Why Do We Get Dizzy?
What happens when it goes wrong?
If there is a disturbance in the semi-circular canals or the otoliths, then there is a mismatch between the input information from these five end organs when the head is moved or turned. The brain will interpret this mismatch as a sensation of rotation of the body or the environment. When there is damage to the otolith organ, then a sensation of tilt or a feeling that the body is moving through the environment, will occur. There are a number of other symptoms that can be generated by damage to the balance mechanism and these include a muzzy sensation, dizziness or a true vertigo, that is a hallucination of movement, together with nausea and/or vomiting.
Nausea, vomiting and the need to lie down are usually more marked with peripheral lesions of the balance mechanism rather than central lesions sitting within the brain stem.
Why do we get dizzy?
When we move our head normally, the eyes rotate opposite to the head. This in effect cancels the motion of the head. Ballet dancers, gymnasts and acrobats are the best at this. They are remarkably able to stabilise the image of what is going on around them within their retina. We manage to stabilise the image on the retina by what is known as the vestibulo-ocular reflex (VOR). This reflex means that the eyes rotate at the same speed as the head but in the opposite direction and this stops us having a blurring of the visual image which would be inevitable with head movement.
If we continue to move our head rapidly in the dark, the normal VOR will stop and the brain gets the false impression that there is not any movement. If vision is then restored, there will be a sensation of movement and in turn there is a subjective symptom of dizziness.
Vision itself can generate the VOR (this is known as optokinetic response). This may generate a feeling that there is movement when for instance we look out of a car or plane window and an adjacent vehicle starts to move.
With the eyes open and very rapid head movement, there will be a high volley or neural signals arising from the different structures. The visual signal however will take over the neural input as the vestibular mechanism tends to fatigue more readily in the normal state.
When the balance mechanism is damaged for any reason or if it is poorly trained or suffers as a consequence of prolonged recumbency or lack of use, then the imbalance between the visual pathway and the vestibular mechanism gets enhanced relative to the visual pathway. This means that there is a much greater vulnerability to the brain perceiving this imbalance as dizziness with even minor head movement rather than the rapid movement that would normally generate this.