Time-dependent scale-free brain dynamics during naturalistic inputs

Area of Science:

• Neuroscience
• Physics
• Signal Processing

Background:

• Environmental processes, including sensory inputs, often exhibit power-law distributions.
• The brain's scale-free dynamics and their response to naturalistic stimuli, particularly the spectral exponent (β(t)), are not fully understood.
• Investigating how the brain dynamically adapts its spectral exponent to changing inputs is crucial for understanding neural processing.

Purpose of the Study:

• To investigate the dynamic, time-dependent spectral exponent (β(t)) in the brain during naturalistic audiovisual input (movie-watching).
• To examine the relationship between the brain's dynamic spectral exponent (β(t)) and inter-subject correlation (ISC(t)) in early sensory regions.
• To determine how the brain's shift from intrinsic to stimulus-driven scale-free dynamics modulates shared brain activity.

Main Methods:

• Functional magnetic resonance imaging (fMRI) was used to measure brain activity.
• Time-varying inter-subject correlation (ISC(t)) was calculated to assess shared brain activity.
• The time-dependent spectral exponent (β(t)) was analyzed in visual and auditory regions during rest and movie-watching using the 7 Tesla Human Connectome Project dataset.

Main Results:

• The brain's spectral exponent (β(t)) demonstrated distinct temporal structures in sensory regions during naturalistic input compared to rest.
• A positive correlation was found between the time-dependent spectral exponent (β(t)) and inter-subject correlation (ISC(t)) during movie-watching.
• Subject groups, differentiated by the change in β(t) from rest to movie-watching, showed varying β(t)-ISC(t) correlations, indicating modulation of shared brain activity by scale-free dynamics.

Conclusions:

• The brain exhibits dynamic, time-dependent scale-free dynamics during naturalistic audiovisual input.
• There is a positive relationship between the brain's time-dependent spectral exponent (β(t)) and inter-subject correlation (ISC(t)), suggesting higher exponents correlate with greater shared brain activity.
• The brain's adaptation of its scale-free dynamics in response to stimuli influences the degree to which sensory inputs are imprinted on neural activity.