Researchers have identified the neurons responsible for “memory of events/things” and the consequences of those events/things, deepening our understanding of how the brain stores and retrieves details of “what” happened and offering a new target for treating Alzheimer’s disease.
Memories include three types of details: spatial, temporal, and event-related, the “where, when, and what” of an event. Their creation is a complex process that involves storing information based on the meanings and outcomes of different experiences, and forms the basis of our ability to remember and recount them.
The study, published in the journal Nature in mid-August by researchers from the University of California, Irvine, is the first to reveal the role of specific cells in how the brain classifies and remembers new information, especially when it is associated with rewards or punishments.
“Understanding this process is crucial because it deepens our insights into the fundamental way our brains work, particularly in learning and memory,” said lead author Kei Igarashi, a consulting fellow and associate professor of anatomy and neurobiology. “Our findings shed light on the complex neural circuits that enable us to learn from our experiences and store these memories in an organized manner.”
lateral entorhinal cortex
Several parts of the brain work together to create the memories we carry with us every day to school, university, work, social life and sporting activities. The hippocampus and the cortex are two parts of the brain that work to give us memory. The lateral olfactory cortex is one of the intermediate regions that supports the interactions between the hippocampus and the cortex, and it houses neurons that proactively refer to past events in a familiar environment.
The lateral olfactory cortex is a major interactive partner of the hippocampus, poised to participate in contextual memory associations. Recent in vivo studies have shown that neurons in the lateral olfactory cortex encode odors, object novelty, object-to-space associations, contextual significance, temporal structure, and cue-to-reward associations.
The researchers studied the brains of mice, focusing on the deep layers of the lateral entorhinal cortex, where they discovered specialized neurons, related to remembering things and what they produce, and important for the learning process.
Odors are important sensory cues for object memory in mice. Some neurons became active when exposed to the odor of bananas, which were associated with the reward of sucrose water. Other neurons responded to the odor of pine, which was associated with the negative outcome of bitter water. A mental map divided into these two categories was formed in the lateral entorhinal cortex.
medial prefrontal cortex
Anatomically, neurons in the deep layer of the lateral entorhinal cortex are closely connected to neurons in another region of the brain, the medial prefrontal cortex. The team members noticed that neurons in the medial prefrontal cortex developed a similar mental map during the learning process.
They also found that when the activity of neurons in the lateral entorhinal cortex was inhibited, those in the medial prefrontal cortex failed to correctly discriminate between positive and negative items, resulting in impaired learning.
Conversely, when neurons in the medial prefrontal cortex were inhibited, the ability of the lateral entorhinal cortex to hold memories of separate items was completely disrupted, resulting in impaired learning and retrieval of object/event memory. These data suggested that the lateral entorhinal cortex and the medial prefrontal cortex are mutually dependent and work together to encode object/event memory.
“This study represents a major advance in our understanding of how item memory is created in the brain, and this knowledge now opens up new avenues for studying memory disorders such as Alzheimer’s disease,” Igarashi said, according to EurekAlert.
“Our data suggest that object/event memory neurons in the lateral entorhinal cortex lose activity in Alzheimer’s disease,” he added. “If we can find a way to reactivate these neurons, it could lead to targeted therapeutic interventions.”