Salience Network of the Human Brain

Lucina Q. Uddin

• Publisher: Academic Press
• Year: 2016
• ISBN:
  9780128045947
• Topic: Biological Sciences
• Subtopic: Neuroscience
• Index: Biological Sciences

Salience Network of the Human Brain focuses on the multiple sources of stimuli that compete for our attention, providing interesting discussions on how the relative salience—importance or prominence—of each of these inputs determines which ones we choose to focus on for more in-depth processing.

The salience network is a collection of regions of the brain that select which stimuli are deserving of our attention. The network has key nodes in the insular cortex and is critical for detecting behaviorally relevant stimuli and for coordinating the brain's neural resources in response to these stimuli. The insular cortex is a complex and multipurpose structure that plays a role in numerous cognitive functions related to perception, emotion, and interpersonal experience—and the failure of this network to function properly can lead to numerous neuropsychiatric disorders, including autism spectrum disorder, psychosis, and dementia.

• Presents the only publication available that summarizes our understanding of the salience network in one resource
• Authored by a leading research on this important aspect of attention
• Focuses on the multiple sources of stimuli that compete for our attention, providing interesting discussions on how the relative salience—importance or prominence—of each of these inputs determines which ones we choose to focus on for more in-depth processing

Chapter 1

What Is Salience?

Abstract

Salience is a term used to describe the quality of being noticeable, or standing out. Salience is often defined in terms of low-level sensory features (e.g., stimulus color or intensity), but can also be used to describe more high-level cognitive and affective processes (e.g., emotional salience or personal relevance). In either scenario, things that are considered salient are described as such because they attract attention and are meaningful or behaviorally relevant. Salience detection has been studied most thoroughly in the domain of visual search. This chapter provides an introduction to basic definitions of salience as commonly applied in the areas of psychological and neuroscientific research.

Keywords

Attention; visual search; pop out; saliency map

At any given moment, our senses are bombarded with information from a variety of sources. We know that flashing lights and sirens signal emergencies, that the presence of dangerous predators can keep us vigilant, and emotional memories might arise at the slightest provocation. Our brains must continuously parse this abundance of information to allow us to successfully navigate the environment. In order to do this, our nervous system must somehow determine what is critical to direct attention to, and what can safely be ignored. Things that are more salient naturally attract more attention. But what exactly do we mean by “salience”?

When we use the term “salience” in daily life, we often mean to convey the Merriam-Webster dictionary definition of the term: “the quality or state of being salient,” where salient is “very important or noticeable.” Objects, ideas, or events that are “very important or noticeable” have a privileged status in that they attract significant attention and can occupy a disproportionate amount of space in our imaginations. The term salience has been used in multiple domains of psychology and neuroscience to convey this concept of importance and noticeability.

In perception research, and specifically in studies of the visual system, the term salience is typically used to describe aspects of an item that make it stand out relative to its neighbors. For example, the well-known “pop out” effect during visual search (Treisman, 1998) describes the phenomenon that it is easier to identify a target that differs from distractors on one feature than on several features. Certain stimuli are salient by virtue of ease of discrimination from the surroundings (Fig. 1). This type of automatic and effortless salience detection enables rapid direction of visual attention.

Figure 1 Salience in visual search.
Some stimuli are salient by virtue of the “pop out” effect (Treisman, 1998). It is easier to identify a target that differs from distractors on one feature (e.g., color) than on several features. Certain stimuli—the red T, the green bar, and the pink circle—are salient by virtue of ease of discrimination from their surroundings.

The concept of a “saliency map” (Koch & Ullman, 1985), derived from empirical work in visual search, is the idea that a two-dimensional map encodes the saliency of objects in the visual environment. Computational models of this process are based on the idea that early visual features such as color and intensity are computed based on retinal input and activity from these feature maps is combined at each location, giving rise to a topographic saliency map. The “winner-take-all” system subsequently detects the most salient location and directs attention toward it (Itti & Koch, 2000). This type of model is limited to the bottom-up, stimulus-driven control of attention. However, contextual factors and previous experience can also contribute to perceptions of what is salient.

Most theories of salience detection and attention adopt a two-component framework incorporating both bottom-up processes such as the ones just described, as well as top-down contextual influences (Itti & Koch, 2001). In an influential model of attention, Corbetta and colleagues describe two partially segregated networks: a ventral-attention network responding to external environmental stimuli, and a dorsal-attention network responsible for goal-directed, top-down processing (Corbetta & Shulman, 2002). Chapters 2 and 3, Anatomy of the Salience Network and Functions of the Salience Network, will further elaborate on the anatomy and function of these networks as they relate to salience processing.

In areas outside of vision research and computational modeling of attention, salience is often described using a different emphasis, namely that of personal relevance. In such cases, stimuli and/or events that are meaningful or emotionally provocative are termed as salient. This conceptualization of salience as a relatively high-level cognitive process can be seen, e.g., in the literature on emotional learning (Dunsmoor, Murty, Davachi, & Phelps, 2015). In the area of memory research, saliency is thought to influence the likelihood that an event or object will be remembered; objects can be salient because of their meaning or semantic relationship with other objects. Some have proposed that perceptual- (based on low-level sensory features) and semantics-related (based on prior knowledge) salience affect encoding and memory representation in different ways, acting through dorsal and ventral neural systems, respectively (Santangelo, 2015).

In the addiction literature, the term incentive salience or motivational salience refers to the “wanting” that accompanies most addictions, and is thought to be modulated by dopamine (Tibboel, De Houwer, & Van Bockstaele, 2015). As with the definitions of salience we have discussed, the term salience again highlights the property of standing out or being attention-grabbing, in this case to the point of pathology.

As we will review throughout the next several chapters, the concept of salience is ubiquitous in psychology and neuroscience; thus a great deal of research has been devoted to understanding the mechanisms by which salience detection occurs in the brain and the anatomical structures that support it.

References

1. Corbetta M, Shulman GL. Control of goal-directed and stimulus-driven attention in the brain. Nature Reviews Neuroscience. 2002;3(3):201–215.

2. Dunsmoor JE, Murty VP, Davachi L, Phelps EA. Emotional learning selectively and retroactively strengthens memories for related events. Nature. 2015;520(7547):345–348.

3. Itti L, Koch C. A saliency-based search mechanism for overt and covert shifts of visual attention. Vision Research. 2000;40(10–12):1489–1506.

4. Itti L, Koch C. Computational modelling of visual attention. Nature Reviews Neuroscience. 2001;2(3):194–203.

5. Koch C, Ullman S. Shifts in selective visual attention: Towards the underlying neural circuitry. Human Neurobiology. 1985;4(4):219–227.

6. Santangelo V. Forced to remember: When memory is biased by salient information. Behavioural Brain Research. 2015;283:1–10.

7. Tibboel H, De Houwer J, Van Bockstaele B. Implicit measures of “wanting” and “liking” in humans. Neuroscience and Biobehavioral Reviews. 2015;57:350–364.

8. Treisman A. Feature binding, attention and object perception. Philosophical Transactions of the Royal Society of London Series B, Biological Sciences. 1998;353(1373):1295–1306.

Chapter 2

Anatomy of the Salience Network

Abstract

A set of brainstem, subcortical, and cortical structures form what has come to be known as the “salience network.” Ascending inputs from visceroautonomic sensors communicate information about the body to the frontoinsular cortex (FIC). Interoceptive signals enter through the dorsal posterior insula to reach the FIC. Cortical nodes of the salience network include the FIC and anterior cingulate cortex, which together integrate these ascending signals to coordinate other large-scale cortical networks and trigger visceromotor responses to salient stimuli. Affiliated networks including the ventral attention and cinguloopercular networks may anatomically overlap the salience network at specific nodes.

Keywords

Insula; anterior cingulate; connectivity; limbic system

The view that the brain functions as a vast, interconnected network currently dominates the cognitive neuroscience landscape (Pesso...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Dedication
• List of Figures
• Acknowledgment
• Chapter 1. What Is Salience?
• Chapter 2. Anatomy of the Salience Network
• Chapter 3. Functions of the Salience Network
• Chapter 4. Salience Network Across the Life Span
• Chapter 5. Salience Network Dysfunction
• Chapter 6. Future Directions in Salience Network Research
• Index