Vestibular sense
This is the first of the senses that is not commonly known at all. If it was, it would be known as our sense of balance and spacial orientation. The vestibular sense is the system that interprets information about our environment and our body position to facilitate posture, movement, coordination, and position in the environment. This sense is supported by our environmental senses and is one of multiple senses that help us to move our bodies appropriately. There are different aspects to the vestibular sense.
Vestibular sense function
Experience from the vestibular system is called equilibrioception.
Self motion
When the vestibular system is stimulated without any other inputs, one experiences a sense of self-motion. For example, a person in complete darkness and sitting in a chair will feel that he or she has turned to the left if the chair is turned to the left. A person in a lift, with essentially constant visual input, will feel they are descending as it starts to descend. There are a variety of direct and indirect vestibular stimuli which can make people feel they are moving when they are not, not moving when they are, tilted when they are not, or not tilted when they are. Although the vestibular system is a very fast sense used to generate reflexes, including the righting reflex, to maintain perceptual and postural stability, compared to the other senses of vision, touch and audition, vestibular input is perceived with delay.
Common experiences of motion are swinging, twirling, jumping, climbing, rolling, and dancing.
Balance and spatial awareness
Although we may not be consciously aware of our vestibular system’s sensory information under normal circumstances, its importance is apparent when we experience motion sickness and/or dizziness related to infections of the inner ear (Khan & Chang, 2013).
In addition to maintaining balance, the vestibular system collects information critical for controlling movement and the reflexes that move various parts of our bodies to compensate for changes in body position.
Bilateral coordination
Vestibular sensing also supports the proper development of bilateral coordination; the ability to coordinate both sides of the body at the same time in a controlled and organised way. A good example of this is stabilising paper with one hand and cutting with the other.
Good bilateral integration is an indicator that both sides of the brain are communicating effectively and sharing information, and is important for many aspects for learning and development.
Understanding kinaesthesia and proprioception
Kinaesthesia is often either ignored, or mistaken for vestibular or proprioceptive senses. Kinaesthesia requires the combined input from both the vestibular and proprioceptive systems, and all three must be combined with our capability to physically use our body. In fact, kinaesthesia is one type of interoception (a tactile type) rather than either of these; it is the interpretation of messages from things like stretch and tension in muscles, joints and tendons when we move, and combined with our senses of balance, spacial awareness, orientation, and the edges of our body (proprioception), we are able to move and coordinate ourselves.
Vestibular sense regulation
As human beings we need to have time when we can rest these senses and be happily stationary, but we also have a deep need to gain input from these senses. For regulation, we need to move, as we would have naturally spent most of our days moving in various ways such as large amounts of walking, some climbing, and potentially hanging and pulling ourselves up with our arms. Humans can become unsettled if they do not get enough vestibular input, and this is particularly relevant in small children.
Identifying vestibular hyper-sensitivity
People who experience vestibular input more intensely or who have a low need for vestibular input, avoid stimulation and may:
- Seem sedentary
- Be overly cautious
- Avoid movement in multiple ways
- Be labelled as lazy
- Suffer from motion sickness
- Prefer lying down to sitting up, and leans or lies on arms
- Experience gravitational insecurity (fearful of heights, feet leaving the ground, moving backwards, uncomfortable with their feet unsupported when sitting).
Identifying vestibular hypo-sensitivity
People who experience vestibular input less intensely or who have a high need for vestibular input, crave movement and sensory stimulation. They may:
- Be thrill seekers
- Enjoy spinning and do not easily become dizzy
- Love swings, and like to swing as high as possible
- Appear to be clumsy, tripping and falling often
- Easily lose their balance when trying to ride a bike or when climbing stairs.
- Often sits upside down, chooses to roll around, or jump and fall from high places
- Be easily disoriented when bending down, getting up, or changing direction
Vestibular neurobiology
The cochlea
The cochlea is part of the auditory system, and so you will have read about it before. It is found in the labyrinth of the inner ear and are fluid-filled and have hair cells, similar to the ones found in the auditory system, which respond to movement of the head and gravitational forces. When these hair cells are stimulated, they send signals to the brain via the vestibular nerve.
Vestibule-ocular reflex (VOR)
The vestibular system sends signals primarily to the neural structures that control eye movement; these provide the anatomical basis of what is known as the vestibulo-ocular reflex. The VOR is a reflex that stabilises images on the retina during head movement, by producing eye movement in the direction opposite to head movement, therefore preserving an image in the centre of the visual field.
A good example of this is when the head moves to the right, the eyes move to the left, and vice versa. Since slight head movements are present all the time, the VOR is very important for stabilising vision; patients whose VOR is impaired find it difficult to read, because they cannot stabilise the eyes during small head tremors. The VOR reflex does not depend on visual input and works even in total darkness or when the eyes are closed.
