Walking seems to be one of the most natural of movements. Yet, neuroscientists have struggled for decades to understand how our nervous system coordinates the complex interplay of nerves and muscles that structures locomotion.
Until recently, researchers assumed that a large diversity of neuronal circuits in the brain are responsible for handling this process. However, a new study led by Columbia University has found that a single type of neurons – the ventral spinocerebellar tract neurons – are completely responsible for keeping our legs in lockstep.
“As one might expect, it’s the brain that initiates locomotion. But it doesn’t coordinate it,” said study senior author George Mentis, a neuroscientist at Columbia University who investigates the neural circuits controlling walking in order to find new treatments for patients with health conditions such as spinal cord injuries, amyotrophic lateral sclerosis, or spinal muscular atrophy.
According to Professor Mentis and his colleagues, the coordination of our numerous walking muscles is handled by neurons in the spinal cord. If these ventral spinocerebellar tract neurons were silenced in freely moving adult mice, the animals could not move properly.
Furthermore, if the neurons were activated by light or drugs, they could reliably induce locomotor behavior in juvenile mice. “In other words, these neurons are both necessary and sufficient for locomotor behavior,” said Mentis.
The researchers also discovered that these neurons are highly interconnected, a feature which likely contributes to their capacity to generate the complex rhythmic patterns sustaining locomotion.
These findings could have important applications in medicine, by helping develop novel treatments for patients with motor disorders or spinal cord injuries.
“For example, it may not be enough to reconnect the brain and the spinal cord in people with severed spinal cords,” explained Mentis.
“Our findings suggest that you would also have to restore proper activity in the ventral spinocerebellar tract neurons to ensure that the central pattern generator is working properly. Everything has to be tightly balanced between exciting certain neurons and inhibiting others. If this balance is compromised, you won’t have coordinated movement.”
The study is published in the journal Cell.