Non-invasive assessment of neurovascular coupling in the time range of milliseconds

Background and Purpose: The objective of the present study was to investigate cortical neuronal and vascular changes as well as their interaction in physiological and pathological conditions. Using simultaneously non-invasive DC-magnetoencephalography (dcMEG) and multichannel, time-resolved near-infrared spectroscopy (trNIRS) the changes in neuronal and vascular signals as well as their coupling processes were characterized. We used a unique DC-MEG recording technique which became feasible inside the new Berlin magnetically shielded room (BMSR 2). This technique allows to characterize fast dynamics of neurovascular coupling from DC up to the kHz frequency range. This is of great importance, e.g., for the description of transition phenomena at beginning and end of long lasting activations.

Methods: A simple motor condition was used to induce physiological cortical activity changes. In part I of the study, 20 healthy subjects performed self-paced simple finger movements (30-second periods of finger movements, always separated by 30-second periods of rest, for a total of 30 minutes). DcMEG signals and trNIRS signals were recorded over the contralateral primary motor cortex. In part II of the study, 15 patients with acute ischemic stroke and contralateral arm paresis were investigated over the affected and unaffected hemispheres, resp. Thereby, longitudinal measurements on day 1, week 4 and week 12 were performed.

Results: In healthy subjects (part I), the time courses of the neuronal (dcMEG) and vascular signals (trNIRS) followed closely the motor task cycles revealing significant differences between finger movement and rest periods. The synchronous triple measurement of dcMEG, trNIRS and electromyographic activity enabled a coupling analysis on the level of unaveraged time series. The difference in transition time for neuronal and vascular responses due to sustained finger movements was reflected in an asymmetric dcMEG and trNIRS response. The vascular response did not follow the neuronal rapid variations due to individual finger movements and was delayed by four to five seconds. The data of the longitudinal patient's measurements (part II) are in progress.

Conclusions: This study demonstrates that a combined non-invasive analysis of neuronal and vascular signals is feasible in healthy subjects and even in patients with acute ischemic stroke. This technique facilitates conclusions about the temporal aspects of neurovascular coupling in physiological as well as pathophysiological conditions.