First hypothesis: "The function of Stereotypies is to up-regulate Arousal."
Lets assume the problem for the individual is that it is placed in circumstances, which leads to too low level of arousal. By engaging in stereotypic behaviours propio-receptors in muscles, joints and tendons is activated, by that increasing the levels of internal stimuli, by which the level of Arousal, according to the hypothesis, will be subject to an increase.
However, in reality there is not really any data in support of this hypothesis. It has still not been proven that the level of Arousal increases solely as a function of increased levels of internal stimuli thanks to the stereotypic behaviours, but do not despair - the complementary hypothesis is straightforward.
Second hypothesis: "The function of Stereotypies is to down-regulate Arousal"
Lets assume the problem for the individual on the contrary is that it experiences a too high level of Arousal. In such a case it can take advantage of the fact that a given brain has a fixed Bandwidth (a digital expression), which makes it possible for it only to process (yet a digital expression) a certain amount of information at the same time. Engaging in stereotypic behaviour increases the amount of internal stimuli, which then will overshadow the amount of aversible external stimuli.
Other available data could indicate that an Arousal down-regulation as a consequence of stereotypies could indeed be the case.
* A study testing normal children, often performing stereotypic leg swings, showed a correlation between these stereotypies and a lowering of the pulse.
* Autistic children with bouts of stereotypies display, during these stereotypies, a more variable (de-synchronized) heart rhythm, which, among others, is associated with REM-sleep.
* Stereotypies in these autistic children typically display an increased frequency as a response to increased complexity in their surroundings; introduction of foreign objects or -people, just as an electroencephalogram (EEG) recorded at the same time shows more de-synchronized brain waves.
A common observation regarding stereotyping animals is that they seem less attentive towards the surroundings while engaged in stereotyping, but some dangerous exceptions has been known to occur. Especially bears seem generally very aware on their surroundings and it has been observed how one of these terminated its pacing the instance a spectator dropped a leaflet (from a tree) into its enclosure.
* However, certain results do contradict this hypothesis, e.g. the fact that high arousal can reduce the amount of stereotypies. Pharmaca-induced stereotypies too can be reduced if the individual is affected by outer (environment) stressors.
The researchers spend many years debating whether stereotypies served the purpose of either Up-, or Down regulate Arousal until the day one of them made an " Egg of Columbus ":
Third hypothesis: "Stereotypies could serve a Homeostatic function. In circumstances where the level of Arousal was too low this was up regulated and vice versa.
The relevance of these hypotheses is still unclear. Related to the concept of Arousal is another concept - Coping - which will be mentioned since it has caused yet a much debated hypothesis.
Next topic: The concept of "Coping". Hypothesis: "Stereotypies is a Coping strategy".