New research from the University of Maryland, Baltimore County (UMBC) reveals how two different parts of the brain’s memory center work together in a key reward region to help mice—and potentially humans—associate memories of places and environments with the desire to seek rewards.
The findings offer new insight into how the brain integrates information about “where” and “what feels good” to guide everyday decisions, such as going to a favorite restaurant to meet friends or seeking out rewarding experiences. Specifically, this discovery, published in the Journal of Neuroscience, shows that inputs from the dorsal and ventral hippocampus converge on the same individual neurons in another brain region, the nucleus accumbens, where they interact in ways that amplify each other’s effects.
The connection between the hippocampus and the nucleus accumbens is where the brain’s map of where to go meets the sense of why it’s worth going.”
Tara LeGates, senior author, assistant professor in UMBC’s Department of Biological Sciences
For years, scientists saw the connections from the dorsal hippocampus, which is more closely linked to spatial memory and navigation, and the ventral hippocampus, which is more strongly linked to emotion and motivation, as mostly separate. This paper challenges this understanding.
“A single neuron can receive inputs from different areas of the brain, and understanding how it integrates them is critical to understanding what drives goal-directed actions,” says LeGates.
While the current study focuses on single cells, the implications reach further. A better understanding of how these reward-related circuits process and combine information could shed light on conditions where motivation is disrupted, such as depression, addiction or anxiety disorders.
A close-up of the convergence
The research team used advanced methods, including using light to stimulate specific pathways (a technique called optogenetics), precise recordings of electrical activity in neurons, and detailed microscope imaging to identify a group of neurons in a specific part of the epiclinum that receives direct input from both the dorsal and ventral hippocampus.
Importantly, the synapses involved in these two pathways are very close to each other—often within a few microns (millimeters of a millimeter)—on the same branches of the neurons’ dendrites, which resemble tree roots in nerve cells. This proximity allows them to quickly influence each other. The team found that when both inputs are active at the same time, they produce a stronger combined response than either alone.
The researchers worked with Tagide deCarvalho, director of UMBC’s Keith Porter Imaging Facility, to obtain the high-resolution imaging that confirmed these close collaborations. Upgraded software at the facility allowed the team to capture ultra-thin digital slices (0.2 microns thick) and create 3D reconstructions of neuronal branches, clearly demonstrating the close proximity of synapses that would allow them to interact.
The study’s first author, Ashley Copenhaver, Ph.D. ’25, neuroscience and cognitive science, led much of the hands-on work on the recordings and imaging while mentoring the undergraduate team members.
“One of the most exciting parts of this technically challenging project was optogenetic dichroism during electrophysiology—I was literally shooting tiny beams of red and blue light into brain tissue, which activated dorsal or ventral hippocampal neurons, so I could record the electrical responses in the afferent neurons. magical“Beyond the love of the technique, I think we’ve identified some really critical and fundamental mechanisms of signal integration in the brain. I’m very excited to see where this work goes.”
From cells to behavior
Understanding how a single neuron handles signals from different areas of the brain is key to understanding complex behaviors, says LeGates, who holds a postdoctoral appointment in the Department of Pharmacology and Physiology at the University of Maryland School of Medicine. Signals from the dorsal and ventral hippocampus “probably converge more than we previously appreciated, which could change the way people approach questions about motivation and learning,” he adds.
This kind of convergence likely helps animals form associations between rewarding outcomes and the environments where they occur—an essential skill for survival. Similar convergence has been observed in other brain regions involved in emotional learning, LeGates says, suggesting that the brain can use this strategy broadly to associate a particular context with emotion and action.
LeGates’ lab is already building the foundation of this work by investigating how stress and substances such as food, medication and illicit drugs affect these same connections, with the long-term goal of informing more targeted treatments for various mental health conditions. In the near future, the team hopes to record activity from these specifically connected neurons during real behaviors to directly link the newly discovered crosstalk between the ventral and dorsal hippocampus to actions.
By revealing this hidden layer of cooperation between hippocampal pathways, the LeGates lab has advanced our understanding of how the brain combines memory and motivation—a fundamental process that shapes the decisions that lead to everyday life.
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