Using near-infrared-spectroscopy a slow signal due to hemodynamic changes following brain activity is well characterized, while a fast signal is not enough investigated. With our frequency-domain-spectrometer and two different sensors we detected both signals.

We obtained maps of cerebral hemoglobin concentration changes by near-infrared spectroscopy during functional stimulation and physiological activity at rest. The correlation and phase shift between locations were characterized by phase portraits and the phase synchronization index.

In order to study the behavior of cerebral physiological parameters and to further the understanding of the fMRI blood-oxygen-level-dependent (BOLD) effect, we have recorded simultaneously multi-source frequency-domain near-infrared and BOLD fMRI signals during motor functional activation in humans. From the near-infrared data we obtained information on the changes in cerebral blood volume and oxygenation. In order to relate our observations to changes in cerebral blood flow we employed the "balloon" model of cerebral perfusion. Our data showed that the deoxyhemoglobin concentration is the major factor determining the time course of the BOLD signal.

We applied Near-Infrared Spectroscopy for the investigation of cerebral oxygenation during obstructive sleep apnea. We found a relatively large decrease in brain oxygenation during apnea and the peak of deoxygenation occurs after resumption of breathing.

We measure cerebral hemodynamic fluctuations simultaneously by near-infrared spectroscopy and magnetic resonance imaging during functional stimulations. Our repetitive stimulation protocol includes a variety of epochs differing in duration of stimulation and relaxation periods, which allows generating hemodynamic signals highly synchronous with stimulation sequence. Our goals are to compare results of temporal analysis of hemodynamic fluctuations measured by near-infrared spectroscopy and high-speed magnetic resonance imaging, and to compare optical maps of brain activity based on the results of temporal analysis of NIRS signals with magnetic resonance images.