# Direct Evidence for the Feedforward Neurovascular Coupling Mechanism in Humans During Task Onset: An EEG-fNIRS-TCD Multimodal Imaging Study

## TL;DR

This study shows that brain activity and blood flow in small vessels predict larger artery blood flow during tasks, supporting a one-way brain-blood flow mechanism in humans.

## Contribution

First successful concurrent assessment of neuronal, microvascular, and arterial responses to quantify neurovascular coupling in humans.

## Key findings

- Neuronal activity and microvascular oxygenation predicted upstream arterial blood flow during task onset.
- The neurovascular coupling response was consistent across participants, with minimal influence from concussion history or mental health.
- Sex, age, and cardiorespiratory fitness influenced baseline and peak hemodynamic values.

## Abstract

What are the main findings?
Concurrent EEG, fNIRS, and TCD measurements showed that neuronal activity and microvascular oxygenation predicted upstream arterial blood flow during task onset, supporting a unidirectional feedforward neurovascular coupling response.The overall NVC response was consistent across participants, with minimal influence of concussion history, mental health, or learning disabilities, although sex, age, and cardiorespiratory fitness influenced baseline and peak hemodynamic values.

Concurrent EEG, fNIRS, and TCD measurements showed that neuronal activity and microvascular oxygenation predicted upstream arterial blood flow during task onset, supporting a unidirectional feedforward neurovascular coupling response.

The overall NVC response was consistent across participants, with minimal influence of concussion history, mental health, or learning disabilities, although sex, age, and cardiorespiratory fitness influenced baseline and peak hemodynamic values.

What is the implication of the main findings?
This study represents the first successful concurrent assessment of neuronal, microvascular, and intracranial arterial responses to quantify neurovascular coupling in humans; providing support for the feedforward neurovascular coupling model in which neuronal activation and microvascular changes drive upstream cerebrovascular responses during cognitive and motor tasks.The findings demonstrate the utility of multimodal imaging (EEG–fNIRS–TCD) for characterizing integrated neurovascular responses in humans, providing a framework for future studies of cerebrovascular and neurological health.

This study represents the first successful concurrent assessment of neuronal, microvascular, and intracranial arterial responses to quantify neurovascular coupling in humans; providing support for the feedforward neurovascular coupling model in which neuronal activation and microvascular changes drive upstream cerebrovascular responses during cognitive and motor tasks.

The findings demonstrate the utility of multimodal imaging (EEG–fNIRS–TCD) for characterizing integrated neurovascular responses in humans, providing a framework for future studies of cerebrovascular and neurological health.

This investigation assessed the neurovascular coupling response through integrated assessments of neuronal function [electroencephalography (EEG)], microvascular oxygenation concentrations [functional near-infrared spectroscopy (fNIRS)], and arterial responses [transcranial Doppler ultrasound (TCD)]. The NVC response was assessed in 113 participants (86 females, aged 19–40 years) during visual (“Where’s Waldo?”) and motor (finger tapping) tasks. Block-averaged, time–frequency power was computed from the EEG data, while hemodynamic response functions were obtained from the fNIRS and TCD metrics. Granger causality assessed the predictiveness between EEG-fNIRS-TCD waveforms for each participant and was converted into a percentage of individuals displaying a significant value. Linear models were computed to determine the influence of sex, concussion history, young adulthood age, cardiorespiratory fitness, and mental health/learning disabilities on NVC parameters. During the initial 10 s of task onset, unidirectional predictiveness was weak to very strong for EEG-TCD (range: 47–83%) and fNIRS-TCD (44–92%) relationships; however, very weak to weak predictiveness was seen for the E0EG-fNIRS (0–29%) relationship for both tasks. Aside from known sex-, age-, and fitness-based influences on baseline/peak hemodynamic values (p < 0.050), the addition of concussion history and mental health/learning disabilities had minimal influence on NVC responses (p > 0.050). The findings demonstrated a unidirectional feedforward mechanism from the neuronal and microvasculature to the upstream arteries during task onset.