The ‘default mode network’ (DMN) is a relatively new concept in the study of mental disorders, notably major depression, but also in other afflictions. It was first described in 2001, by the group of Raichle et al; and from thereon others took it up in further research.
I won’t make it too complex the first time around, but since it is so catchy and understandable for people who know firsthand what mood disorders are, I will briefly introduce it here. People who suffer from OCD, or schizophrenia (SCZ), or major depressive disorder (MDD), share commen characteristics, apart from specific features that separate these illnesses from each other.
One problem is: to be task-oriented, which means being able to plan properly, to make a reasonable assessment of the risks and benefits inherent in a certain strategy (execution of a task); and to be flexible enough to change over to an altered, or a entirely new strategy to reach a goal. OCD is notorious for its characteristic termed ‘catastrophic thinking’; that means that there is a gross overestimation of the chance for a bad outcome of a certain way of acting to reach a goal. The net result is often: a depressed mood, and procrastination, and fear, doubt and guilt are felt too.
These feelings are shared by people with major depression and schizophrenia. Now, although the patients may well be awake and alert, they tend to ‘look inward’, and ruminate about themselves. Not because they find themselves so important, but because this state is the natural outcome of a bad mental disorder. People who feel important are known for acting, wanting to make an impression on others, to guide, rule, and reign, and they tend to overestimate the quality of their performance.
Being forced to look inward, as a result of illness, isn’t anything nice or funny. You are caught in circular forms of negative thinking about yourself, and the longer this type of thinking occurs, the more negativity is there.
The idea now is that the patients I write about suffer from overactivity of the ‘default mode network’ in their brain, a set of brain tissues that is highly intriguing, because, with a lot of caution, we may postulate that if something like a ‘self’ can be located in the brain, this network of neuronal tissues is a candidate. Do I contradict myself here? Partially, for sure. Because I believe that older ideas about the location of consciousness, a self, a soul were much too pretentious. I tend to adhere to the idea of a neuronal/bodily/environmental ‘wholism’ – if you isolate a part of this complex, that part can’t be properly said to ‘contain the self’; it is merely a piece of gray tissue (in case of the brain), that doesn’t have a function in its isolated state.
But, in a much more modest sense, the idea of ‘inward looking’, and ‘depressed and reflective moods’ being linked somehow to the aforementioned default mode network is appealing.
Suppose other brain systems, needed to be active, to complete a given task in a given time frame, have their deficits. They can’t be task-oriented in the normal way, for instance because of catastrophic thinking. The patient remains passive. What happens then? Well, the default network takes over, and does what it is required to do in any normal person too: offer the possibility for reflection. Only thing is: that reflective process lasts too long and is therefore deleterious to the sanity of the patient. A balance has become tilted too much in one direction.
Health requires, as we intuitively feel, the opportunity to ‘lose ourselves’ in work, in loving and fruitful contact with others, and in hobbies. We cannot be obsessed with ourselves all of the time. ‘Lose ourselves’ is a beautiful apt phrasing here: the default network, connected with the notion of ‘self’, should be laid to rest very frequently, so that we can immerse ourselves in activities outside ourselves. But in mood and anxiety disorders it is precisely the capacity for being healthily task-oriented, and to ‘do’, that is frustrated.
I hope I could explain a bit about that default mode network, and why over-activity of it is strongly associated with mood disorders.
Obsessive-Compulsive Disorder 