Summary: Researchers have identified the world’s first neural “switch” that helps the brain prioritize recent memories over older ones. The team found a specific circuit linking the medial septum (MS) and the medial entorhinal cortex (MEC) that actively determines whether the brain uses up-to-date information or falls back on older behavioral patterns.
This discovery clarifies how the brain preserves cognitive flexibility and suggests new therapeutic directions for conditions such as dementia and Alzheimer’s disease, in which patients frequently become fixed on older memories.
Key Facts
- The Septo–Entorhinal Circuit: A distinct pathway from the medial septum to the medial entorhinal cortex functions as a switch that influences which memories are retrieved and forwarded to the hippocampus.
- Active Chronological Selection: Memory retrieval is regulated, not just passively replayed. This circuit evaluates competing memories and promotes the most recent, context-relevant information.
- Regression Effect: When researchers disrupted this pathway experimentally, animals could no longer use recently acquired information and reverted to older behavioral routines; hippocampal activity patterns also shifted back to a pre-update state.
- Rhythm-Dependent Retrieval: Successful selection of recent memories depends on maintaining an “online” brain state marked by theta oscillations. Frequent switching into “offline” delta states impairs the ability to recall recent events.
Source: KAIST
“Why do patients with dementia or cognitive decline remain stuck in past memories?”
A research team led by Professor Jin-Hee Han at KAIST has demonstrated, for the first time, a neural mechanism that selectively retrieves recent episodic memories. They show that a subset of GABAergic neurons in the medial septum projects to the medial entorhinal cortex and functions as a flexible switch that biases retrieval toward updated information.
Everyday decision-making depends on updating stored knowledge with new experiences. For example, if a restaurant visited today is better than one from yesterday, the brain should update its memory and preference accordingly. The ability to prefer new, relevant information over older traces underlies higher cognitive functions such as planning, reasoning, and flexible problem-solving. Until now, the mechanism that governs this chronological selection was not well understood.
The researchers focused on the medial septum, a deep brain region that orchestrates hippocampal rhythms and acts like a conductor for memory-related neural activity. They found that when specific medial septum neurons send targeted signals to the medial entorhinal cortex — a major interface with the hippocampus — the brain reliably retrieves more recent memories. When that pathway was inhibited experimentally, subjects reverted to older behavioral patterns and neural activity in the hippocampus returned to its prior configuration, demonstrating the circuit’s role as a switch for selecting recent information.
The study also explored how brain states affect retrieval. The brain alternates between an “online” state, dominated by theta waves and associated with attention and learning, and an “offline” state marked by slower delta waves that occur during rest. The researchers observed that maintaining the online, theta-dominant state improved recall of updated memories, while rapid toggling between online and offline states reduced retrieval performance. These results highlight that not only structure but also rhythmic brain states are essential for effective memory access.
Beyond basic neuroscience, these findings have practical implications. Identifying a biological switch that biases memory retrieval toward recent experiences creates a target for therapies aiming to restore cognitive flexibility. For patients with degenerative brain conditions, interventions that restore or mimic this septo–entorhinal signaling and stabilize theta-dominant states could help reduce pathological fixation on remote memories and improve daily functioning.
Professor Jin-Hee Han commented that this research reframes how we understand memory retrieval: rather than passive playback, the brain actively selects among competing memories in chronological order. The medial septum–entorhinal pathway acts as a regulatory mechanism that elevates fresh, context-relevant traces over older ones.
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: The study suggests that in degenerative conditions, the problem may not be that recent memories are permanently lost but that the neural circuitry that promotes retrieval of up-to-date information is impaired. When the medial septum’s signaling to the entorhinal cortex weakens, the brain defaults to older, strongly encoded neural pathways, making recent events hard to access.
A: The brain prioritizes memories chronologically and contextually. When you form a new, more relevant experience, the medial septum sends targeted input to the entorhinal cortex that suppresses older traces and promotes the updated memory to the hippocampus, enabling behavior that reflects current information.
A: The findings link memory accuracy to sustained theta rhythms. Maintaining an online, theta-dominant state enhances retrieval of recent memories, while frequent transitions to an offline delta state impair the brain’s ability to access newly updated information.
Editorial Notes:
- This article was edited by a Neuroscience News editor.
- The journal paper was reviewed in full.
- Additional context was 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
Adapting to new experiences requires integrating fresh information with existing knowledge so memories can be updated while still allowing access to older memories when needed. How the brain manages retrieval of old versus new memories has been unclear. This study demonstrates a flexible memory switching mechanism in male mice mediated by medial septum GABAergic neurons that project to the medial entorhinal cortex. These neurons are recruited specifically during retrieval after updating. Inactivation of their projections to the MEC reverses updated behavior, producing a behavioral switch back to previous memories and causing CA1 hippocampal population activity to revert to pre-update patterns. After updating, the duration of the online state correlates with memory performance. Together, these results identify a septo–entorhinal GABAergic pathway that acts as a neural switch organizing memory retrieval to enable updating.