July 7, 2019
Pondering Postural Control: The Vestibular System
Don’t tell the other sensory systems but the vestibular system is my favourite. This system is the one that piqued my interest years ago, the one that began my journey to understanding more about the connections between the dynamic nature of the sensory systems and postural control, the one that still challenges me in the clinic.
So why is this system so important? Well, there are several fascinating reasons:
- One of the descending pathways, the lateral vestibulospinal tract (LVST), contributes to the muscle tone of the anti-gravity extensors of the trunk and legs. Therefore, it is key to our upright posture.
- Another descending pathway, the medial vestibulospinal tract (MVST) provides reflexive control of the head and neck muscles. This is an integral piece of stabilizing the head on the body and therefore, contributes to gaze control.
- The vestibular system is intimately connected to the oculomotor nuclei to create gaze stability while our head is moving, through the vestibulo-ocular reflex (VOR). The VOR allows our eyes to maintain fixation on an object while participating in complex movement such as running, skiing and hockey. But it also helps us navigate obstacles as we walk across a room.
- The vestibular system is the one which provides us with our gravitational referent = our “which way is up” sense. This information is essential for both the stability and orientation components of postural control.
- The vestibular system informs the respiratory diaphragm (remember the vestibulorespiratory reflexes we studied in cardioresp?). This is a crucial connection between the vestibular system and anticipatory postural control.
- The vestibular system contributes to our body schema which subsequently impacts our stability limits.
- Finally, this system also plays a part in emotional arousal and regulation, because of it’s connections with the limbic system.
Most of my clients do not have difficulty with the peripheral sensory receptors of the vestibular system. One exception to this is children with CHARGE syndrome who have small/absent the semicircular canals. However many of our clients do have difficulty with the central processing of vestibular input. So how do we assess vestibular function in the clinic? We have to do so indirectly. In my assessment, I note if a child has issues with low tone – an indication that the vestibular system may be involved. I also look at the quality of head and trunk righting and equilibrium reactions; all of these are informed by vestibular input. I also look at the quality of trunk rotation and bilateral integration in movement. Further unstructured observations are helpful. Does the child climb on equipment? Do they like to hang off the equipment, hang upside down, are they fearful of uneven/unstable surfaces? One can also assess post-rotary nystagmus (PRN). Testing PRN occurs for 10 rotations at 1 rotation per 2 seconds, testing both clockwise and counter clockwise. Normal PRN lasts for between 12 and 28 seconds, although it may be slightly less in younger children (Rine, Introduction to Paediatric Vestibular Rehabilitation, 2014). Therapists who have training in paediatric vestibular rehabilitation, or the Sensory Integration and Praxis Test (SIPT) or the Astronaut Training program will be familiar with this test. Balance testing using the CTSIB is also be helpful. Finally I note if there are difficulties with emotional regulation during the session/transitions and any pattern to these difficulties. None of these is definitive, but put them all together and they do give an indication of how well vestibular system information is being integrated for function.
There is documentation in the literature regarding vestibular deficits in children with CP. Vestibular over-responsiveness and vestibular under-responsiveness patterns are well documented in the literature addressing children with sensory processing challenges and children with ASD.
In my experience successful treatment of central vestibular challenges requires a grounding in both sensory processing and sensory integration theory and techniques. Children who are over-responsive may:
- be fearful of moving equipment
- be fearful of simple challenges to balance
- may appear lethargic
- may appear to have low muscle tone
- may avoid active play
Children who are under-responsive may:
- appear to need to move
- enjoy busy, energetic activities
- appear to be in constant motion
- spin, whirl, or bounce frequently
You can begin with gentle, more linear movement (using a rocking chair, suspended equipment or bouncing on a ball) and observe the child’s responses to this input; steer clear of the more intense, rotational input when you are beginning your learning. Children who are over-responsive may tolerate just a little bit of vestibular input, children who are under-responsive may seek more. Vestibular input is powerful, as this system talks to many other parts of the brain, so grade the input carefully. If the child asks to discontinue the activity, the therapist should honour this. As you provide the movement, you need to keep a close watch on the autonomic system for signs of overload:
- irregular breathing
- colour change
- sweating, pallor
- hiccups, yawning
- increased anxiety
- change in sleep patterns
If you notice a child having difficulty with vestibular input, deep pressure can help reorganize the systems (ex. firm hugs, wrapping in tight in a stretchy blanket). After providing vestibular input, we need to use it! Help the child/set up the environment to move more efficiently against gravity, balance with control, combine movement and vision in function – whatever your goal is, put it into practice. This is the beginning of integrating sensation and movement for function.
There are lots of resources regarding the vestibular system. If you want to read more, you can start here. Next up on Pondering Postural Control is the Vestibular System’s BFF, the Proprioceptive System.