{
  "id": 10480106,
  "title": "Psychedelics reduce bottom-up brain activity in the default mode network",
  "url": "https://urgent.news/2026/09/28/psychedelics-reduce-bottom-up-brain-activity-in-the-default-mode",
  "topic": "health",
  "section": "Health & Medicine",
  "published": "2026-09-28T16:00:53.000Z",
  "source": {
    "name": "PsyPost",
    "slug": "psypost",
    "url": "https://www.psypost.org/psychedelics-alter-the-trajectory-of-moving-brain-waves/"
  },
  "original_language": "en",
  "account": "Psychedelic substances such as LSD and psilocybin diminish the flow of bottom-up brain activity into the default mode network, a region linked to self-reflection and introspection. This effect is observed consistently in both humans and mice, providing a biological basis for how these drugs influence cognition. The study, published in the Proceedings of the National Academy of Sciences, highlights the potential of psychedelics in treating mental health disorders like depression and trauma. Researchers aim to understand the specific ways these substances alter brain function to optimize their therapeutic benefits and risks. The default mode network, a cluster of brain areas responsible for introspective thought and mental rigidity, is often dysregulated in various psychiatric conditions, making it a prime target for innovative therapies. Situated at the top of the brain's processing hierarchy, the default mode network receives information from lower-order sensory areas through a process called bottom-up processing. Top-down processing, on the other hand, uses past experiences and expectations to interpret incoming sensory data. When there is an imbalance in the flow of information between these two directions, it can result in psychological distress or perceptual errors. Previous research has often measured brain activity in static regions, neglecting the dynamic, wave-like movement of signals across the brain's surface. By employing optical flow analysis, researchers have been able to track the direction and intensity of brain activity waves across the cortex more accurately. In the first part of the study, researchers conducted functional magnetic resonance imaging (fMRI) scans on 14 human volunteers who had taken MDMA. Comparing the scans taken after MDMA consumption with those taken after a placebo or no drug, the researchers found that MDMA consistently reduced the overall magnitude of brain waves traveling through the default mode network. Additionally, the drug lowered the proportion of signals moving bottom-up into this network. A second study involving six human participants who ingested psilocybin yielded similar findings. Brain scans of these participants were compared to baseline scans and to an active placebo condition involving methylphenidate, a stimulant that mimics the physical arousal of psilocybin without its psychedelic effects. Like with MDMA, psilocybin reduced the overall magnitude of propagating brain waves in the default mode network, although the reduction in bottom-up directionality did not reach statistical significance. The researchers theorize that this weaker effect may be due to psilocybin's prolonged action, which could have artificially altered the baseline scans taken shortly after drug administration. In a third study, 18 human volunteers received an intravenous infusion of LSD, and their brain activity was compared to scans taken after receiving a saline placebo infusion. Consistent with the previous findings, LSD reduced both the magnitude of moving brain waves and the proportion of bottom-up signals entering the default mode network. To ensure these effects were not specific to humans or the imaging technique, the researchers conducted a study on 14 mice. Using widefield calcium imaging, a method that directly records the physical activity of brain cells with high resolution, the mice were given LSD, diazepam, or dexmedetomidine. Similar to the human subjects, mice administered LSD exhibited reduced magnitude and bottom-up flow of brain activity in the default mode network. Diazepam, an anti-anxiety medication, also decreased bottom-up signals but to a lesser extent than LSD. In contrast, dexmedetomidine increased the proportion of bottom-up signals entering the network. These animal results validated the optical flow technique as a reliable method for measuring genuine changes in nerve cell activity rather than artifacts related to blood flow. The researchers further explored whether these alterations in moving brain activity correlated with the subjective experiences reported by the human participants. In the MDMA study, individuals who experienced the most significant reduction in bottom-up processing also reported intense feelings of impaired control and a greater dread of ego dissolution, a fear of losing one's sense of self. This psychological correlation suggests that excessive suppression of bottom-up information flow might trigger the negative experiences sometimes associated with psychedelic use. Bottom-up processing is essential for grounding individuals in their immediate sensory environment. A severe reduction in this grounding input could leave individuals feeling detached or vulnerable to psychological distress.",
  "summary": "By mapping brain activity like a moving weather system, researchers found that psychedelics consistently reduce the upward flow of sensory information into higher-order brain regions, offering new biological clues into how these drugs alter human consciousness.",
  "key_points": [
    "Psychedelics like LSD and psilocybin reduce bottom-up brain activity in default mode network",
    "Study in humans and mice shows psychedelics' potential in treating mental health disorders"
  ],
  "editors_take": null,
  "illustration": null,
  "coverage": {
    "outlets": 1,
    "also_reported_by": []
  },
  "ai_generated": true,
  "disclaimer": "Summaries, key points and the editor’s take are written by software from other outlets’ reporting and may contain errors — always check the linked original."
}