Abnormalities of Cortical Thickness in Bipolar Disorder With Auditory Hallucinations
The findings could be related to differences between the underlying pathophysiological mechanisms of auditory hallucinations in bipolar disorder vs schizophrenia.
Patients with bipolar disorder and a lifetime history of auditory hallucinations were found to have cortical thickness abnormalities in both the left Heschl's gyrus and the superior parietal lobule, according to a recent study published in Bipolar Disorders.
The study investigators initially hypothesized that patients with bipolar disorder and a lifetime history of auditory hallucinations (BD+) would show a thinner cortex in regions of the auditory cortex (Heschl's gyrus, superior temporal gyrus, and planum temporale) than patients with bipolar disorder but without a lifetime history of auditory hallucinations (BD-). This hypothesis was based on previous findings that patients with schizophrenia and a lifetime history of auditory hallucinations had a thinner cortex of the left Heschl's gyrus than patients with schizophrenia without such a history.
Contrary to expectations, the study found a thicker, not thinner, cortex of the left Heschl's gyrus among BP+ patients compared with BP- patients. Additionally, BD+ patients also showed a thicker cortex in the left superior parietal lobule. The differences in cortical thickness could not be explained by global functioning, duration of illness, bipolar subtype, IQ, or the use of psychotropic medications.
These unexpected findings could be related to differences between the underlying pathophysiological mechanisms of auditory hallucinations that cause bipolar disorder patients to only experience auditory hallucinations during mood episodes, and schizophrenia patients to experience them more persistently.
The study sample included 157 patients with bipolar disorder and 279 healthy controls, all between 18 and 65 years of age, and all recruited from outpatient clinics and psychiatric departments in the Oslo region of Norway. It is the first published study of brain structure comparisons of patients with bipolar disorder with and without a history of auditory hallucinations. Participants were first clinically assessed by trained physicians or psychologists to determine global functioning and current depressive, manic, and psychotic symptoms. Participant use of antidepressant, mood-stabilizing, and antipsychotic medications was determined at the same time as participants underwent magnetic resonance imaging (MRI) scans. Version 5.3.0 of the FreeSurfer software package was used to obtain measurements of cortical surface area and cortical thickness.
Study limitations do apply, including the median time gap of 107 days between clinical assessments and MRI scanning and the limited sample size.
Study investigators conclude, “Our study contributes to the current state of research on auditory hallucinations in BD, being the first study to investigate cortical thickness and surface area in association with auditory hallucinations in BD, but replications are needed.”
Mørch-Johnsen L, Nerland S, Jørgensen KN, et al. Cortical thickness abnormalities in bipolar disorder patients with a lifetime history of auditory hallucinations [published online February 13, 2018]. Bipolar Disord. doi: 10.1111/bdi.12627