Default mode network

In neuroscience, the default mode network (DMN), also default network, or default state network, is a large scale brain network of interacting brain regions known to have activity highly correlated with each other and distinct from other networks in the brain. In neuroscience, the default mode network (DMN), also default network, or default state network, is a large scale brain network of interacting brain regions known to have activity highly correlated with each other and distinct from other networks in the brain. It was initially assumed that the default mode network was most commonly active when a person is not focused on the outside world and the brain is at wakeful rest, such as during daydreaming and mind-wandering. However, it is now known that it can contribute to elements of experience that are related to external task performance. It is also active when the individual is thinking about others, thinking about themselves, remembering the past, and planning for the future. Though the DMN was originally noticed to be deactivated in certain goal-oriented tasks and is sometimes referred to as the task-negative network, it can be active in other goal-oriented tasks such as social working memory or autobiographical tasks. The DMN has been shown to be negatively correlated with other networks in the brain such as attention networks. Evidence has pointed to disruptions in the DMN of people with Alzheimer's and autism spectrum disorder. Hans Berger, the inventor of the electroencephalogram, was the first to propose the idea that the brain is constantly busy. In a series of papers published in 1929 he showed that the electrical oscillations detected by his device do not cease even when the subject is at rest. However, his ideas were not taken seriously, and a general perception formed among neurologists that only when a focused activity is performed does the brain (or a part of the brain) become active. But in the 1950s, Louis Sokoloff and his colleagues noticed that metabolism in the brain stayed the same when a person went from a resting state to performing effortful math problems suggesting active metabolism in the brain must also be happening during rest. In the 1970s, Ingvar and colleagues observed blood flow in the front part of the brain became the highest when a person is at rest. Around the same time, intrinsic oscillatory behavior in vertebrate neurons was observed in cerebellar Purkinje cells, inferior olivary nucleus and thalamus. In the 1990s, with the advent of positron emission tomography (PET) scans, researchers began to notice that when a person is involved in perception, language, and attention tasks, the same brain areas become less active compared to passive rest, and labeled these areas as becoming “deactivated”. In 1995, Bharat Biswal, a graduate student at the Medical College of Wisconsin in Milwaukee, discovered that the human sensorimotor system displayed 'resting-state connectivity,' exhibiting synchronicity in functional magnetic resonance imaging (fMRI) scans while not engaged in any task. Later, experiments by neurologist Marcus E. Raichle's lab at Washington University School of Medicine and other groups showed that the brain's energy consumption is increased by less than 5% of its baseline energy consumption while performing a focused mental task. These experiments showed that the brain is constantly active with a high level of activity even when the person is not engaged in focused mental work. Research thereafter focused on finding the regions responsible for this constant background activity level. Raichle coined the term 'default mode' in 2001 to describe resting state brain function; the concept rapidly became a central theme in neuroscience. Around this time the idea was developed that this network of brain areas is involved in internally directed thoughts and is suspended during specific goal-directed behaviors. In 2003, Greicius and colleagues examined resting state fMRI scans and looked at how correlated different sections in the brain are to each other. Their correlation maps highlighted the same areas already identified by the other researchers. This was important because it demonstrated a convergence of methods all leading to the same areas being involved in the DMN. Since then other resting state networks (RSNs) have been found, such as visual, auditory, and attention networks. Some of them are often anti-correlated with the default mode network.