The University of Maryland, Baltimore County announced on Apr. 10 new research showing that two distinct parts of the brain's memory center work together in a key reward region to help mice—and likely humans—combine memories of places and contexts with the drive to pursue rewards.
This discovery provides new insight into how the brain brings together information about location and pleasurable experiences to inform everyday decisions, such as choosing where to eat or seeking enjoyable activities. The findings, published in the Journal of Neuroscience, indicate that inputs from both the dorsal and ventral hippocampus converge on individual neurons within another brain region called the nucleus accumbens, where they interact in ways that amplify each other's effects.
Previously, scientists believed connections from these two hippocampal regions—the dorsal hippocampus linked with spatial memory and navigation, and the ventral hippocampus associated more closely with emotions and motivation—remained mostly separate. This study challenges that understanding by demonstrating their close interaction at a cellular level. "A single neuron can receive inputs from different brain regions, and figuring out how it integrates them is crucial for understanding what drives goal-directed actions," LeGates says.
Researchers used advanced techniques such as optogenetics (using light to stimulate specific pathways), electrical recordings from neurons, and detailed microscope imaging. They identified a group of neurons in part of the accumbens receiving direct input from both hippocampal areas. These synapses were found extremely close together—often within just a couple microns—on branches of dendrites resembling tree roots on nerve cells. When both pathways are active simultaneously, they produce a stronger combined response than either alone.
Ashley Copenhaver led much of this work: "One of the most exciting parts of this technically challenging project was performing dual-color optogenetics during electrophysiology—I was literally shining tiny beams of red and blue light onto brain tissue... It was magical," Copenhaver says. "Beyond loving the technique... we identified some really critical and fundamental mechanisms of signal integration within the brain. I'm super excited to see where this work heads next." LeGates adds that signals from both parts are “probably converging more than we've previously appreciated,” which could influence future research into motivation and learning.
The researchers note this convergence may help animals form associations between rewarding outcomes and their environments—a vital skill for survival—and similar patterns have been observed elsewhere in emotional learning circuits. Looking ahead, LeGates' lab plans further studies on how stress or substances like food or drugs affect these neural connections with hopes for improved treatments for mental health conditions.
