Summary: Researchers have identified a previously unrecognized sensory pathway that connects the foot to the face on the same side of the body. This ipsilateral route appears to partially bypass the spinal cord and may help explain neurological phenomena such as referred itch and the so-called jogger’s migraine. The discovery also raises the possibility of new rehabilitation approaches for people with spinal cord injury.
Source: Curtin University
Published in Frontiers in Neuroscience: A new study describes a sensory pathway that runs down the same side of the body and can convey signals to the face from the foot even when the spinal cord is damaged. The finding may clarify some unusual clinical symptoms and points to potential therapeutic possibilities for spinal cord injury patients.
Lead author Adjunct Associate Professor Dr Morry Silberstein from the School of Molecular and Life Sciences at Curtin University underscored the central importance of the spinal cord in transmitting sensory and motor messages between the brain and the limbs. In typical physiology, sensory information travels from the limbs up through the spinal cord to reach the brain.
“An intact spinal cord is essential because it normally carries messages from the brain to the limbs and sensory information back to the brain,” Dr Silberstein said. “Previous experimental work in healthy volunteers documented ipsilateral sensory transmission, for example when immersion of one foot in painfully cold water produced increased blood flow and flushing of the face on the same side. We sought to determine whether a similar ipsilateral response could be seen in people with spinal cord injury.”
In the study, researchers tested three groups: 10 people with complete spinal cord injuries, 10 healthy volunteers tested before and after a topical capsaicin application to the lower thigh (used to temporarily block small-diameter C-fiber cutaneous conduction), and 10 healthy control participants who immersed their feet in warm water. The team measured facial perfusion (blood flow) following immersion of the foot in painfully cold water, and compared responses across conditions.
Results showed that, as in healthy volunteers, facial blood flow on the same side as the stimulated foot increased significantly in spinal cord injured patients. When capsaicin was applied to the lower thigh in healthy participants, the ipsilateral face-blushing response after cold immersion was altered: perfusion increased on the opposite side instead of the same side—suggesting interruption of the ipsilateral peripheral route. Capsaicin application did not induce the same change in two of the spinal cord injured participants who received the treatment.
Supported by skin biopsy evidence from a healthy participant, the authors propose that the pathway involves peripheral C-fiber cross-talk that can partially bypass the spinal cord. In other words, peripheral nerve fibers in the skin may communicate across segments or via local interactions so that a stimulus to the foot produces a response in the ipsilateral face without relying solely on spinal transmission.
Dr Silberstein emphasized that the findings are preliminary but encouraging. “Our initial results offer promising leads for this type of injury,” he said. “One potential application could be to train spinal cord–injured individuals to interpret facial flushing as a proxy for lower limb contact with the ground, which might aid rehabilitation strategies.”
“There is still a lot to learn about this newly discovered pathway and it is recommended that larger groups of patients with spinal cord injuries are tested to see if similar results are found.”
The research was conducted by a multidisciplinary team including collaborators from Austin Health Melbourne, Murdoch University, RMIT University, and the University of Melbourne.
Source:
Curtin University
Media Contacts:
Lucien Wilkinson – Curtin University
Image Source:
The image is in the public domain.
Original Research (open access):
“A Human Sensory Pathway Connecting the Foot to Ipsilateral Face That Partially Bypasses the Spinal Cord”. Morry Silberstein, Andrew K. Nunn, Peter D. Drummond, Dawn Wong Lit Wan, Janette Alexander, Melinda Millard and Mary P. Galea. Frontiers in Neuroscience. doi: 10.3389/fnins.2019.00519
Abstract (summary):
Human sensory transmission from limbs to the brain typically crosses and ascends through the spinal cord, but clinical descriptions and experimental findings have long suggested the existence of ipsilateral transmission and sensory effects even after spinal cord transection. To investigate this, the authors measured facial blood flow after painfully cold foot immersion in three groups: 10 complete spinal cord-injured patients, 10 healthy volunteers before and after applying a lower-thigh capsaicin block of C-fiber conduction, and 10 healthy participants who used warm immersion as a control. Ipsilateral facial perfusion increased significantly in spinal cord-injured participants, mirroring effects seen in healthy volunteers. Capsaicin altered the response in healthy subjects, producing contralateral increases in perfusion after cold immersion, but this shift did not occur in two spinal cord-injured patients who received capsaicin. Supported by a skin biopsy from a healthy participant, the investigators propose that peripheral C-fiber cross-talk contributes to an ipsilateral pathway that can partially bypass the spinal cord. This mechanism may help explain clinical phenomena such as referred itch and jogger’s migraine, and it suggests the possibility of training people with spinal cord injury to use facial cues as indicators of lower-limb sensory events.