Default Network - Function

Function

In humans, the default network has been hypothesized to generate spontaneous thoughts during mind-wandering and may relate to creativity. Alternatively, default mode activity may represent underlying physiological processes going on in the brain that are unrelated to any particular thought or thoughts. It has been hypothesized to be relevant to disorders including Alzheimer's disease, autism, and schizophrenia. In particular, reduced default network activity has been associated with autism, overactivity with schizophrenia, and the default network is preferentially attacked by the buildup of beta-amyloid in Alzheimer's disease. Lower connectivity was found across the default network in people who have experienced long term trauma, such as childhood abuse. Among people experiencing posttraumatic stress disorder, lower activation was found in the posterior cingulate gyrus compared to controls (Dr. Ruth Lanius, Brain Mapping conference, London, November 2010). The posterior cingulate gyrus discerns emotional and self-relevant information; this interacts with the anterior cingulate gyrus, which integrates emotional information with cognition; and the medial prefrontal cortex, which allows for self-reflection and the regulation of emotion and arousal. This appears to correlate with the experience of people who have experienced long-term trauma and describe feeling 'dead inside' or have a fragmented sense of self or enter dissociative states. Children who have been traumatised often lack an inner world of imagination and show little symbolic play, this too is likely to be due to interruptions across the default network. Meditation practice (including transcendental meditation) is recommended for reactivating these networks. Impaired control of entering and leaving the default network state is correlated with old age.

The idea of a "default network" is not universally accepted. In 2007 the concept of the default mode was criticized as not being useful for understanding brain function, on the grounds that a simpler hypothesis is that a resting brain actually does more processing than a brain doing certain "demanding" tasks, and that there is no special significance to the intrinsic activity of the resting brain.