As explained in my new book on nerve and spinal cord regeneration (see section 2.4.8), epidural electrical stimulation (EES) can be used to treat the chronic pain syndromes associated with a transverse section of the spinal cord. In some experimental approaches, improvements in somatomotor function and urinary bladder control have also been observed. Patients particularly benefit from electrical stimulation treatment when rehabilitative measures are implemented at the same time.
In a study published in Nature Medicine in 2022 from the laboratory of Grégoire Courtine, who heads the NeuroRestore laboratory at the École Polytechnique Fédérale de Lausanne (EPFL) together with Jocelyne Bloch, it has now been shown for the first time that defined step sequences and walking can also be restored via direct stimulation of the nerves connected to the lumbar spinal cord. Here, sensitive (afferent) posterior root fibers were electrically stimulated by an EES in the area of their entry into the spinal cord and subsequently activated the motor neurons in the anterior horn of the associated spinal cord segment. Targeted stimulation of individual dorsal roots thus allowed modulation of specific ensembles of motor neurons. Thus, in contrast to continuous EES, their natural spatiotemporal activation pattern during walking is reproduced.
To this end, the authors developed an area-based, so-called paddle electrode, which can stimulate previously identified root nerves of different segments via a special arrangement of several small electrodes. In conjunction with a computerized system combining high-resolution structural and functional imaging, the surgical placement of the electrode was optimized and a complex stimulation program was configured via custom-developed software.
This biomimetic EES method enabled standing and walking as well as cycling, swimming and trunk control within one day in three individuals with chronic and complete paraplegia. Responsible for this dramatically increased efficacy compared to previous studies was the specific electrode placement that targeted the sacral, lumbar, and lower thoracic posterior roots.
Although the three participants in the study were able to move independently, they did not regain their natural movements. However, two subjects were able to modulate their leg motor control even during EES, suggesting that the stimulation enhanced residual signals from remaining descending pathways. In the course of neurorehabilitation, voluntary muscle activation was detectable even without EES, so that indeed plasticity of still intact spinal cord pathways seems to be responsible for this recovery.
The authors of the study had previously shown that neurorehabilitation using EES allows neurological recovery after incomplete traumatic brain injury. Therefore, it is likely that future development of neurotechnology tailored to the patient may stimulate the dorsal root nerves of the spinal cord at all levels of the neuraxis to positively affect arm or hand motor function, as well as bladder/bowel function and hemodynamics, if needed, in addition to trunk and leg movements.
Reference:
Rowald A, Komi S, Demesmaeker R, ..., Bloch J, Courtine G (2022) Activity-dependent spinal cord neuromodulation rapidly restores trunk and leg motor functions after complete paralysis. Nature Medicine 28:260
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