Controversy over Hippocampal Volume
The hippocampus of the brain was found to be considerably smaller in obsessive-compulsive patients – people with recurring thoughts, images or impulses that impinge on daily life. Researchers from the NIMHANS, Bengaluru noted that this was observed in patients under medication and with depressive symptoms. They felt that there was a need to remove these confounding variables that may have influenced the finding.
So, Janardhanan C. Narayanaswamy and team, from the NIMHANS, decided to investigate the relationship between hippocampal volume and the clinical correlation in obsessive compulsive patients not under medication. The study was approved by their ethics committee.
The scientists enrolled twenty six medication-naive patients at their specialty OCD clinic with twenty matched healthy controls and made all participants sign written informed consent.
The team used the Mini International Neuropsychiatric Interview for diagnosis. They evaluated the patients with the Yale-Brown Obsessive-Compulsive Scale to assess severity and type of OCD.
After screening the patients for potential contraindications, they used magnetic resonance imaging to assess the volume of the hippocampus. With 3 D slicer software, they manually delineated the posterior and anterior hippocampus. Besides differences between left and right hippocampus volumes, the researchers analysed differences between the posterior and anterior divisions of the hippocampus. In their analysis, they included intracranial volume as covariate since the differences in individual patient brain size can confound results.
In contradiction to earlier reports, the scientists found that the left hippocampal volume was considerably higher in OCD patients than in healthy controls!
However, the severity of the compulsion score by the Yale-Brown Obsessive-Compulsive Scale and the volume of the posterior part of the left hippocampus correlated negatively in OCD patients.
Thus, though increased hippocampal volume can be a marker for the illness, as the disease becomes severe, the left posterior hippocampus is seen to reduce in size.
The hippocampus takes care of spatio-temporal navigation and higher volume may have a role in the tendency of patients to double check everything in their path, one of the symptoms of OCD.
The reduction in the volume of the left posterior hypothalamus, in severe cases of OCD, may be related to medication and other associated morbidities, such as depression, social avoidance and anxiety, say the researchers.
J. Affect. Disord., 236: 1-5 (2018); DOI: 10.1016/j.jad.2018.04.048
Pallavi Deshpande, Assistant Manager-Scientific Affairs, Indus Biotech Pvt Ltd.