Abstract
Previous functional magnetic resonance imaging (fMRI) studies have shown that a subgroup of patients diagnosed as being in a vegetative state are aware and able to communicate by performing a motor imagery task in response to commands. Due to the fMRI's cost and accessibility, there is a need for exploring different imaging modalities that can be used at the bedside. A promising technique is functional near infrared spectroscopy (fNIRS) that has been successfully applied to measure brain oxygenation in humans. Due to the limited depth sensitivity of continuous-wave NIRS, time-resolved (TR) detection has been proposed as a way of enhancing the sensitivity to the brain, since late arriving photons have a higher probability of reaching the brain. The goal of this study was to assess the feasibility and sensitivity of TR fNIRS in detecting brain activity during motor imagery. Fifteen healthy subjects were recruited in this study, and the fNIRS results were validated using fMRI. The change in the statistical moments of the distribution of times of flight (number of photons, mean time of flight and variance) were calculated for each channel to determine the presence of brain activity. The results indicate up to an 86% agreement between fMRI and TR-fNIRS and the sensitivity ranging from 64 to 93% with the highest value determined for the mean time of flight. These promising results highlight the potential of TR-fNIRS as a portable brain computer interface for patients with disorder of consciousness.
Highlights
Consciousness can be empirically defined as the state of being awake and aware of oneself and one’s surroundings [1]
A significant decrease in N, and V was found during motor imagery (MI) periods, reflecting the increased oxyhemoglobin concentration caused by functional hyperemia
The aim of this study was to assess the ability of functional near infrared spectroscopy (fNIRS) to detect MI activation consistently across a group of healthy participants in order to assess its validity for translation to disorders of consciousness (DOC) patients
Summary
Consciousness can be empirically defined as the state of being awake and aware of oneself and one’s surroundings [1]. The presence of awareness is measured by the ability to follow commands, either behaviourally or verbally [2] Because of this reliance on observable responses, a subset of patients who retain some cognitive function but are unable to follow commands are frequently diagnosed incorrectly as suffering from unresponsive wakefulness syndrome (UWS) or what is commonly referred to as a vegetative state [1,3]. Using a motor imagery (MI) task (i.e. imagine playing tennis) and by activating the brain regions associated with motion planning (i.e. supplementary motor area (SMA) and premotor cortex (PMC)), the patient was able to follow commands and produce brain activity that was indistinguishable from that of healthy volunteers [4] This finding has revolutionized studies involving patients with disorders of consciousness (DOC), with various follow up studies demonstrating the ability to communicate with VS/UWS patients using fMRI [5]
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