Beyond noise to function: reframing the global brain activity and its dynamic topography.

Area of Science:

• Neuroscience
• Complex Systems Analysis
• Cognitive Science

Background:

• The interaction between global and local activity is fundamental in complex systems.
• In the brain, global activity, particularly the global signal in fMRI, has been largely considered non-neuronal noise.
• Understanding the brain's global signal is key to comprehending its functional organization and behavioral modulation.

Purpose of the Study:

• To review findings on the neural basis and functions of the global signal in both healthy and clinical populations.
• To challenge the prevailing view of the global signal as mere noise.
• To propose a new model for understanding global signal's role in brain function and behavior.

Main Methods:

• Review of existing literature and findings from studies on healthy and clinical populations.
• Analysis of functional magnetic resonance imaging (fMRI) data.
• Postulation of a theoretical Dual-Layer Model.

Main Results:

• The global signal is closely coupled with physiological signals, modulating arousal levels.
• It organizes complex dynamic topographies and coordinates various cognitive functions.
• Evidence supports a neural basis for the global signal, extending beyond non-neuronal noise.

Conclusions:

• The global signal plays a significant role in brain function, influencing arousal and cognition.
• A Dual-Layer Model, encompassing background and surface layers, provides a more accurate framework for understanding the global signal.
• Future research should move beyond viewing the global signal as noise and embrace its functional significance.