2 Neuroscience2.7 Neural circuits

2.7.2 Default mode and salience networks

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Written by Resident Doctor Committee · Published

Identifying networks at rest

  • Resting-state functional connectivity correlates the blood-oxygen-level-dependent (BOLD) signal between regions when no task is set, often using fluctuations below about 0.1 Hz.

  • A functional network is a set of separate regions whose activity rises and falls together. The correlation does not show a direct pathway, causal influence or which region leads.

  • Seed analysis maps correlation with one chosen region, whereas independent component analysis extracts recurring patterns without a seed.

The default mode network

Node

What it does

Medial prefrontal cortex

Self-evaluation and rumination

Posterior cingulate cortex

Core hub for self-reflection, autobiographical memory and the unified first-person sense of self

Precuneus

Posterior medial parietal hub, part of the default mode and not the salience network

Angular gyrus and inferior parietal lobule

Lateral parietal nodes

Parahippocampal gyrus and medial temporal lobe

Supply episodic detail

  • The posterior cingulate is the hub linked to depersonalisation, while the medial prefrontal hub is linked to rumination.

  • The network is most active during internally directed, self-referential thought: introspection, mind-wandering, autobiographical recall and future simulation.

  • It is task-negative: it is active at wakeful rest and deactivates below resting level during effortful, externally directed tasks, while task-positive networks activate.

  • Internal versus external focus matters more than task versus rest, so internally focused tasks can activate it.

  • In schizophrenia there is reduced task-induced deactivation: the network is suppressed less than normal during an external task, which reflects poor switching from internal to external attention.

The salience network

  • The salience network switches the brain between the default mode and task-positive networks.

  • The anterior insula is a hub that integrates interoceptive, sensory and emotional signals.

  • The dorsal anterior cingulate cortex is its medial partner and monitors conflict and errors.

  • Von Economo neurons cluster in these two hubs.

  • The amygdala adds learned significance, and the thalamus and striatum contribute state, value and learning.

  • Salience means relevance to goals or bodily needs, whether the cue is external or internal, such as pain.

The central executive network

  • The central executive (frontoparietal) network holds and manipulates information online, with the dorsolateral prefrontal cortex and intraparietal sulcus as its nodes.

  • Dorsolateral prefrontal underactivation in schizophrenia is the classic hypofrontality finding.

The triple network model

Menon's triple network model proposes that the salience network leads switching between the default mode and executive networks. An alarm, for example, interrupts internal planning and recruits executive action to find an exit.

The salience network (insula and anterior cingulate) sits above and switches between the default mode network (mPFC, PCC) and the central executive network (DLPFC, posterior parietal cortex), whose activity is anticorrelated. Nekovarova, Fajnerova, Horacek, Spaniel, CC BY 3.0, via Wikimedia Commons

  • Insular activity may precede a switch, but the timing does not prove causation.

  • Network findings shared across diagnoses are not specific biomarkers, and motion, wakefulness, symptoms and medication all alter them.

Revision material for the MRCPsych examinations. Not clinical guidance, and not for use in patient care.