Can you imagine being unable to stop moving graciously? Imagine that every attempt to halt your walking or running was like smacking into a wall or stumbling to a halt ? Kind of like that amateur driver who uses no grace or finesse, every start is a stomp on the gas and every stop is a slamming on the brakes. Or can you imaging suffering from FOG (freezing of gait) as in some Parkinson’s patients ?
When we are healthy, we take locomotion for granted. When we are in pain, movement can become labored and challenging; when we have a neurologic disease to the locomotor centers, we can find it almost impossible. On occasion, it can be the seemingly simplest of things that can cause the greatest of difficulties, for example, we take stopping for granted and we underestimate the complexity of initiating movement. It is one of those things in life, you do not know what you have until you lose it. When was the last time you even thought about starting or stopping your movements ? It is so natural that the thought doesn’t even reach the surface of our conscious thought. When was the last time you walked towards your kitchen sink to wash the dishes and you consciously thought,
“ok, we are about 3 more steps from the sink, you had better slow down … . ok, 2 more steps … 1 more step, this is the last one … . ok, that is it, you have arrived at the sink, both feet stop moving … . . initiate double stance support, 50% weight on both feet… . . begin standing mode.”
There is a brainstem pathway specifically dedicated to control locomotor arrest. Activating this pathway stops locomotion, while inhibiting the pathway enables locomotion.
In the study below, researchers Julien Bouvier and Vittorio Caggiano together with Professor Ole Kiehn and colleagues studied how the complex brainstem neuronal circuits control locomotion in mice. What they found was this,
Neuronal populations in the Reticular Formation of the brain “constitute a major excitatory pathway to locomotor areas of the ventral spinal cord. Selective activation of these neurons (V2a) of the rostral medulla stops ongoing locomotor activity, owing to an inhibition of premotor locomotor networks in the spinal cord. Moreover, inactivation of such neurons decreases spontaneous stopping in vivo. Therefore, the V2a “stop neurons” represent a glutamatergic descending pathway that favors immobility and may thus help control the episodic nature of locomotion.”-Bouvier et al.
Human locomotion is an extremely complex task. It is one that requires all sensory and motor pathways to be intact and reflexive controls such as central pattern generators to function properly. Gait is a complex task that requires synchrony, rhythmicity, balance, coordination, endurance and strength to name a few. Initiating gait is highly complex, as is arresting one’s gait. We take for granted how complex these task are at coordinating muscles, joints, limbs, vision, proprioception, vestibular inputs and many other components not to forget the cerebral connection bring it all together to get us from one place to the next is a safe fashion. It is only when things go wrong that we realize how fragile, and how complex, the system truly is. Don’t believe us ? Well then, try to over ride the system next time you are coming to a curb at the corner of the busiest street in your town. Try to over ride the coordinated stop mechanism that enables you to suddenly stop perched on the curb, observing oncoming traffic, standing safely without falling into the lane.
Shawn Allen, one of The Gait Guys
“Descending command neurons in the brainstem that halt locomotion” by Julien Bouvier, Vittorio Caggiano, Roberto Leiras, Vanessa Caldeira, Carmelo Bellardita, Kira Balueva, Andrea Fuchs, and Ole Kiehn in Cell. Published online November 19 2015 doi:10.1016/j.cell.2015.10.074
This brief blog post was inspired from this article on the same topic. http://neurosciencenews.com/v2a-neurons-locomotion-neuroscience-3119/