Research confirms that there are mice who have delicate personalities and those that are the tougher type, just like humans. There are mice who when confronted with situations that are stressful, adopt an active strategy and attempt to tackle their problem, while some will only display an attitude that is passive. The more vulnerable type are those that are passive and their physiology resembles those that are linked to human depression.
Mice are exceptionally territorial and you will find one female living with five males. The only one who will mate with the female is the mouse who has gained control of all the resources from the beginning. Although the mice may fight amongst themselves, the same mouse will always win. He then takes possession of everything and the other mice suffer chronic social stress which is induced by defeat. Some become ill while others do not, proving that all are not equally affected. It all depends on how each individual mouse will react to stress.
Stress is related to a psychological disorder, but not all will develop this disorder. This is dependent on the behavior of the mouse when confronted by stress. If the dominant mouse had to attack, the passive dominated mouse would not even move, but the active mouse would run away. In a stressful situation we find the passive mouse remaining in a still position all the time and becoming even stiller. The active mouse is quite aware of the difficulty of the stress and that it is trapped in this situation, but nevertheless will put up more resistance. Interactions with the group leader are also different. While the passive mouse will not even look at the leader, the active one is interested and will sniff at it and attempt interaction. These are similar to the attitudes that humans display.
Research has confirmed that the clinical state of the passive mice can be compared to chosen strategy and that of human depression. The physiological display can be linked and compared to that of humans faced with stressful situations. Because all are stressed but not all become ill, the passive strategy makes one far more vulnerable and likely to illness. The practical implications could be enormous, in that if the perception is altered, the results may be huge. If the physiological mechanisms are also revealed, treatments for certain types of illness can be more specialized. These studies could prove to be a huge breakthrough for humans in instances of depression and other illnesses.