Spectral content of the ongoing bold fMRI activity is modulated by resting state-type

Background: In functional imaging, activations are defined against a resting state of eyes closed, eyes open, or maintained fixation. It has become clear that baseline BOLD signals display periodic fluctuations. Furthermore, it is well known that ongoing neural activity in the resting state is modulated by state-type. Specifically the spectra of alpha band EEG/MEG signals are modulated by resting state-type [1]. This abstract reports effects of state-type on the spectral content of ongoing fMRI BOLD activity. Methods: Ten subjects participated in a BOLD fMRI experiment comprised of nine 5.5 minute runs: 3 eyes open, 3 eyes closed, 3 fixation. A general linear model was fit to each subject's detrended data. Regressors included a constant term and cosinusoids modeling frequencies from one full cycle to the Nyquist limit. For each subject, root mean square amplitude power was computed for each frequency and entered into a group analysis: voxel-wise repeated measures ANOVA with random factor subject and fixed factors frequency and state-type. The voxel-wise main effects (frequency, state-type) and interaction were corrected for multiple comparisons [2]. Results: The voxel-wise main effect of frequency showed the spectra of the entire brain to be nonwhite, replicating a known BOLD phenomenon. The main effect of state-type highlighted a subset of regions found within the state-type by frequency interaction, thus we report the latter. Regions whose spectra were modulated by state-type were found in primary sensorymotor cortex, striate and extrastriate visual cortex, auditory cortex, and parahippocampal areas (Figure 1). Across all regions, the eyes closed condition was associated with greater modulation of the ongoing BOLD signal than eyes open and fixation conditions in three frequency bands: 0.006-0.02 Hz, 0.02-0.035 Hz, and 0.035-0.045Hz. Representative spectra shown in Figure 2. Conclusions: The power spectrum of ongoing BOLD activity shows significant effects of resting state-type. Furthermore, these effects are similar to effects of state-type on the spectra of alpha band EEG/MEG signals [1]. This suggests a possible electrophysiological correlate of ongoing resting state BOLD activity. Regions with significant effects of frequency and state-type on the amplitude of the ongoing BOLD signal were limited to early sensory, motor regions and limbic structures. Ongoing activity in higher order regions was not significantly modulated by resting state-type.