Summary: Working memory is the “mental scratchpad” that allows us to hold and manipulate information in real-time. A new study has identified a specific molecular pathway centered on the protein Munc13-1 that acts as a gatekeeper for this process.
The research reveals that for working memory to function, synapses must be able to temporarily “strengthen” their connections through calcium-dependent signaling. When this molecular mechanism fails, the brain loses its ability to update information, leading to the cognitive “looping” seen in neurodegenerative and neurodevelopmental disorders.
Key Facts
- The Munc13-1 Protein: This protein is responsible for “vesicular priming”—preparing the tiny pouches of neurotransmitters (vesicles) to be released from one neuron to the next.
- Synaptic Strengthening: The study focused on two processes: short-term facilitation and post-tetanic potentiation (PTP). These are brief bursts where a synapse becomes hyper-efficient at transmitting signals.
- Calcium Sensors: Munc13-1 uses two “sensors” to detect calcium: the C2B domain (calcium-phospholipid signaling) and the calmodulin pathway.
- The Maze Test: Mice with a mutated Munc13-1 protein (unable to bind to phospholipids) failed spatial memory tests, repeatedly returning to locations they had already cleared of rewards—a classic sign of broken working memory.
- Clinical Link: Mutations in the human version of this gene (UNC13A) are already linked to intellectual disabilities, suggesting this pathway is a major factor in human neurodevelopment.
Source: University of Barcelona
Working memory is a cognitive function that is essential for carrying out everyday activities and temporarily retaining information. This process enables us to understand information, learn and manage responses in a controlled manner — abilities that are often impaired in certain neurodegenerative diseases.
Now, a study published in Cell Reports has identified a molecular pathway in the brain that is crucial for the proper functioning of working memory.
The study, conducted using animal models, is led by Francisco José López-Murcia, a professor at the Faculty of Medicine and Health Sciences and the Institute of Neurosciences of the University of Barcelona (UBneuro), and a member of the Bellvitge Biomedical Research Institute (IDIBELL). The team led by Professor Nils Brose at the Max Planck Institute for Multidisciplinary Sciences (MPI-NAT, Göttingen, Germany) is also participating in the project.
How synapses prepare for neural transmission
Neurons do not always communicate at a constant rate. In many neural circuits, brief bursts of activity occur that temporarily strengthen synapses, allowing for more efficient transmission of information. Two such transient strengthening processes are short-term facilitation and post-tetanic potentiation (PTP), both of which are particularly prominent at mossy fibre synapses, which are thought to contribute to working memory.
At the molecular level, the team focused on studying the Munc13-1 protein, a key factor that prepares synaptic vesicles for the release of neurotransmitters, a process known as vesicular priming. The study demonstrates that Munc13-1 must be regulated by calcium via two complementary pathways: calcium-phospholipid signalling (via the C2B domain of Munc13-1) and the calcium-calmodulin pathway (via a region that binds to this protein).
Analysing the molecular sensors of the Munc13-1 protein
In animal models with these signalling pathways disrupted, the authors measured synaptic responses at mossy fibre synapses in the hippocampus during stimulation patterns that mimic physiological activity.
“The results show that when Munc13-1 was unable to detect calcium signals properly, the synapses lost much of their ability to temporarily strengthen during repeated activity,” says Francisco José López-Murcia, a professor at the Department of Pathology and Experimental Therapeutics at the UB.
“Disruption of the calcium-phospholipid signalling pathway increased the threshold for inducing post-tetanic potentiation and reduced its magnitude, suggesting that this pathway is particularly important for triggering strong short-term increases in synaptic transmission,” explains the researcher.
A maze of errors: when memory fails at the synapse
To study whether these synaptic alterations influence behaviour, the team assessed the animal models in a spatial working memory task (an eight-arm radial maze). Mice carrying the Munc13-1 mutation — which disrupts calcium-mediated binding to cell membrane phospholipids — showed pronounced deficits consistent with impaired working memory, such as repeatedly returning to reward locations after having obtained the reward.
“These results provide experimental evidence that working memory may depend not only on sustained neuronal activation, but also on transient, activity-dependent changes in synaptic transmission that temporarily retain information within neural circuits,” says López-Murcia.
The study also highlights the role of the Munc13-1 protein as a key component that enables synapses to sustain to adapt in order to transfer and reinforce information during peaks of activity, an essential feature of neuronal activity in the hippocampus.
By identifying a specific molecular mechanism that links short-term synaptic strengthening to working memory performance, this study expands our understanding of how the brain rapidly stores and updates information.
Previous studies have identified mutations in the human UNC13A gene that alter the sequence of multiple protein domains — including those examined in this study — in people with a wide range of neurological symptoms, notably intellectual disability. The findings of the new study highlight the crucial role of the Munc13-1 protein in healthy brain function and its clinical relevance in neurodevelopmental disorders.
Key Questions Answered:
A: Not quite. It’s more like “active” memory. If long-term memory is a library, working memory is the book you currently have open on the table. It allows you to remember the beginning of a sentence by the time you reach the end. This study shows that keeping that “book open” requires a physical strengthening of the synapse every time a signal passes through.
A: The synapse becomes “rigid.” Normally, if you use a synapse repeatedly, it should get stronger and faster (like a muscle). Without a working Munc13-1 protein to sense calcium, the synapse stays at a baseline level. This means the brain can’t prioritize or “tag” important incoming information, causing it to slip away almost immediately.
A: It’s a huge step forward. By identifying the exact “sensor” (the C2B domain) that triggers memory-related strengthening, scientists can now look for drugs that mimic or enhance that calcium-binding process. This could eventually help patients with neurodegenerative diseases where these synaptic “strengthening” bursts are depleted.
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: Rosa Martínez
Source: University of Barcelona
Contact: Rosa Martínez – University of Barcelona
Image: The image is credited to Neuroscience News
Original Research: Open access.
“Ca2+-phospholipid-dependent regulation of Munc13-1 is essential for post-tetanic potentiation at mossy fiber synapses and supports working memory” by Francisco José López-Murcia, Dilja Krueger-Burg, Sally Wenger, Tania López-Hernández, Noa Lipstein, Holger Taschenberger, and Nils Brose. Cell Reports
DOI:10.1016/j.celrep.2026.117029
Abstract
Ca2+-phospholipid-dependent regulation of Munc13-1 is essential for post-tetanic potentiation at mossy fiber synapses and supports working memory
Hippocampal mossy fiber (hMF) to CA3 pyramidal cell synapses are thought to support the formation of working memory through presynaptic short-term facilitation (STF) and post-tetanic potentiation (PTP). However, the molecular mechanisms underlying these transient forms of synaptic enhancement are unclear.
We show here that Munc13-1-mediated priming of synaptic vesicles at active zones controls hMF STF and PTP in response to Ca2+-phospholipid and Ca2+-calmodulin signaling.
Knockin mice expressing Munc13-1 variants insensitive to either signaling pathway exhibit pronounced deficits in STF and PTP, and the PTP induction threshold is markedly increased upon blockade of Ca2+-phospholipid-Munc13-1 signaling.
Since these synaptic defects are accompanied by working memory deficits, especially in mice expressing the Ca2+-phospholipid-insensitive Munc13-1 variant, we conclude that the Ca2+-dependent regulation of Munc13-1-mediated SV priming co-determines hMF short-term plasticity and working memory formation.
