Psychedelics Align Brain Activity With Context

Inspired by Devon Stoliker, Moein Khajehnejad, Mana Biabani et al.

Psychedelics can profoundly alter consciousness by reorganizing brain connectivity, producing acute experiences that shape lasting psychological change [1,2]. Psychedelic dynamics are commonly described as desynchronized or entropically disordered, yet how the brain organizes during commonly reported experiences of self- and boundary-dissolution – and how context shapes this organization – remains unclear [3].

How does psilocybin reshape brain connectivity and the sense of self, and what role does context play in shaping these changes and the resulting subjective experiences?

To explore these questions, Stoliker and colleagues conducted the largest single-site psychedelic neuroimaging study to date. The research investigated the reorganization of brain connectivity, context-dependent brain dynamics, and their relationship to subjective experiences such as self-dissolution and feelings of interconnectedness.

Specifically, the team examined how sensory context influences communication between the hippocampus and the Default Mode Network (DMN), as well as changes in neural oscillations and signal complexity measured via EEG.

The study involved 62 healthy adults aged 18–55 with no previous meaningful psychedelic experience. Participants received a single 19 mg oral dose of psilocybin and underwent fMRI and EEG recordings across four conditions: rest, guided meditation, music listening, and movie viewing. Brain activity was compared directly between baseline (without psilocybin) and psilocybin sessions.

Together, the findings reveal how psilocybin alters the balance between internal and external processing, allowing brain activity to become more aligned with context and potentially contributing to meaningful psychological changes [7].

Neural Mechanisms and the Sense of Self

Psychedelics can profoundly change how people experience their inner feelings and the outside world, often leading to experiences described as among the most meaningful in their lives. Research suggests that these experiences may have lasting therapeutic benefits, including reduced depression, anxiety, and addiction-related symptoms, as well as increased social connectedness and overall well-being [4].

The brain constructs perception and the sense of self by integrating external sensory information with internal models through structural and functional connections between sensory and associative regions [5,6].

Classical psychedelics act on serotonin 5-HT2A receptors, promoting structural and functional plasticity – including dendritic spine formation in the medial prefrontal cortex – which is linked to lasting behavioral changes. These effects reshape large-scale brain connectivity and reorganize communication between associative networks, intensifying feelings of immersion where the boundaries between space, time, and self become less distinct and more interconnected [8,9,10].

The Default Mode Network (DMN) serves as the central mediator supporting the integration of information from diverse associative regions spanning spatial, temporal, and self-referential contexts [11]. Under psilocybin, connectivity patterns that constrain networks relax, permitting novel interactions between sensory and associative regions to emerge [12] and altering the connectivity underlying emotion, cognition, and perception [13].

Reorganization of Brain Connectivity Under Set and Setting

Psychedelic effects are highly context-sensitive, strongly influenced by mindset (set) and environment (setting) – factors widely recognized in clinical guidelines [14]. Understanding how context shapes therapeutic change requires examining how psychedelics alter functional brain integration and connectivity across different sensory inputs.

The study shows that psilocybin increases global functional connectivity in associative brain regions while reducing it in sensory areas during eyes-closed conditions (rest, meditation, and music). However, during eyes-open movie viewing, connectivity increases in both regions, highlighting the fundamental influence of sensory context. Furthermore, fMRI and EEG findings reveal that eyes-closed brain activity becomes more similar to eyes-open activity. Machine learning analyses also uncovered structured, context-aligned patterns of brain activity that conventional time-averaged analyses failed to detect.

Dynamic causal modeling (DCM) further revealed that psilocybin alters effective connectivity between the anterior hippocampus (aHip) and core DMN regions depending on context. These changes were modest during eyes-closed conditions but strongest during eyes-open movie viewing, demonstrating that sensory context directly directs the reorganization of hippocampus–DMN communication.

Subjective Experience and Interconnectedness

Machine learning analyses revealed that stronger context-aligned brain activity was particularly associated with positively experienced self-dissolution and boundary-dissolution, whereas associations with anxiety and cognitive impairment were weak or negative. Participants reporting more intense mystical experiences also exhibited stronger context-specific neural organization. These findings directly link context-dependent brain dynamics to the subjective experience of interconnectedness, described by the researchers as embeddedness.

Neural Oscillations, Signal Complexity, and Sensory Filtering

EEG analyses revealed that psilocybin alters neural oscillations and signal complexity depending on sensory context. During eyes-closed conditions, psilocybin reduced theta, alpha, and, to a lesser extent, beta power, while modestly increasing gamma activity, particularly in frontal regions. These changes were less pronounced during eyes-open movie viewing, suggesting reduced disruption of neural activity during externally directed attention.

Crucially, psilocybin increased signal complexity during eyes-closed conditions and reduced the difference in alpha power between eyes-open and eyes-closed states by 48%. Normally, alpha activity (8–12 Hz) increases when the eyes are closed to filter out external visual noise and regulate internal processing, while dropping when the eyes are open to process external visual input. By suppressing eyes-closed alpha power, psilocybin weakens this gating mechanism. This directly bridges the study’s central theme: psilocybin blurs the distinction between internally and externally directed processing, allowing external sensory context to flood and align with internal brain dynamics.

The Role of Music in Brain Reorganization

Music played a vital role in the study as a contextual element influencing psychedelic experiences. Under psilocybin, participants reported that music felt significantly more emotionally resonant and engaging, with ratings increasing by 16% during fMRI and 21% during EEG sessions. A separate assessment showed a 25% increase in emotional and aesthetic responses to music. Additionally, brain activity showed its greatest global network organization during music listening, highlighting how sensory context shapes both neural dynamics and subjective experiences under psilocybin.

Future Directions

This study opens new perspectives on how psychedelics interact with the brain, the surrounding environment, and subjective experience. Rather than viewing psychedelic effects as purely pharmacological, it invites further exploration of how sensory context, emotional experiences, and neural dynamics interact to shape altered states of consciousness. These findings raise important questions about the role of set and setting, and how a deeper understanding of context-dependent brain activity might inform future psychedelic research and therapeutic approaches.

References

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