Eye movement study supports cerebellar involvement in bipolar disorder
MedWire News: Results from a US study of smooth pursuit eye movements (SPEMs) in bipolar disorder patients provide further evidence for cerebellar involvement in the mood disorder.
Writing in the Journal of Psychiatric Research, Laura Frances Martin (University of Colorado Denver School of Medicine) and colleagues observe that previous studies have found SPEMs to be abnormal in patients with schizophrenia and bipolar disorder.
They explain: "Functional imaging methods have revealed greater hippocampal activity and less frontotemporal, visual, and posterior cerebellar activity in individuals with schizophrenia when performing a SPEM task."
However, they add: "The underlying neurobiology of SPEM deficits in bipolar disorder is unknown."
To investigate, the team studied 14 patients with bipolar disorder and 14 mentally healthy individuals (controls) who were aged a mean of 34 and 36 years, respectively.
All of the participants underwent functional magnetic resonance imaging of the brain while performing a SPEM task. This involved patients watching a white dot that moved horizontally back and forth across a screen with a 700-msec fixation period at each edge. During the rest condition, patients were instructed to look straight ahead at a blank screen. The smooth pursuit and rest conditions lasted for 20 seconds each and were presented four times in an alternating block design for each run. Patients performed two runs.
The researchers found that the bipolar disorder patients showed significantly greater activation of cerebellar vermis, specifically lobule 9 (uvula), than controls during the SPEM task.
There were no significant differences between the two groups regarding activity in other regions of interest, including the hippocampus.
Blood oxygenation level-dependent (BOLD) responses were positively correlated with depressive symptoms, as assessed using the Beck Depression Inventory, on the day of testing in the bipolar disorder patients, the researchers note.
However, there were no associations between BOLD response and Young Mania Rating Scale or Positive and Negative Syndrome Scale total or subscale scores in the bipolar disorder patients.
Martin and team conclude: "The finding of abnormally increased cerebellar vermis hemodynamic response in bipolar disorder adds support to a growing body of evidence for the presence of cerebellar vermis abnormalities in bipolar disorder."
They add: "This abnormality in the vermis may either contribute to impaired coordination of affective responses or represent a compensatory response to control aberrant affective responses.
"Future studies establishing a temporal relationship between affective disturbance, medication effect and vermis activity levels, as well as the specificity of this finding to bipolar disorder, are needed."
MedWire (www.medwire-news.md) is an independent clinical news service provided by Springer Healthcare Limited. © Springer Healthcare Ltd; 2011
By Mark Cowen