Scientists have often wondered how the brain can take in new experiences without erasing stored memories. However, a new study in Nature now identifies a circuit-level mechanism that may help answer this question—and it may also offer clues for improving artificial intelligence.

Researchers at NYU Langone Health recorded the activity of hundreds of neurons simultaneously across several brain regions in mice. By tracking how signals move from the hippocampus to the neocortex, where long-term memories are kept, they found that a subset of hippocampal neurons appears to participate in routing information between regions in distinct patterns. These cells participate in both incoming and outgoing signaling, but do so using distinct patterns of activity.

Separate Channels Through the Same Cells

The study focused on a series of interconnected brain regions: CA3, which processes rapidly changing information; CA1, which serves as a central hub; and the retrosplenial cortex, which is important for navigation and spatial memory. About one in four CA1 neurons receives most of the signals from CA3. When these same neurons send signals to the retrosplenial cortex, they fire in a different pattern, creating a separate outgoing channel using the same cells.

Rather than using new neurons, the brain separates these channels by changing how the same neurons fire together. The researchers suggest this arrangement may help reduce interference between new learning and more stable cortical memories.

“Our findings help explain how memory can be both moldable and enduring,” said co-lead author Joaquín Gonzalez, PhD, a postdoctoral fellow in the Department of Psychiatry at NYU Grossman School of Medicine. “By changing how the same cells fire together instead of turning on new cells, the brain can keep information organized and protect older memories.”

What Happens During Sleep

The CA1 neurons involved in learning during the day also stay active at night. The researchers found that these cells remain busy during sleep events called sharp-wave ripples, which are bursts of activity the hippocampus uses to replay and strengthen memories from the day.

Since overlapping neurons are recruited during both waking activity and sleep replay, the same circuit elements appear to participate in both learning and consolidation. This theoretically allows the brain to use a single system for both learning and storing memories, without the two processes interfering with each other.

“Our study shows how learning and memory consolidation can coexist in the same network,” said co-lead author Mihály Vöröslakos, MD, PhD. “Our discovery was made possible because for the first time, we were able to record hundreds of individual neurons across all the key regions simultaneously in animals that were moving around naturally.”

Implications for Disease and AI

The system identified in this research may help explain how memory disorders begin. In Alzheimer’s disease, for example, the hippocampal circuits examined here are some of the earliest to deteriorate. These networks are essential for sorting and organizing new experiences.

“Our discovery of a ‘memory switchboard’ deep in the hippocampus may provide clues as to how memory circuits fail in Alzheimer’s disease,” said co-senior author Zhe S. Chen, PhD, a professor in the Departments of Psychiatry and Neuroscience at NYU Grossman School of Medicine.

Artificial intelligence systems have a hard time holding onto what they’ve already learned when faced with new tasks, a problem researchers call catastrophic forgetting. The human brain appears able to update memories without catastrophic forgetting by altering the use of existing neural circuits. By studying how our brains pull this off, scientists hope to design AI that can keep learning new things without forgetting the old.

“By showing how the mammalian brain can safeguard memories during learning, our research may offer a biological blueprint for designing next-generation AI technology that can update itself continuously without overwriting what it has already acquired,” said co-senior author György Buzsáki, MD, PhD, the Biggs Professor of Neuroscience at NYU Grossman School of Medicine.

The researchers plan to investigate whether similar switchboard-like channels exist in other memory circuits. The authors caution that their findings in mice under controlled conditions do not yet allow conclusions about the human brain.

Austin Burgess is a writer and researcher with a background in sales, marketing, and data analytics. He holds an MBA, a Bachelor of Science in Business Administration, and a data analytics certification. His work focuses on breaking scientific developments, with an emphasis on emerging biology, cognitive neuroscience, and archaeological discoveries.

For five years, an elderly woman with advanced Alzheimer’s disease had spoken mostly in single words, needed help walking, and showed little spontaneous interaction with the people around her. Then, roughly 19 hours after receiving a high dose of psilocybin-containing mushrooms, she emerged from a prolonged, deep sleep-like state and began talking about her life.

The striking episode, described in a new case report published in Frontiers in Neuroscience, does not show that psilocybin reverses Alzheimer’s disease. The researchers are careful to stress that this was a single patient, observed in a real-world private clinical setting without brain imaging, formal sleep monitoring, or standardized cognitive testing.

Still, the study’s authors say the case raises the interesting possibility that in late-stage dementia, some functional abilities may indeed remain dormant rather than be completely lost.

“Advanced Alzheimer’s disease is generally regarded as a stage of irreversible functional decline,” researchers write. “This case documents transient multidomain functional improvement in advanced Alzheimer’s disease following psilocybin administration.”

The case involved a Japanese-American woman in her 80s with a 10-year history of Alzheimer’s disease. The patient was described as being in an advanced stage of dementia, with the previous five years being noted for severe decline.

Her speech had become mostly monosyllabic, and she had chronic urinary incontinence, executive dysfunction, dysphagia, dependent mobility, flat affect, prolonged somnolence, and a severe reduction in spontaneous communication.

Her diagnosis had been made clinically about a decade earlier, based on a steadily progressive neurodegenerative course, memory impairment, language reduction, executive dysfunction, and functional decline.

The intervention was a single oral dose of 5 grams of psilocybin-containing mushrooms from the “Enigma” strain. Researchers note that no established psilocybin dosing framework exists for advanced dementia, and the dose was high by almost any comparison.

Recreational users commonly describe 1 to 3 grams of dried Psilocybe cubensis mushrooms as a typical range, while doses around 3.5 grams or more are generally considered strong. A 5-gram dose is often treated as an especially intense experience. However, direct comparisons are imprecise because psilocybin content can vary widely between mushroom species, strains, batches, and even different parts of the same mushroom.

The study also notes that the dose was “relatively high compared with dosing approaches commonly used in modern clinical trials,” which typically use carefully measured amounts of purified psilocybin rather than whole mushrooms.

One month later, after some improvements persisted, the patient underwent a second supervised session using 3 grams.

The first session produced a dramatic acute response. The patient experienced autonomic activation, profuse sweating, suspected hyperthermia, and what the researchers describe as a prolonged deep sleep-like state. Exact temperature measurements were not available.

The study’s timeline shows that the first 12 hours were dominated by autonomic and sleep-like effects. At about 19 hours, the patient spontaneously awakened and produced roughly four hours of autobiographical speech.

By the first day, she showed increased alertness and recognition of family. By the second day, she was independently walking. By days two and three, she was dressing herself and showing spontaneous initiative. Around the same time, her diapers remained dry, including at night.

The improvement in continence was particularly notable to researchers because urinary control depends on more than a single simple reflex. It requires awareness of bodily signals, executive inhibition, and coordination among brain networks affected by dementia. The report states that the patient remained continent one month after the initial session, which was one reason a second session was performed.

During that second session, the patient reportedly remained more verbally expressive and described positive imagery involving surfing with her son on a peaceful island.

Researchers also observed improved facial expressivity, emotional reciprocity, spontaneous humor, and greater agility while walking. At one point during follow-up, the patient spontaneously said, “It is pleasant to come here.”

The study’s broader importance is in what it may suggest about the brain in advanced neurodegenerative disease. Alzheimer’s is usually understood as a progressive condition in which neurons and networks progressively deteriorate, stripping away memory, communication, mobility, and autonomy. By the advanced stage, treatment is largely supportive, and meaningful functional recovery is generally considered unlikely.

Psilocybin, however, is known to transiently alter large-scale brain dynamics via activation of the serotonin 5-HT2A receptor. Researchers point to prior human neuroimaging studies showing changes in default mode network integrity, network segregation, and functional connectivity after psilocybin administration. They also cited preclinical research suggesting psychedelics may promote structural and functional plasticity, including dendritic growth and synaptic remodeling.

That does not mean psilocybin repaired the patient’s Alzheimer’s disease. Instead, researchers suggest a more measured interpretation. The drug may have temporarily altered brain network activity, allowing remaining functional systems to reintegrate or become accessible again, at least for a limited period.

The report does not claim that plaques, tangles, or neurodegeneration were reversed. It also does not show that other patients would experience similar results. Because this was a single case, there was no control group, no placebo comparison, no formal biomarker confirmation, and no standardized cognitive testing to measure the degree of change.

Researchers acknowledge that mixed or alternative neurodegenerative contributions, including vascular components, cannot be fully excluded. Although they found no evidence of acute delirium, intoxication, or another acute neurological diagnosis during the observation period, the case remains observational. Causality cannot be established, and fluctuations in neurodegenerative disease cannot be completely ruled out.

The safety picture is also incomplete. While no severe persistent adverse effects, prolonged agitation, clinically significant cardiovascular instability, persistent psychotic symptoms, delayed neurological deterioration, or delayed medical complications were observed during follow-up, the acute phase included suspected hyperthermia and profuse sweating. In frail elderly patients, especially those with advanced dementia, such responses could carry serious risks.

For that reason, the findings should not be read as a green light for unsupervised psychedelic use in dementia patients. Psilocybin is still a powerful psychoactive compound, and older adults with complex neurological disease may be especially vulnerable to complications.

Ultimately, the value of the report doesn’t lie in providing a treatment recommendation but in documenting an unusual clinical observation that researchers say warrants controlled investigation.

The case also lands amid a flood of scientific interest in psychedelics as tools for studying brain plasticity, perception, memory, and large-scale network dysfunction.

As The Debrief has previously reported, recent brain-imaging work has found that psilocybin can temporarily dissolve familiar brain-network patterns tied to the sense of self, while other studies suggest psychedelics may redirect visual processing toward memory-related regions. Additional research has analyzed how a single dose of psilocybin may produce lasting brain changes, how the compound can reshape neural pathways associated with depression, and how psychedelic effects may be influenced by factors such as exercise, food restriction, and immune signaling.

However, most clinical work with psilocybin has centered on psychiatric conditions such as depression, anxiety, PTSD, and substance use disorders.

More recently, researchers have begun asking whether similar neuromodulatory effects might have relevance for people with mild cognitive impairment or early Alzheimer’s disease.

Published clinical data involving advanced dementia remain extremely limited, which is why the new report is best understood not as evidence of a treatment, but as a provocative case study that may help guide future controlled research.

This recent case does not prove efficacy, but it questions assumptions about what may remain possible in a brain already deeply affected by Alzheimer’s disease.

If future studies find similar effects under supervised conditions, the implications could be significant, not only for dementia care but also regarding understanding how much latent function can persist beneath the outward appearance of severe decline.

“Residual functional capacity may persist in advanced Alzheimer’s disease and may become transiently accessible following psilocybin induced modulation of large-scale brain networks,” researchers conclude. “Systematic investigation is warranted.”

Tim McMillan is a retired law enforcement executive, investigative reporter and co-founder of The Debrief. His writing typically focuses on defense, national security, the Intelligence Community and topics related to psychology. You can follow Tim on Twitter: @LtTimMcMillan.  Tim can be reached by email: tim@thedebrief.org or through encrypted email: LtTimMcMillan@protonmail.com