Hypothalamic dysfunction Control of serotonin and of stress responses occurs in the hypothalamus. It may be that people with anorexia have an innately malfunctioning hypothalamus. The hypothalamus controls the autonomic nervous system (mediates emotion) and the endocrine system (governs hormones, such as those for menstruation). It is also involved in the control of hunger and satiety – the lateral hypothalamus produces feelings of hunger whilst the ventromedial hypothalamus suppresses hunger. Humans (and other animals) have a ‘set weight’ that is correct for them and anyone who falls below this weight will feel hungry. Anyone who goes above it will eat less in order to regain their ‘normal’ weight so that when satiety is reached, eating becomes aversive.
Normally, when individuals begin to starve, neurochemical signals of hunger are elevated and signals for satiety and activity are lowered. It’s suggested that dysfunction of these hypothalamic brain regions can lead to anorexia. Neuromodulators and hormones influencing hunger, satiety, and activity may be present in unusual concentrations in anorexics that are opposite to those found in normal starvation. This is consistent with anorexic patients’ descriptions of their subjective experience of finding it very difficult to eat and feeling restless and driven to exercise.
Dopamine - It has been suggested that anorexia can be explained by over activity in dopamine receptors in the part of the brain known as the basal ganglia (where dopamine plays a part in the interpretation of harm and pleasure). Dopamine regulates the pain-pleasure pathways so if the receptors are overactive it may confuse the 2 emotions and lead to sufferers not being able to distinguish pleasurable activities such as eating, leading them to not eat and lose weight, resulting in anorexia. Increased dopamine activity in the mesolimbic pathway may change the way that people interpret rewards and that individuals with anorexia may find it difficult to associate good feelings with the things most people find pleasurable, such as food.
Serotonin – It has been suggested that serotonin acts to suppress appetite and therefore disturbances in the level of this neurotransmitter may be a characteristic of individuals with eating disorders. In particular, it seems that increased serotonin activity in the brain may be responsible for anorexic behaviour via appetite suppression (and is also associated with increased anxiety, obsessive behaviour and vomiting – all characteristics of anorexia). Restricting food intake may decrease serotonin levels (in particular a substance called tryptophan) so people with anorexia may feel better starving themselves.