Near‐infrared study of fluctuations in cerebral hemodynamics during rest and motor stimulation: Temporal analysis and spatial mapping

Abstract

We have noninvasively studied the motor cortex hemodynamics in human subjects under rest and motor stimulation conditions using a multichannel near‐infrared tissue spectrometer. Our instrument measures optical maps of the cerebral cortex at two wavelengths (758 and 830 nm), with an acquisition time of 160 ms per map. We obtained optical maps of oxy‐ and deoxy‐hemoglobin concentration changes in terms of amplitudes of folding average, power spectrum and coherence at the stimulation repetition frequency, and the phase synchronization index. Under periodic motor stimulation conditions, we observed coherence and frequency or phase synchronization of the local hemodynamic changes with stimulation. Our main findings are the following: (1) The amplitude of the hemodynamic response to the motor stimulation is comparable to the amplitude of the fluctuations at rest. (2) The spatial patterns of the oxy‐ and deoxy‐hemoglobin responses to the stimulation are different. (3) The hemodynamic response to stimulation shows a spatial localization and a level of phase synchronization with the motor stimulation that depends on the stimulation period.

Spectral Analysis of Event-Related Hemodynamic Responses in Functional Near Infrared Spectroscopy

“…Our analysis has covered up to 330 mHz range since this was the cut-off frequency of the built-in RC-filter in the fNIRS device. These bands are found to be very similar to those in related studies (Hu et al, 1999;Kuo et al, 1998;Obrig et al, 2000a;Franceschini et al, 2000;Toronov et al, 2000).…”

“…the "centered" Gamma function, has its peak located within the 30-50 mHz range (see Fig. 4), the narrow B-band should be related to taskrelated cognitive activity of the subject (Cordes et al, 2001;Toronov et al, 2000). The larger C-band is also assumed to carry cognitive activity related information, most probably due to the periodicity of the target stimuli sequence as we will explore more in detail in the next section.…”

“…Efforts for characterizing the components in the spectra have concentrated on establishing a physiological correspondence with the peaks or the energy bands. Functional MRI and transcranial Doppler sonography studies have proposed several association mechanisms of vasomotor dynamics while emphasizing the fact that a strong signal, the brain hemodynamic response, exists and dominates the lower portion of the spectrum computed from temporal neuroimaging data (Obrig et al, 2000a;Franceschini et al, 2000;Prince et al, 2003;Toronov et al, 2000).…”

“…breathing, heart beat etc. ), other bands are affected by psychological or pathological conditions (or vice versa) through which degradation of task performance can be monitored (Kim and Ugurbil, 2002;Franceschini et al, 2000;Obrig et al, 2000a;Toronov et al, 2000).…”

The roles of changes in deoxyhemoglobin concentration and regional cerebral blood volume in the fMRI BOLD signal

“…In recent years many NIRS studies have demonstrated that cerebral hemodynamic changes associated with functional brain activity can be assessed noninvasively in adult human subjects (Benaron and Stevenson, 1994;Obrig et al, 2000). Several types of brain activity have been studied, including motor activity Colier et al, 1999;Toronov et al, 2000Toronov et al, , 2001Franceschini et al, 2000), visual activation (Ruben et al, 1997;Kato et al, 1993), auditory stimulation (Sakatani et al, 1999), and the performance of different cognitive tasks (Chance et al, 1993;Villringer et al, 1993). Kleinschmidt et al (1996) were first to measure simultaneously the BOLD fMRI signal and hemoglobin changes using NIRS.…”