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Natural walking with the help of a brain-spine interface after severe spinal cord injury


In my blog post of October 8, I presented a much-noticed study by Grégoire Courtine's research group from last year, which showed that electrical stimulation of individual dorsal roots in the lumbosacral spinal cord can trigger stepping movements in paraplegics. Spatially and temporally pre-programmed sequences were used to activate the motoneurons in the ventral spinal cord of a paralyzed patient that are responsible for standing and walking. However, movement sensors were required to recognize his motor intentions from residual movements to initiate the stimulation sequences. Consequently, the control of walking was not perceived as natural. In addition, it was hardly possible to adapt the leg movements to changing terrain.


In a recently published study, a wireless digital bridge was therefore developed between the brain and spinal cord, a so-called BSI (brain-spine interface), which restored natural control over the movements of the legs in order to be able to stand and walk again after paraplegia, even on irregular surfaces. Two fully implanted systems were thus integrated, enabling the recording of cortical brain activity and stimulation of the lumbosacral spinal cord wirelessly and in real time:


a, Two cortical implants with 64 electrodes are implanted epidurally over the sensorimotor cortex to record electrical activity (EEG signals). A processing unit detects the intended movement and translates this prediction into the modulation of stimulation programs targeting the dorsal root entry zones of the lumbosacral spinal cord. These stimulations are delivered by an implantable pulse generator connected to a 16-contact paddle electrode. b, Images of preoperative planning of cortical implant positions and postoperative confirmation of their location. L, left; R, right. c, Personalized computer model to predict the optimal localization of the paddle electrode to reach the dorsal root entry zones connected to the leg muscles (Fig. 1 from Lorach H, Galvez A, Spagnolo V, ..., Bloch J, Courtine G (2023) Nature 618:126).


Such a brain-spine interface thus consists of fully implanted recording and stimulation systems that establish a direct connection between cortical signals from the brain and epidural electrical stimulation at the posterior roots of the spinal cord. A BSI can be calibrated within a few minutes and remains stable for at least a year, even when used independently at home. Several patients have already been able to walk again within a day using this method. The concept of a digital bridge to the still intact spinal cord can be extended to arm and hand movements, whereby the extent of neurological recovery correlates with the severity of the lesion.


In summary, a BSI together with neurorehabilitation leads to significant neurological improvements, which currently primarily affect the control of hip muscles. As a result, a leg can be lifted against gravity without stimulation and external help, enabling paraplegics to walk again.


References:


Lorach H, Galvez A, Spagnolo V, ..., Bloch J, Courtine G (2023) Walking naturally after spinal cord injury using a brain-spine interface. Nature 618:126



Image credit: iStock/Graphic_BKK1979

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