Amplitude of low-frequency fluctuations in bipolar disorder: a resting state fMRI study

The spontaneous low frequency fluctuations (LFF) of blood oxygenation level-dependent (BOLD) signal in resting state have been identified as a biological measure of baseline spontaneous activity in the brain. Increasingly, studies of spontaneous resting state functional connectivity have demonstrated neural network abnormalities in bipolar disorder (BD). This study used the amplitude of low frequency fluctuations (ALFF) to explore the regional functional changes in BD during resting state.

Twenty-nine BD participants and 29 matched healthy controls (HC) were recruited to undergo resting-state functional magnetic resonance imaging scan on a 3.0T magnetic resonance imaging system. The ALFF of BOLD signal in gray matter for each participant was calculated, and then was compared between BD and HC using ALFF maps.

Compared to the HC group, the BD group showed increased ALFF in ventral prefrontal cortex, dorsal lateral prefrontal cortex, frontal eye field, insula, and putamen with extension into the ventral striatum, as well as decreased ALFF in the lingual gyrus (p<0.05, corrected).

Although we observed differences in ALFF between BD and HC, we cannot conclusively state that these differences are caused by the pathophysiology of BD since most of BD participants were being treated with medications at the time of scanning.

Our results revealed altered regional brain activity in BD during resting state. The affected regions have been associated with BD pathophysiology. This suggests that methods using ALFF method may potentially be useful in further studies of this disorder.