Delta Wave MRI: fMRI of Electrophysiologic Activity.

We propose a novel application of MR encephalography (MREG) to detect the frequency spectrum of endogenous slow oscillatory brain activity (delta, <4 Hz). MREG offers faster image acquisition than conventional fMRI and superior spatial localization than electroencephalography/magnetoencephalography. MREG was acquired at a 0.1-second temporal resolution in a healthy adult during interleaved wakefulness and sleep to demonstrate its capability for detecting delta-band power changes associated with sleep, previously demonstrated by electroencephalography. For each voxel, the brain activity of MREG signal was used to compute a spectrogram and a whole-brain image of delta-band spectral power. The delta-band power was observed to increase during sleep compared with the awake states using measures from MREG voxelwise spectrograms and sequential whole-brain spatial maps of slow-wave power. This work introduces an MR technique for measuring brain slow-wave activity that is sensitive to changes in the magnitude and frequency of brain activity in sleep.