Stereotypic behaviour can be elicited by many causal factors at different levels. Stereotypies is typically elicited by limitations in space or behavioural possibilities at the Environmental level; by altered conditions or states at the Physiological level (Induced by factors at the Environmental level or by injection of various pharmaca) and might possible depend of how the organism is equipped on the Genetic level.
A Sketch is seen in Figure 1 in which only a few important factors/pathways is indicated.
Figure 1:
Of these, it can briefly be mentioned that the central nervous system (CNS) off course is monitoring the surroundings and if these are adversible to the animal it can subsequently lead to an increased activation of adrenal hormones, of which one (Cortisol/Corticosterone), has an effect at the Genetic level influencing which mRNA will be produced.
Different types of pharmaca is typically used to change local concentrations (or effective levels) of transmitter substances in the brain (e.g. Dopamine, Serotonin, GABA and many more), but can be used too to induce brain lesions. More about that in a later chapter.
Outside factors, e.g. Scheduled feeding, can be causal in explaining the difference between certain species and their timing of stereotypies. This practice can be observed on farms and in stable milieus, and a behaviour rather similar to stereotypic behaviour can be initiated in experiments with Operant Learning. The resulting behaviour is named Adjunctive.
Briefly, Operant Learning is a procedure where a hungry animal is rewarded with small portions of food upon completion of certain tasks. These can e.g. be that the individual has to make a certain number of correct responses in order to receive a reward (the individual is said to be Reinforced), or the reward is given after a variable number of responses (however, the average number of responses will typically be set before the experiment). The experimenter can choose to reward the individual after a fixed (or variable) time or after intervals of time where a certain number of responses has been performed and so on. There are many variants within these procedures but the bottom line is that the animal often starts to develop adjunctive behaviours, which seem purposeless to the experimenter.
Situations wherein there is an element of inescapable fear or frustration combined with a stay in small barren cages without proper stimuli and isolated from other animals of its kind will typically induce stereotypic behaviour provided the specie is prone to do so.
Next topic: Hypothesis: "Genetically based differences among stereotypies".
