Octopus visual system: a functional MRI model for detecting neuronal electric currents without a...

Area of Science:

• Neuroscience
• Biophysics
• Medical Imaging

Background:

• Detecting magnetic fields from neuronal firing with MRI remains challenging.
• The blood-oxygen-level-dependent (BOLD) effect confounds human neuronal current MRI (nc-MRI) studies.
• Previous methods for tissue studies required hemoglobin removal, precluding natural stimulation.

Purpose of the Study:

• To investigate the feasibility of detecting physiologically induced nc-MRI signals in vivo.
• To explore a BOLD-free environment for nc-MRI signal detection.
• To assess the detectability of neuronal magnetic fields in a hemoglobin-free organism.

Main Methods:

• Utilized Octopus bimaculoides, possessing vertebrate-like eyes, large optic lobes (OLs), and hemoglobin-free blood.
• Measured visually evoked potentials in the retina and OL via electroretinogram and local field potential.
• Conducted nc-MRI scans at 9.4 Tesla to correlate with electrophysiological recordings.

Main Results:

• Strong electrophysiological responses were detected in the octopus retina and OL in vivo.
• nc-MRI failed to show statistically significant signal changes.
• Detection thresholds for phase (0.2°) and magnitude (0.2%) were not met.

Conclusions:

• Sensory-evoked neuronal magnetic fields in a large, hemoglobin-free nervous system are too weak for current MRI detection.
• Direct detection of neuronal magnetic fields using MRI technology faces significant limitations.
• Further advancements in MRI sensitivity are needed for direct neuronal magnetic field imaging.