LSD-induced increase of Ising temperature and algorithmic complexity of brain dynamics

Area of Science:

• Computational Neuroscience
• Neuroimaging
• Complex Systems

Background:

• The brain's self-organization and global dynamics are key areas in computational neuroscience.
• The brain operating near criticality is a supported theory, modeled by Ising models.
• Previous research suggests brain states can be modeled by Ising models at varying distances from criticality.

Purpose of the Study:

• To characterize two brain states (psychedelics-induced vs. placebo) using fMRI data.
• To investigate the entropic brain hypothesis by examining Ising model features and algorithmic complexity.
• To test if psychedelics (LSD) induce a more disordered brain state with higher complexity and Ising temperature.

Main Methods:

• Analysis of resting-state blood-oxygen-level-dependent (BOLD) fMRI data from 15 subjects (placebo and LSD conditions).
• Application of pairwise maximum entropy Ising models to characterize brain states and connectivity.
• Estimation of Lempel-Ziv-Welch (LZW) and Block Decomposition Method (BDM) algorithmic complexity.

Main Results:

• Ising model archetypes showed strong correlation with structural connectome templates.
• LSD condition exhibited lower Ising connectivity, particularly in homotopic (interhemispheric) links, compared to placebo.
• Individualized Ising temperatures were significantly higher in the LSD condition, indicating a shift towards a more disordered state.
• BDM complexity correlated significantly with Ising temperature and condition, suggesting increased complexity under LSD.

Conclusions:

• LSD increases brain dynamics complexity by reducing interhemispheric connectivity, especially homotopic links.
• The brain state under placebo is already above the critical point; LSD shifts it further into a disordered state.
• Findings support the entropic brain hypothesis and the utility of Ising models for characterizing brain states.