Using fMRI to investigate the potential cause of inverse oxygenation reported in fNIRS studies of motor imagery

Abstract

Motor imagery (MI) is a commonly used cognitive task in brain-computer interface (BCI) applications because it produces reliable activity in motor-planning regions. However, a number of functional near-infrared spectroscopy (fNIRS) studies have reported the unexpected finding of inverse oxygenation: increased deoxyhemoglobin and decreased oxyhemoglobin during task periods. This finding questions the reliability of fNIRS for BCI applications given that MI activation should result in a focal increase in blood oxygenation. In an attempt to elucidate this phenomenon, fMRI and fNIRS data were acquired on 15 healthy participants performing a MI task. The fMRI data provided global coverage of brain activity, thus allowing visualization of all potential brain regions activated and deactivated during task periods. Indeed, fMRI results from seven subjects included activation in the primary motor cortex and/or the pre-supplementary motor area during the rest periods in addition to the expected activation in the supplementary motor and premotor areas. Of these seven subjects, two showed inverse oxygenation with fNIRS. The proximity of the regions showing inverse oxygenation to the motor planning regions suggests that inverse activation detected by fNIRS may likely be a consequence of partial volume errors due to the sensitivity of the optodes to both primary motor and motor planning regions.

Assessing Time-Resolved fNIRS for Brain-Computer Interface Applications of Mental Communication

“…To improve the sensitivity of fNIRS to MI, time-resolved (TR) fNIRS has been investigated (Abdalmalak et al, 2017a(Abdalmalak et al, , 2020. TR detection involves recording the arrival times of single photons, which can be used to enhance depth sensitivity since photons that interrogate superficial tissue are detected earlier than photons that travel farther (i.e., deeper).…”

Incorporating early and late-arriving photons to improve the reconstruction of cerebral hemodynamic responses acquired by time-resolved near-infrared spectroscopy

“…All data were collected using an in-house built trNIRS system. 25 – 27 The device included two pulsed laser heads emitting at and 830 nm, controlled by a Sepia II laser driver operating at 80 MHz (PicoQuant, Germany). The laser heads were coupled to multimode bifurcated fiber [ , numerical aperture , Thorlabs] to deliver the light to the scalp.…”

The Potential Role of fNIRS in Evaluating Levels of Consciousness

“…Inverse oxygenation has been attributed to a possible reduction in oxygen consumption, leading to focal deactivation (Holper et al, 2011 ). Alternatively, partial volume errors (i.e., activation in brain areas adjacent to the regions of interest) could be another potential cause (Abdalmalak et al, 2020b ). More specifically, inadvertent movement during rest periods will lead to increased activity in the primary motor cortex adjacent to the secondary motor areas.…”

“…Additionally, these patients may suffer from structural brain changes, which can affect the locations of the regions of interest. This is a major challenge considering that most fNIRS studies rely on the 10–20 international system of EEG electrode placement to guide fNIRS probe placement (Abdalmalak et al, 2020b ). In these instances, it would be important to examine the patient’s anatomical CT or MRI scans to ensure the fNIRS probes are placed over the appropriate brain areas.…”