A groundbreaking study published in Cell Reports has identified a critical molecular “hub” in the brain that allows us to hold information temporarily, a process known as working memory.

The work is led by Dr. Francisco José López-Murcia, Assistant Professor at the Faculty of Medicine and Health Sciences, member of the Institute of Neurosciences of the University of Barcelona (UBneuro), and researcher at the Bellvitge Biomedical Research Institute (IDIBELL). The project has been performed together with colleagues from Prof. Nils Brose’s lab, at the Max Planck Institute for Multidisciplinary Sciences (MPI-NAT, Göttingen, Germany).

Synaptic Vesicles Priming allows Synaptic Detonation: How Synapses Prep for Action

Neurons don’t always communicate at a constant rate. In many circuits, brief bursts of activity temporarily strengthen synapses, allowing information to be transmitted more efficiently. Two of these transient strengthening processes are short-term facilitation and post-tetanic potentiation (PTP), both particularly prominent at mossy fiber synapses, which are thought to support working memory.

At the molecular level, the team focused on Munc13-1, a key protein that prepares synaptic vesicles for neurotransmitter release (a step often referred to as vesicle priming). The study demonstrates that Munc13-1 must be regulated by calcium through two complementary pathways:

  • Calcium–phospholipid signaling (via the C2B domain of Munc13-1).
  • Calcium–calmodulin signaling (via a calmodulin-binding region).

Dissecting the Molecular Sensors of Munc13-1

Using two genetically engineered mouse models with targeted changes in Munc13-1, each disrupting one of the calcium-dependent regulatory pathways, the authors measured synaptic responses at hippocampal mossy fiber synapses during patterns of stimulation that mimic physiological activity. They found that when Munc13-1 could not properly “sense” calcium signals, synapses lost much of their ability to temporarily strengthen during repeated activity.

Importantly, disruption of calcium–phospholipid regulation raised the threshold for inducing PTP and reduced its magnitude, indicating that this pathway is especially important for triggering strong short-term boosts in synaptic strength.

A Maze of Errors: When Memory Fails at the Synapse

To explore whether these synaptic alterations matter for behavior, the researchers assessed animals in a spatial working-memory task (an 8-arm radial maze). Mice carrying the Munc13-1 mutation that disrupts calcium–phospholipid regulation showed pronounced deficits consistent with impaired working memory, such as repeatedly returning to reward locations after the reward had already been collected.

These results provide experimental support for the idea that working memory may depend not only on sustained neural firing, but also on transient, activity-dependent changes in synapticstrength that temporarily “hold” information in neural circuits.

Why it matters

By identifying a concrete molecular mechanism that links short-lived synaptic strengthening to working-memory performance, this work advances our understanding of how the brain rapidly stores and updates information. It also highlights Munc13-1 as a central hub that helps synapses adapt to bursts of activity, an essential feature of hippocampal computation.

Importantly, mutations in the human gene UNC13A that alter the sequence of multiple protein domains, including those examined in this study, have been identified in individuals with a broad spectrum of neurological symptoms, prominently including intellectual disability. Together, these findings underscore Munc13-1 as a key determinant of healthy brain function and highlight its clinical relevance in neurodevelopmental disorders.