Physiologically evoked neuronal current MRI in a bloodless turtle brain: detectable or not?

Area of Science:

• Neuroimaging
• Magnetic Resonance Imaging (MRI)
• Neurophysiology

Background:

• The feasibility of neuronal current MRI (ncMRI) remains uncertain due to conflicting reports.
• Previous human studies are limited by the inability to eliminate confounding hemodynamic effects.

Purpose of the Study:

• To assess the feasibility of detecting visually-evoked ncMRI signals.
• To investigate ncMRI in a controlled, bloodless preparation to eliminate hemodynamic influences.
• To explore ncMRI at a high magnetic field strength (9.4 T).

Main Methods:

• Utilized an ex vivo, bloodless turtle brain preparation to remove hemodynamic artifacts.
• Delivered light flashes to evoke neuronal activity and measured local field potentials (LFPs).
• Acquired interleaved MRI signals alongside LFPs at 9.4 T.

Main Results:

• Confirmed robust visually-evoked LFP signals in the turtle brain.
• No significant ncMRI signal changes were detected that synchronized with neuronal currents.
• Established detection thresholds of 0.1% for MRI magnitude and 0.1 degrees for phase signal changes.

Conclusions:

• Visually-evoked ncMRI signals in the turtle brain appear to be below the current detection limits of the applied methodology.
• The study highlights the challenges in detecting ncMRI signals, even in a preparation free of hemodynamic effects.
• Further advancements in MRI sensitivity or alternative approaches may be necessary for successful ncMRI detection.