There are no clear research results to date on the processes in the brain which can also be responsible for the occurrence of depression. It is certain that processes in the brain change during a depression. For example, changes can be seen in the sleeping-waking rhythm or in the release of hormones.
It is becoming increasingly clear to scientists that certain disturbances in the metabolism of the brain are biological factors which can decide whether a person becomes depressive and how high the risk of a new depressive episode is after recovery from a depression. But a comprehensive explanation has not yet been found.
It is assumed that certain messenger substances (neurotransmitter) in the brain – serotonin and noradrenaline – play a part in the occurrence of depression. Many scientists assume that a low serotonin level in the brain can help to trigger off depressions. Serotonin and noradrenaline play an important role in the transfer of information from one nerve cell to the next (see diagram). When the transmission of information is disturbed - because for example the body is producing too little serotonin or noradrenalin – this can effect the feelings, thoughts and behavior of the affected person. Depression or depressive moods are a possible consequence. At this point antidepressive medication is given in order to restore the balance in the brain metabolism.
A further explanation for the effect of brain processes on the occurrence of depression is connected with the stress hormone cortisol. It is assumed that depressive patients produce too much cortisol and are consequently in a kind of permanent stress.
