Hypothesis

Psilocybin‑induced alterations in cortical excitability and neurotransmitter tone enhance glymphatic clearance during subsequent sleep, thereby promoting selective removal of maladaptive synaptic connections within the default mode network (DMN) and stabilizing antidepressant‑related network reorganization.

Mechanistic Rationale

• Psilocybin’s active metabolite psilocin is a potent 5‑HT₂A agonist that acutely increases neuronal firing and cortical glutamate release. This surge triggers a homeostatic rebound characterized by heightened slow‑wave activity (SWA) during ensuing NREM sleep, a state known to suppress locus coeruleus norepinephrine release. Reduced norepinephrine expands the extracellular interstitial volume from ~15% to >20%, markedly increasing convective glymphatic flow (source).

• Beyond acute receptor effects, psilocybin upregulates brain‑derived neurotrophic factor (BDNF) and TrkB signaling, which in astrocytes upregulates aquaporin‑4 (AQP4) polarization, a key determinant of glymphatic efficiency (source).

• The psilocybin‑driven decrease in DMN functional connectivity and concomitant increase in between‑network integration (frontoparietal, salience) creates a transient “labile” synaptic landscape. During high‑glymphatic flow periods, extracellular metabolites such as amyloid‑β, phosphorylated tau, and activity‑dependent tagging molecules (e.g., Arc, PSD‑95 fragments) are cleared more efficiently. Synapses that exhibit persistent hyper‑connectivity or maladaptive tagging are preferentially removed, whereas adaptive connections reinforced by coincident neuronal activity survive.

• Consequently, the network configuration observed days to weeks after dosing reflects a sleep‑edited connectome: the DMN is less rigid, global integration is heightened, and these changes correlate with clinical remission.

Testable Predictions

1. Sleep Architecture: In healthy volunteers or depressed patients, a single oral dose of psilocybin (25 mg) will increase proportion of N3 (slow‑wave) sleep and SWA power during the first two nocturnal sleep episodes compared with placebo (source).

2. Glymphatic Flux: Using intranasal gadobutrol‑based MRI tracer kinetics, the clearance rate from the cortical subarachnoid space to venous circulation will be significantly higher in the psilocybin condition during sleep, correlating with individual SWA magnitude.

3. DMN Connectivity: Resting‑state fMRI acquired 24 h, 72 h, and 1 week post‑dose will show greater reductions in DMN intra‑connectivity and larger increases in DMN‑frontoparietal coupling in participants who exhibit the greatest glymphatic enhancement.

4. Clinical Correlation: The magnitude of glymphatic enhancement will mediate the relationship between psilocybin‑induced SWA increase and antidepressant response at week 5 (measured by MADRS reduction ≥50%). Mediation analysis should reveal a significant indirect effect.

5. Pharmacological Blockade: Pretreatment with a selective 5‑HT₂A antagonist (e.g., ketanserin) will abolish both the SWA boost and glymphatic increase, confirming receptor dependence.

Falsifiability

If psilocybin fails to augment slow‑wave sleep or glymphatic tracer clearance, or if enhanced clearance does not predict DMN remodeling or clinical outcome, the core claim—that sleep‑dependent glymphatic editing underlies the enduring antidepressant effects of psilocybin—would be refuted.

Broader Implications

Positive results would position sleep not merely as a passive recovery state but as an active collaborator with psychedelic‑induced neuroplasticity, suggesting that optimizing post‑dose sleep (e.g., protecting SWA, avoiding antidepressants that suppress SWA) could amplify therapeutic durability. Conversely, null findings would steer research toward alternative consolidation mechanisms such as protein‑synthesis‑dependent synaptic tagging independent of glymphatic flow.