Inability to directly detect magnetic field changes associated with neuronal activity

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.