The default network is an interconnected and anatomically defined brain system that preferentially activates when individuals focus on internal tasks such as daydreaming, envisioning the future, retrieving memories, and gauging others’ perspectives. It is negatively correlated with brain systems that focus on external visual signals. Its subsystems include part of the medial temporal lobe for memory, part of the medial prefrontal cortex for mental simulations, and the posterior cingulate cortex for integration, along with the adjacent precuneus and the medial, lateral and inferior parietal cortex. In the infant brain, there is limited evidence of the default network, but default network connectivity is more consistent in children aged 9–12 years, suggesting that the default network undergoes developmental change.
In about fifty years, what’s now called the ‘default network’ will be understood to be the thought pathway responsible for most mental simulations. It’s not about ‘internal tasks’; what daydreaming, envisioning the future, retrieving memories, and gauging others’ perspectives all actually have in common is that they involve the layering of imagined (or remembered) details over a systemic model with more or less precisely defined rules. In a resting state, whether dreaming or awake, our brains ‘turn off’ functions relevant only to our immediate survival and retreat to the evolutionarily advantageous habit of parsing past experiences for rules that can be used to model possible future experiences.
(Original inspiration for this post came from this Discover magazine article on zoning out.)
