An international research team from Berlin, Ljubljana, and Warsaw has quantified how long it takes for blood vessels to respond to neural activity during simple motor tasks, and how stable this delay is across individuals and repeated trials.
The findings have implications for the interpretation of functional brain imaging techniques, particularly those that rely on vascular signals rather than direct measures of neuronal activity.
Brain function can be studied in two main ways: by measuring the electrical activity of neurons, or by tracking changes in blood flow and oxygen delivery that supply those neurons with energy.
Neurons have no internal energy reserves and depend on a continuous supply of oxygen and glucose from the bloodstream. This supply is regulated through neurovascular coupling, a process in which neural activity triggers local changes in blood flow. Functional magnetic resonance imaging (fMRI), widely used in neuroscience and clinical research, relies on this mechanism by detecting changes in blood oxygenation rather than neuronal signals themselves.
In a study published in NeuroImage, the researchers examined whether neural and vascular signals could be measured simultaneously and used to estimate the delay between them during motor activity.
They combined magnetoencephalography (MEG) and functional near-infrared spectroscopy (fNIRS). MEG, using a rigid, individually fitted 3D-printed helmet, recorded weak magnetic fields produced by synchronized neuronal activity. fNIRS measured changes in oxygenated and deoxygenated hemoglobin in blood supplying the cerebral cortex.
Participants performed two right-hand motor tasks: squeezing a ball and executing a sequence of finger taps in which each finger touched the thumb in turn. MEG recordings showed the expected movement-related pattern, with reduced power in specific brain rhythms during movement and a rebound afterward. At the same time, fNIRS detected a typical vascular response in sensorimotor regions, marked by increased oxygenated hemoglobin and decreased deoxygenated hemoglobin.
The strongest correlation between neuronal and vascular signals occurred with a delay of approximately four to seven seconds. The study also found that more precise finger movements produced a less consistent vascular response across individuals, but a stronger coupling between MEG and fNIRS signals, particularly in the alpha frequency band.
According to the researchers, quantifying the timing and variability of neurovascular coupling can improve the interpretation of standard imaging methods and help distinguish normal vascular responses from pathological ones.
The combined MEG–fNIRS approach may also enable more patient-friendly brain measurements. Unlike MRI scanners, the setup allows sensors to be placed close to the head and tolerates small movements, making it suitable for studies involving children, stroke patients, and individuals with motor impairments.
In the longer term, simultaneous measurement of neural and vascular activity could complement existing brain imaging by showing not only where activity occurs, but also whether blood vessels respond appropriately—an important factor in many neurological conditions. (PAP)
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