Cerebral Hemodynamics Measured by Near-Infrared Spectroscopy at Rest and During Motor Activation

Abstract

Near-infrared spectroscopy and imaging are powerful tools to detect and continuously monitor the cerebral hemodynamic and oxygenation changes induced by brain activity. However, in addition to the focal neuronal-activation-induced hemodynamic signals, near-infrared methods are also sensitive to the cerebral hemodynamic fluctuations of systemic origin associated, for instance, with the arterial pulse, respiration, and heart rate fluctuations. We have used near-infrared spectroscopy to non-invasively measure the cerebral hemodynamics in a human subject at rest. We have observed hemoglobin oscillations at the heart rate (~1 Hz), respiratory rate (~0.2 Hz), and at lower frequencies that are associated with heart rate fluctuations and vasomotion activity. With near-infrared imaging, we have measured the spatial maps of temporal changes in the cerebral oxy- and deoxy- hemoglobin concentrations during motor activity (hand tapping). We have found a more localized activation-induced response in the deoxy-hemoglobin map with respect to the oxy-hemoglobin map. This result can be explained by the observed synchronization between the sequence of tapping/rest periods and several systemic physiological oscillation such as the arterial pulse, respiration, and heart rate fluctuations.