behavior and Cocaine Sensitization in Adult Rats. R. Andrew Chambers, et al, Behavioral Neuroscience, Vol 121, No. 6.

Related Reading:
Child and Teen Brains Sensitive to Stress, a Key Factor in Mental Illness
Brain Functioning in Human Behavior