Patients with established bipolar I disorder show reductions in superior temporal gyrus (STG) gray matter volume, especially in the left posterior regions, relative to mentally healthy controls, results of a magnetic resonance imaging (MRI) study show.

Among the patients, daily lithium dose was positively correlated with gray matter volume in the right STG, suggesting it has a neuroprotective effect preventing reductions in this particular region.

“In addition to mood instability, patients with bipolar disorder appear to have subtle cognitive compromise that may be underpinned by both structural and functional changes identifiable using modern neuroimaging techniques,” Tsutomu Takahashi (Melbourne Neuropsychiatry Centre, Victoria, Australia) and colleagues comment in the Journal of Affective Disorders.

One region of interest, the STG, contains the primary auditory cortex (heschl gyrus [HG]) and auditory association cortex (planum temporale [PT] / planum polare [PP]), while its lateral portion plays a crucial role in emotional processing and social cognition.

In the present study the researchers used MRI to examine STG volume and its gray matter subregions ??” PP, HG, PT, and lateral STG (rostral and caudal regions) ??” in 26 patients with established bipolar I disorder and 24 age and gender-matched mentally healthy controls.

The patients with bipolar disorder had significantly smaller volumes in the left PT and left caudal STG compared with mentally healthy controls, although STG white matter volume did not differ between the groups - which likely reflects normal myelin and axon density.

Age was negatively correlated with all STG gray matter subregion volumes in the bipolar disorder patients and controls. Of note, this correlation was significantly stronger in the patients than in controls for the left HG.

Among the bipolar disorder patients, illness duration was negatively correlated with left HG volume, but this correlation was not significant after controlling for age.

The number of manic/depressive episodes and daily dosage of valproate did not correlate with any STG volumes. But daily dosage of lithium treatment at the time of scanning was significantly positively correlated with right PP and right rostral STG.

“The effect of medication is an important consideration … lithium could reverse or prevent gray matter abnormalities including the STG region in bipolar disorder patients by its neurotrophic/neuroprotective effects,” Takahashi et al comment.

The researchers say their findings clearly “implicate STG gray matter in the pathophysiology of bipolar disorder,” but call for longitudinal studies to examine the nature of the STG changes.

MedWire (www.medwire-news.md) is an independent clinical news service provided by Current Medicine Group, a trading division of Springer Healthcare Limited. © Springer Healthcare Ltd; 2010

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