Habituation exercises
The goal of the habituation exercise is to lessen the uncomfortable response to a specific, provoking stimulus. The provoking stimulus could be different between people, but mainly they involve head motion or complex visual environments. Other provoking stimuli include bridges, patterns or heights. Below is an example of a visually complex scene that might provoke some people.
Habituation programs should start with an assessment of the provoking stimulus. The effect of the stimulus can be measured via balance force plate, and subjective symptoms can be recorded in terms of intensity and duration.
The concept behind habituation exercises is to slowly and gradually improve the brain’s ability to “process” the stimulus. One way to think about this is to use the analogy of strength training. That is, to strengthen a muscle, the resistance must be challenging but not overloading. If the challenge is gradually increased over time, it is likely that the muscles will adapt by becoming stronger. The same may be true for the brain.
It is important that the challenge is an “appropriate” load, whereby there is some provocation of symptoms, but these symptoms return to baseline after each repetition. The duration of the stimulus exposure, the intensity of the challenge and the rest between repetitions can all be modified to progress the challenge. By increasing the challenge to the brain, it is predicted that the provoking stimulus will become easier to process, and symptoms will improve.
Gaze stabilization
The vestibular system is a complex collection of brain regions, including part of the inner ear, the brainstem and the higher regions of the brain. The vestibular sensors in the inner ear are able to detect movement of the head, and with this, the brain is able to send messages to the eyes. The main purpose for this reflex, called the vestibular-ocular reflex (VOR) is to enable the eyes to stay fixated on a target. As can be seen in the diagram below, the eyes and head are both in the neutral position in (A), but then as the head rotates right the eyes move left (B) and as the head rotates left, the eyes move right (C) . This is a normal VOR function.
Fortunately, if the VOR is somewhat dysfunctional another part of the brain called the cerebellum is able to recalibrate the reflex so that the brain is still able to give the eyes the correct instructions.
Gaze stabilisation exercises are tapping into this cerebellum’s unique ability to adapt! It is important when doing gaze stabilization exercises that the head movement is in the correct direction, and at the correct speed. If the speed is too slow, there is no reason to prompt adaptive change, and therefore the brain will not improve.
Despite the need for these exercises to be done at a relatively high speed, it is also important that the gaze stability exercises do not irritate neck problems, nor do they increase the symptoms of headache. Some people recovering from concussion may find that gaze stability exercises provoke their symptoms, in which case they are not appropriate at the time.
