Resting State Morteza Ansarinia Institute for Cognitive Science Studies January 2017

★ Introduction ★ Default Mode Network ★ Functions of DMN ○ Sentinel Hypothesis ○ Internal Mentation Hypothesis Outline

★ When we lie down in a quiet room, and 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

★ In resting state paradigms, participants are merely asked to 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

★ When a person engages in a perceptual behavioral task, 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

Top: Slow fluctuations are correlated between mPFC and cingulate cortex. Middle and Bottom: areas colored blue and green were more active during quiet rest periods that during the behavioral task.

★ The default mode network is known to be involved 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

Default Mode Network Attention/Control Network

Theories Sentinel Hypothesis Even when we rest, we must broadly 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.

★ Decreases from DMN activity are less when a person 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

★ Brain activity in autobiographical memory tasks is increased compared 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

Subjects were asked to recall a past event or imagine an event in the future. Similar posterior cingulate and mPFC components of the DMN were activated in the autobiographical memory tasks.

Development of correlations between brain networks Frontal DMN

Bear, MF, BW Connors and MA Paradiso (2015). Neuroscience: Exploring the Brain. 4th Ed., ISBN-10: 0781778174, Chapter 21. References Thank You :-)