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

Introduction: Important pathophysiological stroke concepts include anoxic depolarisation, periinfarct-depolarisation and spreading depression. In this regard highly relevant parameters are DC-currents as well as oxy- and deoxy-hemoglobin. For recordings of slow neuronal activity (<0.1Hz) DC-magnetoencephalography provides advantages in comparison to DC-electroencephalography (DC-EEG) which is susceptible for drift artifacts generated mainly at the electrode-skin interface. In animal models magnetic field changes resulting from spreading depression and concomitant changes of oxy- and deoxy-hemoglobin have been recorded invasively.

Objective: Here, in a physiological test condition, i.e. during a prolonged simple motor task, we proved, that using simultaneously DC-MEG and time resolved near infrared spectroscopy (trNIRS) cortical DC-fields as well as oxy- and deoxy-hemoglobin changes can be recorded non-invasively in healthy subjects and in patients suffering from stroke.

Methods and results: We recorded DC-MEG and trNIRS simultaneously over the left primary motor cortex hand area in healthy subjects and stroke patients during prolonged finger movement periods of the right hand (30s. movement/30s. rest; n=30). DC-fields and trNIRS parameters followed closely the motor task cycles revealing statistically significant differences between periods of finger movements and rest. In subjects with sufficient signal-to-noise ratio the analysis of variance of photon time of flight demonstrated hemodynamic changes originating from a deeper layer, i.e., the cortex. Notably, while onset and relaxation started simultaneously trNIRS signals reached 50% of the maximum level 1–4s later than MEG-signals.

Discussion and conclusion: The feasibility to non-invasively monitor cortical low amplitude DC-fields, deoxy- and oxy-Hb simultaneously in healthy humans and also in stroke patients might allow to scrutinise pathophysiological stroke concepts, e.g. anoxic depolarisation, periinfarct-depolarisation and spreading depression. Notably fields of even higher magnitude (up to 2 pT) than resolved in this MEG-study have been shown in animal spreading depression studies.

This study was supported by DFG grant Cu 36/1–3,5,6 and BMBF grants GF GO 01184601 and 01 GO 0208.