A structural magnetic resonance imaging studyof the parietal lobe in bipolar disorder

Title: A structural magnetic resonance imaging study of the parietal lobe in bipolar disorder Background: Little attention has been given to the parietal lobe (PL) in brain imaging literature, compared to other brain regions. Despite that, PL has been shown to be involved in several neurocognitive processes (i.e. attention, motor planning and control, emotion regulation), which seem to be impaired in schizophrenia and, with a minor extent, in bipolar disorder (BD). Also, some studies highlighted the presence of structural PL abnormalities in these disorders, thus suggesting PL as a region of interest for a better understanding of BD. Objectives: The aim of this study was to assess PL volumes in BD and to explore volumes change over time, by means of structural Magnetic Resonance Imaging (sMRI). Also, our aim was to investigate the relationships between PL anatomy and socio-demographic and clinical variables, in order to clarify the role of PL as part of a more extended brain network possibly sustaining BD symptomathology. This research was part of the FIRST study (Following Imaging Resilience features in Schizophrenia and affecTive disorder). Methods: A sample of patients with a DSM-IV diagnosis of BD was selected through the South Verona Psychiatric Case Register. A group of healthy volunteers was also recruited. All subjects who met criteria for the study underwent sMRI, along with a clinical assessment composed by rating scales measuring global functioning and psychopathological dimensions. Socio-demographic and clinical variables (i.e. age of onset, number of hospitalization, psychopharmacological treatment) were also collected from patients’ interview and medical records. Results: Forty-six BD patients and 47 healthy controls (HC) (comparable for gender and age) underwent sMRI. Twenty-two BD patients and 16 HC repeated MRI at 1-year follow up. PL was manually traced bilaterally in the sagittal plane (Brains2 software), and grey (GM) and white matter (WM) volumes were calculated. Cross sectional comparison of BD patients and controls showed a statistically significant reduction on bilateral PL GM and WM (left GM p=0.019; right GM p=0.034; left WM p=0.000, right WM p=0.001) in BD patients, compared to healthy subjects. In the longitudinal analysis, a significant group effect on bilateral WM PL (left WM p=0.007, right WM P=0.026) was observed, along with a time effect on bilateral PL GM (left GM p=0.023; right GM p=0.017. No significant interaction effect of time x group was observed (p>0.05). Correlation analyses showed an inverse and significant correlation between bilateral PL WM and GM and length of illness (left PL WM p= 0.001, right PL WM p= 0.002, left PL GM p= 0.001, right PL GM p= 0.001) and between left and right PL WM and Hamilton Depression Rating Scale (HDRS) scores (left PL WM p= 0.002, right PL WM p=0.004) in patients’ group. Moreover, left PL WM positively correlated with Global Assessment of Functioning (GAF) score (p=0.004). Conclusion: Results showed a significant reduction in PL volumes (GM, WM) in patients with BD, compared to HC. No group x time interaction was observed in the longitudinal analysis. Furthermore, PL volumes reduction appears to be associated with severity of depression (HDRS) but also with chronicity and global functioning.