How The Brain Works: A Constructionist Approach to Mind-Brain Correspondence (Part 3)

article how the brain works

October 17, 2024

Brain Networks Are Always Active And Work Together in a Dynamic and Flexible Manner

The seven intrinsic brain networks, outlined in Part 2, are always active to some degree, but their levels of activity vary depending on the task at hand, the context, and internal or external demands. These networks are highly dynamic and interact flexibly to support a wide range of cognitive, emotional, and sensory functions. Let’s explore how this works in more detail:

1. Dynamic Interaction and Switching

The intrinsic brain networks are always active, but certain networks will dominate while others become less active depending on the current demands. For example, when you're engaged in a cognitively demanding task, such as solving a math problem, the Frontoparietal Network (FPN) becomes more active to support focused attention and working memory. Meanwhile, the Default Network (DN), which is typically associated with mind-wandering and self-referential thinking, becomes less active to avoid distraction. Conversely, when you’re at rest or daydreaming, the DN becomes more active, while the FPN reduces its activity.

These networks can also switch control when needed. The Salience Network, for example, plays a critical role in deciding which network should be activated or deactivated in response to changing internal or external events. If a sudden, important stimulus is detected, the Salience Network will help switch activity toward the Dorsal Attention Network (DAN) or other relevant systems. In addition, the Ventral Attention Network (VAN), plays a key role in detecting unexpected or behaviorally relevant stimuli, particularly when they appear outside the current focus of attention. The VAN works alongside the DAN to support reorienting attention when necessary, ensuring that the brain remains responsive to unexpected changes in the environment.

In the study by Yeo et al. (2011), the ventral attention network (VAN) and the salience network (SN) are identified as separate but related large-scale brain networks, which may have functional overlap. While the SN is responsible for detecting salient stimuli and switching between different networks, the VAN is involved in reorienting attention to unexpected stimuli. Thus, the VAN does not include the SN; they are distinct networks, although they interact and can have overlapping functions in responding to salient events.
The ventral attention network (VAN) is considered an intrinsic brain network because it has a consistent resting-state functional connectivity pattern that can be observed even when a person is not actively engaging in specific tasks. The VAN is part of the default, intrinsic functional architecture of the brain, supporting spontaneous attention shifts.
The salience network (SN), on the other hand, is more dynamic, being activated in response to salient stimuli and switching between other networks such as the default mode network (DMN) and the central executive network (CEN), which makes it less purely intrinsic and more context-dependent.

2. Baseline Activity

All of the intrinsic networks exhibit baseline activity, even when we are at rest or not performing any specific cognitive task. This baseline activity helps maintain a state of readiness to respond to changes in the environment or internal states.

The Default Network maintains a baseline of activity that supports self-referential thought and integrates past experiences, preparing the brain for introspective or social tasks.
The Ventral Attention Network remains vigilant for unexpected stimuli, maintaining a readiness to shift attention as needed.
The Limbic Network (LN) maintains ongoing processing of internal emotional states, which can influence subsequent decision-making and behavior, even when not actively engaged in emotionally significant events.

This baseline activity means that the networks are continuously "scanning" and maintaining various processes, helping the brain stay ready to switch into a more active mode as soon as needed.

3. Parallel Processing

Different brain networks can be active in parallel, supporting multiple types of processing at the same time. For example, you could be engaged in a conversation that involves the Frontoparietal Network for decision-making and the Dorsal Attention Network for focused attention. Simultaneously, you might also be processing bodily sensations, like hunger or fatigue, via the Salience Network. This parallel activity allows the brain to manage different types of information simultaneously, facilitating seamless integration of cognition, perception, and bodily regulation.

Parallel processing allows us to combine multiple functions—such as speaking, interpreting the context of the conversation, and keeping track of emotional cues—all while maintaining awareness of our body. This overlapping activity highlights the brain's incredible ability to integrate information across different domains.

4. Modulation by Context and State

Although all seven networks are always "on" to some degree, context and brain state significantly influence their relative levels of activity:

In focused attention tasks, such as reading or working on a project, the Dorsal Attention Network and Frontoparietal Network become more active, while the Default Network reduces activity to prevent distractions.
During emotionally significant events, the Salience Network becomes more engaged to integrate bodily sensations and contextual cues, allowing the brain to appropriately respond to emotional stimuli.
During self-reflective or introspective tasks, the Default Network becomes more dominant, often interacting with the Frontoparietal Network to conceptualize emotions or process personal experiences.

This modulation means that the relative activity within these networks is in a constant state of flux, depending on ongoing activities, environmental conditions, and personal internal states. The Salience Network plays a central role in determining which network should be more or less active, ensuring that the brain's resources are allocated appropriately for the task at hand.

Summary

The seven intrinsic brain networks are always working, but their levels of activation shift depending on the tasks being performed, the context, and the demands placed on the brain. These networks operate dynamically, often in a coordinated fashion, to adapt to different situations. This dynamic interplay allows the brain to remain flexible, responsive, and capable of handling complex, multifaceted demands.

- Ramon D.
Founder, BrainFrst Inc.

References;
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