Direct Imaging of Neuronal Activity using fMRI

"Direct Imaging of Neuronal Activity" using fMRI (Functional Magnetic Resonance Imaging)

Reference: Toi PT, Jang HJ, Min K, et al. In vivo direct imaging of neuronal activity at high temporospatial resolution. Science. 2022;378(6616):160-168. doi:https://doi.org/10.1126/science.abh4340 (Preprint) 


fMRI pioneer and director of the NIH fMRI facility, Peter Bandettini: "It is a paper that did cause a huge stir. I had a bunch of neuroscientists give me a call or just email me saying "what's up with this paper, should I be doing this?". Also, we have been trying to do this in our group". (OHBM Neurosalience podcast - https://www.youtube.com/watch?v=vGhf9utIXwM&t=1208s)

The article had an editorial expression of concern four months ago. The following news article explains that there had been two efforts that failed to replicate the results: https://www.the-scientist.com/news/is-diana-fmri-data-real-71285

The issues may be related to selecting specific experiments/trials for inclusion into the dataset. 

One of the authors of the study mentions: "it was better to average over earlier trials when the neuronal response is “fresh” and to take breaks between trials. He also encouraged averaging across animals to minimize baseline fluctuations that he believes come from spontaneous neuroactivity." He adds that he has replicated the technique in both mice and humans and that he expects to publish that work soon.


"Can MRI Be Used as a Sensor to Record Neural Activity?"

Reference: Roth BJ. Can MRI Be Used as a Sensor to Record Neural Activity? Sensors. 2023;23(3):1337-1337. doi: https://doi.org/10.3390/s23031337

Spins are like small magnets or compasses and can be compared to clocks whose hands move in 360 degrees.

The electric activity of the brain creates a changing magnetic field. 

That magnetic field will push the spins: it will be as if pushing the hands of clocks and changing their phase in the 360 degree circle.

If we can measure the phase shift, we can calculate the magnetic field. Is the phase shift measurable?

Related excerpts, mainly to illustrate the applicable reasoning:

"If the cardiac magnetic field in the heart produces a 10 nT field lasting 0.5 ms, the phase shift will be about 0.001 radians, or roughly a tenth of a degree."

Manbir Singh "concluded that measurement of action currents would require detecting a phase shift of about a third of a degree". 

"Bodurka and Bandettini performed similar experiments and concluded that a magnetic field as small as 0.2 nT lasting for 40 ms could be detected using MRI".

This article also cites the advantages of using low magnetic fields as opposed to high magnetic fields.