This MRI image shows the increased size of the thalamus in a child with OCD.

A Wayne State University study has demonstrated how medication can directly impact the size of a child’s brain.

David Rosenberg, MD, associate professor of psychiatry and behavioral neurosciences, and WSU alum, Andrew Gilbert, who is now a first-year psychiatry resident, studied 42 subjects, half of whom were healthy and half of whom were children with obsessive compulsive disorder (OCD) who had never been treated for it. Using magnetic resonance imaging (MRI), the doctors discovered that the thalamus, a part of the brain that relays motor and sensory impulses, was larger in children with OCD.

But, after 12 weeks of treatment with paroxetine, an anti-depressant also known as Paxil, the size of the thalamus decreased to the same size as those seen in healthy children. This decrease was robustly associated with improvement in OCD symptoms. Bigger thalamus size before treatment predicted better response to medication.

“A concern of parents, doctors and clinicians is the impact of medication on a child’s brain,” Dr. Rosenberg said. “Here we provide the first-ever demonstration that medication treatment can affect the size of a child’s brain. This is very exciting in children who have brain abnormalities that can normalize.”

The thalamus has high levels of serotonin, a neurotransmitter most implicated as part of the cause of OCD. Serotonin helps nerve cells send signals to one another. When serotonin is released from one cell and travels to another, it can be absorbed into the receiver cell or reabsorbed back in the sender cell. Anti-depressants used to treat OCD block serotonin from being reabsorbed by sender cells. These drugs, which are also used to treat depression and other disorders, are known as serotonin reuptake inhibitors. Paroxetine, the drug used in the study that appeared to reduce the size of the thalamus, is part of this class of drugs.

The study underscores the need for further research to determine the impact of medication on the developing brain. Future studies could show that other neuropsychiatric conditions, such as depression, bipolar disorder, attention deficit disorder and schizophrenia, could be associated with brain abnormalities that are not evident using standard diagnostic tools, but are with advanced imaging tools.

Dr. Rosenberg’s study on OCD and the thalamus was published in the May issue of the American Medical Association journal, The Archives of General Psychiatry.