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Detecting Pre-Stimulus Source-Level Effects on Object Perception with Magnetoencephalography
Published on: July 26, 2019
Inability to directly detect magnetic field changes associated with neuronal activity
Laura M Parkes1, Floris P de Lange, Pascal Fries
1F.C. Donders Center for Cognitive Neuroimaging, Radboud University, Nijmegen, The Netherlands. laupar@liverpool.ac.uk
Abstract:
The ability to directly detect neuronal magnetic fields by MRI would help investigators achieve the "holy grail" of neuroimaging, namely both high spatial and temporal resolution. Both positive and negative findings have been reported in the literature, with no clear consensus as to the feasibility of direct detection. The aim of this study was to replicate one of the most promising published in vivo results. A second aim was to investigate the use of steady-state visual evoked potentials (ssVEPs), which give a large evoked response and offer a well-controlled approach because the frequency of the neuronal response can be dictated by the experimenter. For both studies we used a general linear model (GLM) that included regressors for both the expected blood oxygen level-dependent (BOLD) signal and the magnetic source (MS) signal. The results showed no activity that could be attributed to the neuromagnetic signals in either study, and no frequency component corresponding to the frequency of the ssVEPs. This study demonstrates that for the particular stimuli and hardware used, the sensitivity of the magnitude MRI signal to detect evoked neuronal currents is too low to be of practical use.
Insights
Directly detecting neuronal magnetic fields with MRI remains challenging. This study found MRI signal sensitivity too low for practical detection of evoked neuronal currents using specific stimuli and hardware.
Area of Science:
- Neuroimaging
- Biophysics
- Magnetic Resonance Imaging
Background:
- Direct detection of neuronal magnetic fields via MRI offers potential for high spatial and temporal resolution neuroimaging.
- Previous studies report conflicting findings regarding the feasibility of this technique, lacking a clear consensus.
- Steady-state visual evoked potentials (ssVEPs) provide a controlled method to study neuronal responses due to their large, experimenter-dictated frequency.
Purpose of the Study:
- To replicate promising in vivo results for direct neuronal magnetic field detection using MRI.
- To investigate the utility of ssVEPs in conjunction with MRI for detecting neuronal activity.
- To assess the sensitivity of MRI magnitude signals to evoked neuronal currents.
Main Methods:
- Utilized a general linear model (GLM) incorporating regressors for both blood oxygen-level-dependent (BOLD) and magnetic source (MS) signals.
- Employed steady-state visual evoked potentials (ssVEPs) as a controlled neuronal response stimulus.
- Conducted experiments with specific stimuli and hardware configurations to test MRI sensitivity.
Main Results:
- No significant activity attributable to neuromagnetic signals was detected in either study.
- No specific frequency component corresponding to the ssVEP frequency was identified.
- The sensitivity of the MRI magnitude signal was insufficient for practical detection of evoked neuronal currents.
Conclusions:
- Under the tested conditions (specific stimuli and hardware), the MRI signal magnitude lacks the sensitivity to detect evoked neuronal currents.
- Direct detection of neuronal magnetic fields using current MRI technology and methods faces significant sensitivity limitations.
- Further advancements in MRI hardware or signal processing may be necessary to achieve direct neuronal magnetic field detection.
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