The salience network (SN), also known anatomically as the midcingulo-insular network (M-CIN), is a large scale brain network of the

human brain The human brain is the central organ of the human nervous system, and with the spinal cord makes up the central nervous system. The brain consists of the cerebrum, the brainstem and the cerebellum. It controls most of the activities of ...

that is primarily composed of the

anterior insula The insular cortex (also insula and insular lobe) is a portion of the cerebral cortex folded deep within the lateral sulcus (the fissure separating the temporal lobe from the parietal and frontal lobes) within each hemisphere of the mammalian br ...

(AI) and dorsal anterior cingulate cortex (dACC). It is involved in detecting and filtering salient stimuli, as well as in recruiting relevant functional networks. Together with its interconnected brain networks, the SN contributes to a variety of complex functions, including communication, social behavior, and self-awareness through the integration of sensory, emotional, and cognitive information.Menon V. (2015) Salience Network. In: Arthur W. Toga, editor. Brain Mapping: An Encyclopedic Reference, vol. 2, pp. 597-611. Academic Press: Elsevier. https://med.stanford.edu/content/dam/sm/scsnl/documents/Menon_Salience_Network_15.pdf The network is detectable through

independent component analysis In signal processing, independent component analysis (ICA) is a computational method for separating a multivariate signal into additive subcomponents. This is done by assuming that at most one subcomponent is Gaussian and that the subcomponents ar ...

of resting state fMRI images, as well as seed based functional connectivity analysis. The functional connectivity has been linked with structural connectivity through

diffusion tensor imaging Diffusion-weighted magnetic resonance imaging (DWI or DW-MRI) is the use of specific MRI sequences as well as software that generates images from the resulting data that uses the diffusion of water molecules to generate contrast in MR images. It ...

, which reveals white matter tracts between the AI and dACC.

Anatomy

The salience network is primarily anchored at the AI and dACC. The node in the AI corresponds with the dorsal-anterior division distinguished in meta-analyses of

task-positive network The dorsal attention network (DAN), also known anatomically as the dorsal frontoparietal network (D-FPN), is a large-scale brain network of the human brain that is primarily composed of the intraparietal sulcus (IPS) and frontal eye fields (FEF) ...

related neuroimaging studies. The AI and dACC are linked via a white matter tract along the uncinate fasciculus. Other regions of the network may include the inferior

parietal cortex The parietal lobe is one of the four major lobes of the cerebral cortex in the brain of mammals. The parietal lobe is positioned above the temporal lobe and behind the frontal lobe and central sulcus. The parietal lobe integrates sensory inform ...

, right

temporoparietal junction The temporoparietal junction (TPJ) is an area of the brain where the temporal lobe, temporal and parietal lobe, parietal lobes meet, at the posterior end of the lateral sulcus (Sylvian fissure). The TPJ incorporates information from the thalamus a ...

, and lateral prefrontal cortex. The subcortical nodes have yet to be structurally linked to the AI and dACC, however both seed-based and resting-state studies have observed intrinsic connectivity of the cortical nodes, with subcortical nodes consisting of the sublenticular extended amygdala, the

putamen The putamen (; from Latin, meaning "nutshell") is a round structure located at the base of the forebrain (telencephalon). The putamen and caudate nucleus together form the dorsal striatum. It is also one of the structures that compose the basal ...

, the

ventral striatum The striatum, or corpus striatum (also called the striate nucleus), is a nucleus (a cluster of neurons) in the subcortical basal ganglia of the forebrain. The striatum is a critical component of the motor and reward systems; receives glutam ...

, the dorsomedial

thalamus The thalamus (from Greek θάλαμος, "chamber") is a large mass of gray matter located in the dorsal part of the diencephalon (a division of the forebrain). Nerve fibers project out of the thalamus to the cerebral cortex in all direct ...

hypothalamus The hypothalamus () is a part of the brain that contains a number of small nuclei with a variety of functions. One of the most important functions is to link the nervous system to the endocrine system via the pituitary gland. The hypothalamus ...

, and the

substantia nigra The substantia nigra (SN) is a basal ganglia structure located in the midbrain that plays an important role in reward and movement. ''Substantia nigra'' is Latin for "black substance", reflecting the fact that parts of the substantia nigra ap ...

ventral tegmental area The ventral tegmental area (VTA) (tegmentum is Latin for ''covering''), also known as the ventral tegmental area of Tsai, or simply ventral tegmentum, is a group of neurons located close to the midline on the floor of the midbrain. The VTA is the ...

. The salience network is also distinguished by distinct cellular components, including von Economo neurons in the AI/dACC. Cortico-striatal-thalamic loop circuits contribute to the salience network.

Function

While the function of the salience network is not exactly known, it has been implicated in the detection and integration of emotional and sensory stimuli, as well as in modulating the switch between the internally directed cognition of the

default mode network In neuroscience, the default mode network (DMN), also known as the default network, default state network, or anatomically the medial frontoparietal network (M-FPN), is a large-scale brain network primarily composed of the dorsal medial pref ...

and the externally directed cognition of the central executive network. Evidence that the salience network mediates a switch between the DMN and CEN comes from Granger causality analysis and studies utilizing

transcranial magnetic stimulation Transcranial magnetic stimulation (TMS) is a noninvasive form of brain stimulation in which a changing magnetic field is used to induce an electric current at a specific area of the brain through electromagnetic induction. An electric pulse gener ...

. The timing of electrophysiological responses during the oddball task is consistent with interaction, as after the initial mismatch negativity response is transmitted "bottom-up" from sensory regions, a "top-down" signal localized to the AI and dACC occurs before a widespread evoked potential that corresponds to attentional shifting. It has also been hypothesized that the AI receives multimodal sensory input and the ACC and the associated dorsomedial prefrontal cortex sends motor output.

Clinical significance

Dysfunction in the salience network have been observed in various psychiatric disorders, including

anxiety disorder Anxiety disorders are a cluster of mental disorders characterized by significant and uncontrollable feelings of anxiety and fear such that a person's social, occupational, and personal function are significantly impaired. Anxiety may cause phy ...

post-traumatic stress disorder Post-traumatic stress disorder (PTSD) is a mental and behavioral disorder that can develop because of exposure to a traumatic event, such as sexual assault, warfare, traffic collisions, child abuse, domestic violence, or other threats o ...

schizophrenia Schizophrenia is a mental disorder characterized by continuous or relapsing episodes of psychosis. Major symptoms include hallucinations (typically hearing voices), delusions, and disorganized thinking. Other symptoms include social w ...

frontotemporal dementia Frontotemporal dementia (FTD), or frontotemporal degeneration disease, or frontotemporal neurocognitive disorder, encompasses several types of dementia involving the progressive degeneration of frontal and temporal lobes. FTDs broadly present as ...

, and

Alzheimer's disease Alzheimer's disease (AD) is a neurodegenerative disease that usually starts slowly and progressively worsens. It is the cause of 60–70% of cases of dementia. The most common early symptom is difficulty in remembering recent events. As ...

. The AI node of the salience network has been observed to be hyperactive in anxiety disorders, which is thought to reflect predictions of aversive bodily states leading to worrisome thoughts and anxious behaviors. In schizophrenia, both structural and functional abnormalities have been observed, thought to reflect excessive salience being ascribed to internally generated stimuli. In individuals with autism, the relative salience of social stimuli, such as face, eyes, and gaze, may be diminished, leading to poor social skills.

Nomenclature

The cingulo-opercular network (CO) has generally been equated with the salience network, but it may represent a distinct but adjacent network or a part of the SN. The CO may involve more dorsal areas, while the SN involves more ventral and rostral areas of the anterior insula and medial frontal cortex containing von Economo neurons. The CO is sometimes also referred to as the cingulo-insular network. The ventral attention network (VAN), also known as the ventral frontoparietal network (VFN) or ventral attention system (VAS), has also been equated with the SN. The VAN is commonly defined as a right-hemisphere-dominant network involving the

and the ventral

frontal cortex The frontal lobe is the largest of the four major lobes of the brain in mammals, and is located at the front of each cerebral hemisphere (in front of the parietal lobe and the temporal lobe). It is parted from the parietal lobe by a groove be ...

that responds to unexpected salient stimuli. Some have defined it as a larger, bilateral network that is a combination of the SN and CO, while others have described it as a part of the salience network involving the more dorsal anterior insular cortex. In 2019, Uddin et al. proposed that ''midcingulo-insular network'' (''M-CIN'') be used as a standard anatomical name for the network that includes the SN, CO, and VAN.

References

{{Human connectomics Brain Neural circuits

Anatomy

Function

Clinical significance

Nomenclature

See also

References