Journal
MAGNETIC RESONANCE IN MEDICINE
Volume 72, Issue 5, Pages 1311-1319Publisher
WILEY-BLACKWELL
DOI: 10.1002/mrm.25051
Keywords
functional MRI; retina; optic lobe; electroretinogram; local field potential; cephalopod
Funding
- NIH [RO1EB015023, R21EB004753]
- NSF [IOS-1021909]
- China national strategic basic research 973 program [2012CB720701]
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PurposeDespite the efforts that have been devoted to detecting the transient magnetic fields generated by neuronal firing, the conclusion that a functionally relevant signal can be measured with MRI is still controversial. For human studies of neuronal current MRI (nc-MRI), the blood-oxygen-level-dependent (BOLD) effect remains an irresolvable confound. For tissue studies where hemoglobin is removed, natural sensory stimulation is not possible. This study investigates the feasibility of detecting a physiologically induced nc-MRI signal in vivo in a BOLD-free environment. MethodsThe cephalopod mollusc Octopus bimaculoides has vertebrate-like eyes, large optic lobes (OLs), and blood that does not contain hemoglobin. Visually evoked potentials were measured in the octopus retina and OL by electroretinogram and local field potential. nc-MRI scans were conducted at 9.4 Tesla to capture these activities. ResultsElectrophysiological recording detected strong responses in the retina and OL in vivo; however, nc-MRI failed to demonstrate any statistically significant signal change with a detection threshold of 0.2 degrees for phase and 0.2% for magnitude. Experiments in a dissected eye-OL preparation yielded similar results. ConclusionThese findings in a large hemoglobin-free nervous system suggest that sensory evoked neuronal magnetic fields are too weak for direct detection with current MRI technology. Magn Reson Med 72:1311-1319, 2014. (c) 2013 Wiley Periodicals, Inc.
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