close our eyes (but still awake), what is going on in our brain? ★ When the brain is imaged with PET or fMRI, it is found that its resting state activity includes regions that really are quiet and others that are surprisingly active. Introduction
lie back and rest. ★ In the absence of a task, the fluctuations in brain activity are little more than noise. ★ In brain regions that are functionally connected the noise levels tend to correlate together. ★ These spatially separated regions tend to be more active when not engaged in an experimental task. ★ Differences in operation and construction of this network are found in various conditions such as schizophrenia and autism. ★ It is reasonable to assume that resting state generally consists of some kind of inner thought rather than absence of cognition. Introduction
there are decreases in the activity of some brain areas at some time that task-relevant brain areas become more active. ★ DMN is a network of brain regions that are active when the brain is at rest. ★ Characterized by coherent neuronal oscillations at a rate lower than 0.1 Hz. ★ DMN includes: ◦ Posterior Cingulate Cortex ◦ Adjacent Precuneus ◦ Medial Prefrontal Cortex ◦ Medial, Lateral, and Inferior Parietal Cortex Default Mode Network DMN Connectivity
in many seemingly different functions: ◦ Autobiographical information, episodic memory ◦ Self-reference ◦ Emotion of one’s self ◦ Theory of mind ◦ Emotions of other ◦ Moral reasoning ◦ Social evaluation and categorization ◦ Remembering the past, imagining the future ◦ Story comprehension DMN Functions
monitor (pay attention to) our environment. In comparison, when we are active, we focus our attention on the matter at hand. Evolutionarily we may have evolved to be always “on the lookout.” Internal Mentation DMN supports thinking and remembering, the sort of daydreaming we do while sitting quietly. During resting, we silently recall past events in our lives or imagine an event that might happen to us in the future.
switches from rest to a peripheral vision task than from rest to foveal vision task. ◦ At rest we always diffusely monitor our broad visual field. Thus, there is less change from sentinel activity to an active task involving peripheral vision. ◦ DMN became activated when people were required to broadly monitor their peripheral vision, but not when they were instructed to focus on one location. ★ Evidence from simultagnosia: people have normal visual fields are are able to perceive objects, but are unable to integrate complex scenery. ◦ Posterior cingulate cortex may play a role in diffusely monitoring the visual field for stimuli. Sentinel Hypothesis
to when tasks involved the simple use of facts. ★ Hippocampus and neocortical areas in the DMN become more active. ★ Recalling past events and imagining new ones activate similar regions of medial prefrontal and posterior cingulate cortex. Overall Hypothesis When the situation requires us to become actively involved in a perceptual or motor task, we switch modes from sentinel and internal mentation activities to focused processing of sensory input or motor output. Internal Mentation Hypothesis