Reviewed by Lexie CornerApr 1 2025
Researchers at the Janelia Research Campus, Howard Hughes Medical Institute, have developed a new method to map changes in individual neuronal connections across the brain during learning, offering scientists a new insight into how behavioral changes manifest in the brain.
A new imaging method, DELTA, provides scientists with a brain-wide map of how individual synaptic proteins change over time. This schematic shows how DELTA works. Before the injection of the pulse dye, all proteins are unlabeled (gray line). After injection of the pulse dye (dashed green line), all proteins are labeled with the pulse dye (solid green line). During the pulse-chase interval, some proteins degrade, and others are synthesized but unlabeled. Injection of a spectrally separate dye (dashed magenta line) binds the newly synthesized protein (solid magenta line). Image Credit: Mohar et al.
Synapses are microscopic junctions where neurons exchange brief signals with each other. Experiences lead to changes in the strength of these connections, a process known as synaptic plasticity, which is fundamental to learning and memory. However, little is known about the precise location of these changes in the brain during the learning process.
To identify where these synaptic changes occur in the brain, researchers at Janelia have developed a new method. The project, led by the labs of former Janelia Senior Group Leader Karel Svoboda, Spruston, and Lavis, has resulted in a new imaging technique called DELTA.
This technique allows scientists to observe how individual synaptic proteins change over time across the entire brain. Proteins critical for synaptic plasticity are either synthesized or degraded in response to changes in synaptic connections. By tracking these protein changes, scientists can learn how synaptic connections evolve during learning.
The new method provides insights into specific brain regions crucial for memory and learning and helps identify the molecular processes involved in synaptic changes.
One of the problems in figuring out which molecules are in charge of what changes is that it is very hard to know where those changes are happening. We did not have a good way of figuring out where in the brain things are changing so we can focus our attention on the most interesting parts. Now, we have a different way of looking at our manipulations and how they affect the circuit at the brain-wide level by using imaging to drill down on the subcellular structure. This helps us bridge that gap between behavior and mechanism.
Boaz Mohar, Research Scientist, Spruston Lab, Howard Hughes Medical Institute
The technique starts by applying a bright Janelia Fluor (JF) dye to a synaptic protein of interest in the mouse brain. To observe how synaptic connections change during learning, the researchers used mice trained on a simple task, learning to associate two distinct visual cues with a water reward.
After the initial labeling, the mice were divided into two groups: one group continued receiving random water at both cues, as they had before labeling, while the other group had the task modified so that only one of the cues was linked to the water reward.
A few days later, once the researchers observed differences between the groups, the same synaptic protein of interest was labeled with a different JF dye in both groups.
During this time, some of the initially labeled proteins degraded, while new proteins containing the second dye were synthesized. By imaging the entire brain, researchers could track where changes in synaptic connections occurred during learning by observing the locations of the altered synaptic proteins.
The researchers specifically studied the synaptic protein GluA2, which changed in certain brain regions as the mice learned the modified task.
Using this technique, the team also detected variations in protein turnover between mice in a standard setting and those in an enriched environment with toys and social interaction. Exposure to the enriched environment resulted in significant changes in GluA2 across the brain.
DELTA offers a foundation for future studies, enabling researchers to explore the cellular and molecular mechanisms behind learning and memory by tracking brain-wide changes.
To better pinpoint when proteins change during the learning process, the researchers are working to enhance DELTA with additional features.
Nelson Spruston, one of the lab heads overseeing the project, highlighted that DELTA’s development is an example of Janelia’s collaborative environment, with contributions from experts in chemistry, imaging, behavior, and genetics. The team also collaborated with external specialists, such as researchers from Northwestern University, to validate the approach.
Thanks to Janelia's Visiting Scientist Program, the team is now supporting researchers worldwide in using DELTA to monitor synaptic changes in their own studies.
This is a quintessential Janelia project. It involved doing something that nobody has ever done before and required collaboration with lots of people who contributed expertise to make this all possible.
Boaz Mohar, Research Scientist, Spruston Lab, Howard Hughes Medical Institute
New imaging tool maps brain-wide changes in neuronal connections
Imaging of single synapses in layer 1 of the cortex and in CA3 subfield of the hippocampus using ExM and Airyscan imaging. Video Credit: Mohar et al.
Journal Reference:
Mohar, B., et al. (2025) DELTA: a method for brain-wide measurement of synaptic protein turnover reveals localized plasticity during learning. Nature Neuroscience. doi.org/10.1038/s41593-025-01923-4.