Researchers at the University of Bonn have identified two distinct groups of neurons in the human brain that separately encode memory content and context. Their findings, published in Nature, provide new insights into how humans can remember the same person or object across different situations.
The study involved patients with drug-resistant epilepsy who had electrodes implanted in their hippocampus and nearby regions for diagnostic purposes. During their hospital stay, these patients participated in experiments where they compared pairs of images on a laptop based on various questions. This setup allowed researchers to observe how the brain processes identical images under different task contexts.
"We already know that deep in the memory centers of the brain, specific cells, called concept neurons, respond to this friend, regardless of the environment in which he appears," said Prof. Florian Mormann from the Clinic for Epileptology at UKB and member of the Transdisciplinary Research Area (TRA) "Life & Health" at the University of Bonn.
Dr. Marcel Bausch, working group leader at the Department of Epileptology and also a TRA "Life & Health" member, explained: "We asked ourselves: Does the human brain function fundamentally differently here? Does it map content and context separately to enable a more flexible memory? And how do these separate pieces of information connect when we need to remember specific content according to context?"
By analyzing over 3,000 neurons, researchers found that content neurons responded to particular images regardless of task instructions, while context neurons fired based on specific task contexts regardless of image shown. In contrast to rodent studies where individual neurons often mix both types of information, very few human neurons encoded both simultaneously.
"A key finding was that these two independent groups of neurons encoded content and context together and most reliably when the patients solved the task correctly," said Bausch.
As participants continued with tasks during the experiment, connections between content and context neuron groups became stronger. The firing pattern suggested that activity in a content neuron could predict subsequent activity in a context neuron within milliseconds. "It seemed as if the 'biscuit' neuron was learning to stimulate the 'Bigger?' neuron," said Mormann.
This coordinated activity supports what is known as pattern completion—the process by which partial cues help reconstruct full memories. According to Bausch: "This division of labor probably explains the flexibility of human memory: the brain can reuse the same concept in countless new situations without needing a specialized neuron for each individual combination, by storing content and context in separate 'neural libraries.'" Mormann added: "The ability of these neuronal groups to link spontaneously allows us to generalize information while preserving the specific details of individual events."
The study primarily examined interactive contexts created by specific questions during computer-based tasks but noted that passive background contexts—such as being in a particular room—might be processed differently. Researchers say further studies are needed outside clinical settings and suggest future work will explore whether disrupting interactions between these neuron groups affects memory retrieval or decision-making accuracy.
