Simultaneous DC-magnetoencephalography and near-infrared spectroscopy: can we detect pathophysiologically relevant parameters non-invasively in patients with stroke?

Introduction: Important pathophysiological stroke concepts include anoxic depolarization, periinfarct depolarization and spreading depression. These pathophysiological processes are accompanied by DC-currents as well as oxy- and deoxy-hemoglobin concentration changes, as shown in invasive animal studies. For the non-invasive recording of these phenomena in humans and the analysis of the interaction between cortical neuronal activity and vascular/metabolic supply during these pathophysiological cascades the combination of DC-magnetoencephalography (DC-MEG) and time resolved near-infrared spectroscopy (tr-NIRS) is an neurophysiological promising tool applicable in patients.

Objective: During a physiological motor test condition we used simultaneously DC-MEG and tr-NIRS in order to learn whether cortical DC-field changes as well as oxy- and deoy-hemoglobin changes can be monitored non-invasively in healthy subjects and in ischemic stroke patients.

Methods: Four healthy subjects and three patients with subacute ischemic stroke performed self-paced periods of simple finger movements using the right hand (30s movements/30s rest; n=30). DC-MEG and tr-NIRS signals were recorded simultaneously over the left primary motor cortex. By measuring the time of flight of photons, tr-NIRS allowed to separate between deep and superficial absorption changes.

Results: In 3/4 healthy subjects and 2/3 ischemic stroke patients time courses of DC-MEG and tr-NIRS signals followed closely the motor task cycles revealing statistically significant differences between finger movement and rest periods. In most cases the analysis of variance of photon time of flight demonstrated hemodynamic/metabolic changes originating from a deeper layer, i.e. the cortex. In artifact free signals the temporal correlation of both signals was analyzed in more detail.

Conclusions: This study demonstrates the feasibility to non-invasively long-time monitor and analyze cortical low amplitude DC-fields, deoxy- and oxy-Hb simultaneously in healthy subjects and in patients with ischemic stroke. This combined methodology might be a helpful tool to scrutinise pathophysiological stroke concepts in humans.