Measurement technology to investigate neurovascular coupling

Every two minutes in Germany, one person suffers a stroke. About one third of the affected do not survive the sudden lack of blood in the brain, many others are left with serious disabilities.

Since the brain is a high-performance organ with an immense energy requirement - if the supply of oxygen is interrupted, it reacts with paralyses, impaired speech and vision.

To improve the understanding of the underlying processes in the brain, researchers from the Physikalisch-Technische Bundesanstalt (PTB) are working on experiments in neurovascular coupling: They are researching the temporal correlation between the oxygen requirement of the nerve cells and the oxygen supply through the blood. They have succeeded here for the first time in vivo with a temporal resolution of 100 ms.

To achieve this the neuronal activity (brain current) was measured simultaneously with the accompanying vascular signal changes (blood volume and oxygenation) during sequences of finger movement. This combined study is only possible within the magnetically shielded room at PTB (BMSR-2) as this room offers a unique environment for DC-magnetoencephalography, which is a measure of neuronal activity. The concentration changes of oxygenated and deoxygenated hemoglobin are assessed optically using another advanced technique, time resolved near infrared spectroscopy, which is compatible with DC- magnetoencephalography.

The results show clearly, that the instantaneous change in neuronal activity is followed by a slower change on the scale of seconds in the blood supply. This temporal relation might be altered in stroke patients with possible new diagnostical insights. The quantitative characterization of neuro-vascular coupling has another important application: Functional magnetic resonance imaging (fMRI) relies on vascular changes, whereas electro- and magnetoencephalography (EEG, MEG) are direct measures of neuronal activity. The experiments introduced here are designed to be able to relate one type of measurement to the other.