Functional MRI now maps the human spinal cord, in 22 volunteers

Nawal Kinany spent eight years on a blur. Her subject was not the moon but the human spinal cord, and the faint, noisy signal that functional magnetic resonance imaging, or fMRI, picks up from it. The picture she helped sharpen now guides treatments for paralysis, and it may soon do the same for stroke and Parkinson's.

fMRI does not see neurons fire. It tracks the rush of oxygen-rich blood that follows their activity, a few seconds late, with one snapshot every two or three seconds. In the brain, that is enough to show where activity happens and how it shifts. In the spinal cord, a structure barely a centimeter across, every heartbeat and every breath adds noise that can drown the signal entirely. Dimitri Van De Ville, who heads EPFL's Medical Image Processing Laboratory, has built his career on the mathematics that pull activity out of that noise.

The project began in 2016, when Kinany was splitting her doctoral work between two EPFL labs at Campus Biotech in Geneva. Her team recorded brain activity, muscles and movements in people paralyzed after a stroke, and something seemed to be missing between them. 'We realized that there was kind of the missing link between all of this, which was the spinal cord,' she says. Colleagues were not convinced. 'The spinal cord is a tube,' they told her.

The new result comes from a preprint, posted before peer review, in which doctoral student Ekansh Sareen worked with Friedhelm Hummel's team. They used transcranial magnetic stimulation, or TMS, a coil held against the scalp that sends a brief magnetic pulse into the motor cortex, while imaging the spinal cords of 22 volunteers. Weak pulses lit up only the cord's sensory side. Stronger ones spread through an intermediate zone to the motor neurons that make the hand twitch. Sareen compares the cord to an information railway, where some switches change how the traffic flows. According to the team, it is the first time anyone has watched, in humans, what a pulse to the brain does in the cord.

None of this is a therapy yet. Every spinal cord is wired a little differently, so the nerves serving a given muscle can join the cord a segment higher or lower from one person to the next. That matters for implants: in 2022, the Lausanne center .NeuroRestore reported that three people with complete paralysis could stand and walk again with a stimulator placed on the spinal cord. The team is now bringing the imaging method to CHUV, Lausanne's university hospital, ahead of a trial in stroke. No start date for that trial is given.

For stroke patients, the gain would be a way to tailor rehabilitation and implants to each person's own cord rather than to an average one. For people with paralysis, it would be a finer map of which spinal circuits can be stimulated. The timeline stays open: the study is a preprint on 22 people, and the stroke trial has no announced date.