Spontaneous cerebral hemodynamic oscillations below 100 mHz reflect the level of cerebral activity, modulate
hemodynamic responses to tasks and stimuli, and may aid in detecting various pathologies of the brain. Near-infrared
spectroscopy (NIRS) is ideally suited for both measuring spontaneous hemodynamic oscillations and monitoring sleep,
but little research has been performed to combine these two applications. We analyzed 30 all-night NIRS-electroencephalography (EEG) sleep recordings to investigate spontaneous hemodynamic activity relative to sleep stages
determined by polysomnography.
Signal power of hemodynamic oscillations in the low-frequency (LF, 40-150 mHz) and very-low-frequency (VLF, 3-40
mHz) bands decreased in slow-wave sleep (SWS) compared to light sleep (LS) and rapid-eye-movement (REM) sleep.
No statistically significant (p < 0.05) differences in oscillation power between LS and REM were observed. However,
the period of VLF oscillations around 8 mHz increased in REM sleep in line with earlier studies with other modalities.
These results increase our knowledge of the physiology of sleep, complement EEG data, and demonstrate the
applicability of NIRS to studying spontaneous hemodynamic fluctuations during sleep.
The objective of the study was to assess the usability of a near-infrared spectroscopy (NIRS) device in multimodal
measurements. We combined NIRS with electroencephalography (EEG) to record hemodynamic responses and evoked
potentials simultaneously, and with transcranial magnetic stimulation (TMS) to investigate hemodynamic responses to
repetitive TMS (rTMS). Hemodynamic responses and visual evoked potentials (VEPs) to 3, 6, and 12 s stimuli
consisting of pattern-reversing checkerboards were successfully recorded in the NIRS/EEG measurement, and ipsi- and
contralateral hemodynamic responses to 0.5, 1, and 2 Hz rTMS in the NIRS/TMS measurement. In the NIRS/EEG
measurements, the amplitudes of the hemodynamic responses increased from 3- to 6-s stimulus, but not from 6- to 12-s
stimulus, and the VEPs showed peaks N75, P100, and N135. In the NIRS/TMS measurements, the 2-Hz stimulus
produced the strongest hemodynamic responses compared to the 0.5- and 1-Hz stimuli. In two subjects oxyhemoglobin
concentration decreased and in one increased as a consequence of the 2-Hz rTMS. To locate the origin of the measured
NIRS responses, methods have to be developed to investigate TMS-induced scalp muscle contractions. In the future,
multimodal measurements may prove useful in monitoring or treating diseases such as stroke or Alzheimer's disease.
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