Substance abuse by psychiatric inpatients correlated with significantly increased interhemispheric connectivity in two frontal brain areas, the insula and the inferior frontal gyri, according to a case-control study published Jan. 12 in Neuropharmacology.
The results add to evidence linking the insula and the inferior frontal gyri (iFG) with substance abuse disorders (SUD), said Humsini Viswanath at Baylor College of Medicine, Houston, and her coauthors. “We postulate that specific drugs of abuse act upon anatomic, metabolic, or molecular pathways in the insula and iFG, resulting in the observed changes in functional and structural connectivity,” the investigators wrote.
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Abuse of tobacco, alcohol, cocaine, sedatives, and hallucinogens was linked with increased resting state functional connectivity (RSFC) of the insula, while use of amphetamines and inhalants correlated with increased RSFC of the iFG, the researchers said. Use of cannabinoids and opiates did not correlate with brain connectivity in either structure, they added (Neuropharmacology 2015 Jan. 12 [doi:10.1016/j.neuropharm.2014.12.030]).
Substance abuse disorders are the leading cause of death among individuals with psychiatric disorders, but studies of mental illness often exclude patients with comorbid SUD, the investigators noted. They therefore used diffusion tensor and RSFC imaging to compare 151 psychiatric inpatients with and without concurrent SUDs, as determined by the World Health Organization Alcohol, Smoking, and Substance Involvement Screening Test (WHOA).
About the same proportion of patients with and without SUDs had depression (38% vs. 40%, respectively), anxiety disorders (50% vs. 53%), bipolar disorders (17% vs. 14%), and personality disorders (41% vs. 37%). But patients with SUDs had increased interhemispheric RSFC for the insula (P < .001) and inferior frontal gyrus (P < .05) and had significantly smaller right inferior frontal gyri, compared with psychiatric inpatients without comorbid SUD, they reported.
Studies of heterogeneous groups of patients “can reveal significant changes in brain structure and function, even in highly comorbid samples,” concluded Ms. Viswanath and her associates. “As additional patients are recruited to this cohort for future studies, we expect to identify even more fine-grained relationships between specific drugs of abuse and brain structure, function, and connectivity in psychiatric conditions.”
The research was supported by the McNair Medical Institute, the Menninger Clinic, the department of psychiatry at Baylor College of Medicine, the National Institutes of Health, and the Brain & Behavior Research Foundation. The researchers declared no financial conflicts.