The salience network (SN) is one of the brain’s major intrinsic connectivity networks, functioning as a system that continuously monitors both the external world and the body’s internal state. It acts as a filter, determining which information is relevant enough to demand the brain’s attention and resources. The fundamental purpose of this network is to detect “salient” stimuli, which are events or signals that are subjectively important, novel, or emotionally significant at a given moment. This filtering mechanism is fundamental to all cognitive processes, allowing for effective decision-making and appropriate behavioral responses to a dynamic environment.
Core Components and Function
The salience network is primarily anchored by two cortical hubs: the anterior insula (AI) and the dorsal anterior cingulate cortex (dACC). These two regions are strongly connected by white matter tracts, notably along the uncinate fasciculus, forming a tightly coupled functional unit. The anterior insula integrates sensory information from the outside world with the body’s internal state, known as interoception. Interoceptive signals, such as heart rate, blood pressure, or pain, enter the insula, which then processes them to create a sense of the body’s current condition. The anterior cingulate cortex component is then thought to use this integrated information to help guide action and maintain control signals to other attention networks. The term “salience” in this neurological context refers to any stimulus—internal or external—that is homeostatically, emotionally, or cognitively important enough to warrant a response.
Subcortical Nodes
Beyond the main cortical hubs, the network includes subcortical nodes such as the amygdala, hypothalamus, and ventral striatum. These nodes contribute to processing emotional and motivational aspects of salience. The SN provides a continuous, moment-to-moment assessment of what matters most for survival and goal-directed behavior by integrating sensory input, emotional information, and internal bodily states.
The Network Switching Mechanism
The most functionally remarkable role of the salience network is its capacity to act as a dynamic switch within the “Triple Network Model” of brain organization. This model describes the dynamic interaction among three large-scale networks: the Salience Network (SN), the Default Mode Network (DMN), and the Central Executive Network (CEN), also known as the Frontoparietal Network (FPN). The DMN is active during internal thought processes, such as daydreaming, self-reflection, planning, and memory retrieval.
The CEN is engaged when the brain is focused on complex, externally directed tasks, such as solving a math problem, paying close attention to a conversation, or engaging in goal-directed behavior. These two networks are typically anticorrelated, meaning that when one is highly active, the other is suppressed. This relationship prevents the brain from being simultaneously lost in thought and focused on an external task. The salience network is the conductor that manages this competitive relationship.
When the salience network detects a highly relevant stimulus, such as a fire alarm or a sudden unexpected touch, it initiates a swift transition in brain states. This mechanism involves the SN, particularly the anterior insula, actively inhibiting the DMN, thereby suppressing internal thought and self-referential processing. Simultaneously, the SN activates the CEN, immediately shifting the brain’s resources to external attention, working memory, and goal-directed action. For example, if a person is deep in thought (DMN active) and a phone rings (salient external stimulus), the SN detects the sound, shuts down the DMN, and activates the CEN to engage the person in answering the phone.
Role in Psychological and Neurological Conditions
Dysfunction within the salience network is implicated in a broad spectrum of psychological and neurological conditions, often by disrupting the balance between internal and external focus. A common thread across these disorders is a failure of the SN to properly assign or modulate the relevance of stimuli, leading to a “misattribution of salience.”
In schizophrenia, for instance, there is evidence of SN hyperactivity, which may cause individuals to assign excessive importance to otherwise irrelevant stimuli. This misattribution can manifest as hallucinations or delusions, where an irrelevant thought or sensory input is perceived as highly significant or threatening.
Conversely, in anxiety and depression, SN dysfunction can lead to an excessive focus on internal, negative thoughts and emotional states, effectively resulting in an overdrive of the DMN. This prolonged engagement with internal negativity, coupled with a heightened sensitivity to potential threats processed by the SN, contributes to the characteristic symptoms of rumination and hypervigilance.
In conditions like Autism Spectrum Disorder (ASD), altered SN function is believed to underlie the hypo- or hyper-sensitivity to sensory input. The network may either fail to filter out overwhelming sensory details (hyper-sensitivity) or fail to flag socially relevant cues (hypo-sensitivity), disrupting the ability to effectively navigate social and sensory environments.