Context-Dependent Changes in Degree-Power Coupling of the Default Mode Network Under Psilocybin
Poster No:
1965
Submission Type:
Abstract Submission
Authors:
Matthew Greaves1, Leonardo Novelli2, Devon Stoliker3, Adeel Razi4
Institutions:
1Monash University, Clayton, Victoria, 2Monash University, Melbourne, Victoria, 3Melbourne University, Melbourne, Victoria, 4Monash University, Melbourne, VIC
First Author:
Co-Author(s):
Introduction:
Psilocybin reduces the low-frequency power of neuronal fluctuations and the coupling between structural and functional connectivity, particularly within the default mode network (DMN; Siegel et al., 2024). Thus, understanding psilocybin-induced altered states of consciousness requires models that explain how these changes in power and coupling alter the brain's directed connectivity dynamics. Recently, we introduced a structural-spectral dynamic causal model (DCM) that leverages structural connectivity to constrain the power spectra of endogenous neuronal fluctuations (Greaves et al., 2024). Here, we apply structural-spectral DCM to investigate psilocybin-induced changes across four naturalistic tasks.
Methods:
We collected diffusion-weighted and multi-echo functional MRI data from 60 healthy, psychedelic-naive adults during baseline and psilocybin sessions. Imaging tasks in both sessions included rest, music-listening, meditation, and movie-watching. Structurally informed effective connectivity was inferred using structural-spectral DCM of the DMN. This model uses the normalized structural connectivity degree of each region to constrain the power spectrum of neuronal activity endogenous to that region (a proxy for inputs from regions outside the DMN). Technically, we assumed a linear relationship between the structural degree of each region and the power-law decay of its endogenous power spectrum.
Results:
We found context-dependent effects of psilocybin on the relationship between structural connectivity and neuronal dynamics within the DMN. Across tasks, the intercept of the degree-to-power-law decay function showed significant increases under psilocybin (relative to baseline), reflecting greater low-frequency power, regardless of the structural degree (Fig. 1a). During rest, the slope (reflecting the influence of structural degree) also increased. In contrast, during meditation and movie-watching under psilocybin, we found a trend toward the decoupling of structural degree and power-law decay (negative slope). Psilocybin also altered effective connectivity during music, meditation, and movie tasks, increasing afferent influences on the right medial prefrontal cortex (Fig. 1b-d).
Conclusions:
Our findings support the DMN's central role in psilocybin-induced brain dynamics. At baseline, structural connectivity influenced power-law decay across all tasks. Under psilocybin, this influence increased during rest but decreased during tasks for which participants were instructed to focus on thoughts (meditation) or attend to any perceived emergent patterns in a cloud video (movie-watching). Interestingly, we observed increased low-frequency power under psilocybin, which differs from previous findings. Psilocybin also modulated effective connectivity during tasks, enhancing afferent input to the right medial prefrontal cortex, consistent with other studies of psychedelics (Stoliker et al., 2023). These results highlight the utility of structural-spectral DCM in understanding psilocybin's effects on brain dynamics and structure-function relationships.
References:
Greaves, M. D., et al. (2024). Structurally informed models of directed brain connectivity. Nature Reviews Neuroscience. https://doi.org/10.1038/s41583-024-00881-3
Siegel, J. S., et al. (2024). Psilocybin desynchronizes the human brain. Nature, 632(8023), 131–138. https://doi.org/10.1038/s41586-024-07624-5
Stoliker, D., et al. (2023). Effective Connectivity of Functionally Anticorrelated Networks Under Lysergic Acid Diethylamide. Biological Psychiatry, 93(3), 224–232. https://doi.org/10.1016/j.biopsych.2022.07.013
References:
Greaves, M. D., et al. (2024). Structurally informed models of directed brain connectivity. Nature Reviews Neuroscience. https://doi.org/10.1038/s41583-024-00881-3
Siegel, J. S., et al. (2024). Psilocybin desynchronizes the human brain. Nature, 632(8023), 131–138. https://doi.org/10.1038/s41586-024-07624-5
Stoliker, D., et al. (2023). Effective Connectivity of Functionally Anticorrelated Networks Under Lysergic Acid Diethylamide. Biological Psychiatry, 93(3), 224–232. https://doi.org/10.1016/j.biopsych.2022.07.013
Modeling and Analysis Methods:
Bayesian Modeling
Diffusion MRI Modeling and Analysis
fMRI Connectivity and Network Modeling 2
Novel Imaging Acquisition Methods:
Multi-Modal Imaging 1
Keywords:
Computational Neuroscience
FUNCTIONAL MRI
MRI
Tractography
Other - Psychedelics
1|2Indicates the priority used for review
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Fischl, B. (2012). FreeSurfer. NeuroImage, 62(2), 774–781. https://doi.org/10.1016/j.neuroimage.2012.01.021
Smith, S.M. (2004). Overview of FSL. NeuroImage, 23(S1), S208–S219. https://doi.org/10.1016/j.neuroimage.2004.07.051