Amplitude of low frequency fluctuation within visual areas revealed by resting-state functional MRI.

Most studies of resting-state functional magnetic resonance imaging (fMRI) have applied the temporal correlation in the time courses to investigate the functional connectivity between brain regions. Alternatively, the power of low frequency fluctuation (LFF) may also be used as a biomarker to assess spontaneous activity. The purpose of the current study is to evaluate whether the amplitude of the LFF (ALFF) relates to cerebral physiological states. Ten healthy subjects underwent four resting-state fMRI scanning sessions, two for eyes-open (EO) and two for eyes-closed (EC) conditions, with two sets of parameters (TR=400 ms and 2 s, respectively). After data preprocessing, ALFF was obtained by calculating the square root of the power spectrum in the frequency range of 0.01-0.08 Hz. Our results showed that the ALFF in EO was significantly higher than that in EC (P<0.05, corrected) in the bilateral visual cortices. Furthermore, the ALFF in EO was significantly reduced in the right paracentral lobule (PCL) than in EC (P<0.05, corrected). Region of interest (ROI) analysis showed that the ALFF differences between EO and EC were consistent for each subject. In contrast, no significant ALFF differences were found between EO and EC (P<0.381) in the posterior cingulate cortex. All these results agree well with previous studies comparing EO and EC states. Our finding of the distinct ALFF difference between EO and EC in the visual cortex implies that the ALFF may be a novel biomarker for physiological states of the brain.