Summary: A new study has identified the world’s first “neural switch” responsible for selectively retrieving recent memories over past ones. The researchers discovered a specific neural circuit connecting the medial septum (MS) and the medial entorhinal cortex (MEC) that actively dictates whether the brain utilizes up-to-date information or reverts to old behavioral patterns.
This breakthrough uncovers how the brain maintains cognitive flexibility and opens radical new therapeutic pathways for treating dementia and Alzheimer’s disease, where patients frequently become “stuck” in past memories.
Key Facts
- The Septo-Entorhinal Circuit: The newly discovered neural switch is a specific pathway connecting the medial septum (the brain’s memory “conductor”) to the medial entorhinal cortex (the gateway to the hippocampus).
- Active Chronological Selection: Memory retrieval is not just a passive replaying of stored traces; the brain features an active regulatory system that evaluates competing memories and deliberately highlights the most recent data.
- The Regression Effect: When researchers artificially blocked this neural circuit using optogenetic light tools, experimental animals became entirely incapable of utilizing recent information, reverting to past behavioral patterns and shifting hippocampal neural activity back to a past state.
- Rhythm-Dependent Retrieval: Effective memory selection relies heavily on maintaining an “online state” characterized by theta waves (active during learning and concentration). Rapidly fluctuating between online and offline states (delta waves) significantly degrades the brain’s ability to pull up recent memories.
Source: KAIST
“Why do patients with dementia or cognitive decline remain stuck in past memories?”
KAIST researchers have identified, for the first time in the world, the existence of a “neural switch” in the brain that selectively retrieves the most recent memories.
This study reveals the principle by which the brain selects necessary information between past memories and new memories, presenting new possibilities for future treatments for memory decline and reduced cognitive flexibility.
KAIST announced on the 17th of May that a research team led by Professor Jin-Hee Han of the Department of Biological Sciences has discovered, for the first time in the world, that a specific neural circuit connecting the medial septum (MS, a brain region that regulates memory and learning) and the medial entorhinal cortex (MEC, a brain region connected to the hippocampus that processes memory information) switches between past and recent memories and plays a key role in selecting up-to-date information appropriate for the situation.
We live by updating our memories through new experiences every day. For example, if the restaurant we visited today was more satisfying than the one we visited yesterday, the brain modifies the existing memory to reflect the new information.
In this way, the ability to select necessary information between past and present memories is central to higher cognitive functions such as decision-making, problem-solving, future prediction, and logical reasoning. However, the principle by which the brain distinguishes and switches between memories has long remained unknown.
The research team focused on the medial septum, located deep within the brain. The medial septum regulates the activity rhythms of the hippocampus and acts as a “conductor” that helps the brain effectively store and retrieve information.
The study found that when specific neurons in the medial septum send signals to the medial entorhinal cortex, a brain region that processes memory information and delivers it to the hippocampus, the brain is better able to recall recent memories.
Conversely, when the research team artificially blocked this neural circuit using light, experimental animals were unable to use recent information and behaved according to past patterns.
Neural activity in the hippocampus, which plays an important role in memory representation, also reverted to a past state. This shows that the circuit acts as a “neural switch” that selects the most recent information needed for the current situation among multiple memories.
The research team also analyzed memory performance according to brain activity states. Our brain repeatedly shifts between an “online state” (theta waves, brain waves activated during learning and concentration), in which it actively processes information, and an “offline state” (delta waves, slow brain waves that appear during sleep or rest), which is a resting state.
The analysis showed that the longer the online state was maintained, the better recent memories were recalled, while frequent switching between online and offline states significantly reduced memory retrieval ability. This suggests that specific brain rhythms and states are important neurobiological indicators that determine effective memory retrieval.
This study is significant in that it identified the mechanism by which the brain flexibly reflects new information while maintaining past memories. The research team expects that this discovery could lead to the development of new therapeutic technologies to improve memory decline and reduced cognitive flexibility in patients with degenerative brain diseases such as dementia and Alzheimer’s disease.
Professor Jin-Hee Han stated, “This study presents a new paradigm for understanding the principle by which our brain organizes and uses numerous experiences in chronological order,” adding, “Previously, memory retrieval was understood simply as the replaying of stored traces, but through this study, we proved that the brain has a regulatory system that actively selects recent information among competing memories.”
Funding: This research was supported by the Mid-Career Research Program (National Research Foundation of Korea), the Samsung Science and Technology Foundation, and the KAIST Jang Young Sil Fellow Program.
Key Question Answered:
A: It has long been a mystery why degenerative brain diseases lock people in the deep past. This study reveals that the issue isn’t necessarily that recent memories are gone; rather, the brain’s physical “neural switch” is broken. Without active signaling from the medial septum to the entorhinal cortex, the brain cannot default to the present, causing it to automatically slide back into old, deeply etched neural tracks.
A: The brain continuously operates on chronological sorting. When you have a new experience, like finding a better restaurant than the one you went to yesterday—the medial septum acts like an internal editor. It sends a targeted pulse to the entorhinal cortex to suppress the older memory trace and actively elevate the fresh, updated data to the hippocampus so you can make an informed, modern decision.
A: Yes, the study directly links memory accuracy to sustained brain rhythms. The longer the brain can preserve an “online state” powered by theta waves, the more efficiently it retrieves recent memories. If your brain constantly flickers back and forth between this focused online state and a resting, offline delta wave state, its internal filing system breaks down, drastically reducing your ability to remember recent events.
Editorial Notes:
- This article was edited by a Neuroscience News editor.
- Journal paper reviewed in full.
- Additional context added by our staff.
About this memory and neuroscience research news
Author: JEEHYUN LEE
Source: KAIST
Contact: JEEHYUN LEE – KAIST
Image: The image is credited to Neuroscience News
Original Research: Closed access.
“A septo–entorhinal GABAergic pathway that enables switching between episodic memories” by Mujun Kim, Boin Suh, Sunhoi So, Jung Wook Choi, Jaemin Hwang, Juhee Park & Jin-Hee Han. Nature Neuroscience
DOI:10.1038/s41593-026-02280-6
Abstract
A septo–entorhinal GABAergic pathway that enables switching between episodic memories
New experiences are integrated with existing knowledge to update memory, which is essential for survival in a dynamic environment. Despite this updating, the brain can still access previous memories to guide appropriate behavior. How the brain organizes the retrieval of old and new memories remains unknown.
Here we demonstrate a flexible memory switching mechanism in male mice, mediated by medial septum (MS) GABAergic neurons projecting to the medial entorhinal cortex (MEC).
This neuronal subset was specifically recruited during retrieval after updating, and inactivation of their projections to the MEC reversed the updated behaviors—indicating a behavioral switch to previous memories—and induced a switch in CA1 population activity patterns back to the pre-update pattern. After updating, the duration of the ‘online’ state correlated with memory performance.
Together, these findings reveal a neural switch mechanism mediated by the septo–entorhinal GABAergic pathway that organizes memory retrieval to enable updating.
