Brain cell breakthrough could clarify excessive appetite

Researchers have uncovered a particular cluster of brain cells responsible for encoding meal memories, not just detailing which food was consumed but also when it took place. The results, published in Nature Communications, might illuminate why individuals with memory difficulties often overindulge and how forgetting about a recent meal can induce extreme hunger.

During consumption, neurons located in the brain’s ventral hippocampus become activated and generate what the research team refers to as “meal engrams” — specific memory traces that encapsulate data about the experience of eating. Long studied for their function in memory storage and other experiences, this new investigation highlights engrams specifically tied to meal events.

“An engram represents the tangible mark that a memory leaves within the brain,” stated Scott Kanoski, a professor of biological sciences at the USC Dornsife College of Letters, Arts, and Sciences and lead author of the research. “Meal engrams operate similarly to intricate biological databases that retain various types of information such as location and timing of consumption.”

Consequences of distracted eating

This finding is particularly pertinent for comprehending human eating disorders. Individuals with memory deficits, such as those suffering from dementia or brain injuries that hinder memory formation, often find themselves eating multiple meals in rapid succession due to their inability to recall previous meals.

Moreover, distracted eating—such as mindlessly snacking while watching a show or scrolling through a mobile device—can disrupt meal memories and lead to overeating.

Based on the study’s results, meal engrams form during brief intervals between bites while laboratory rats instinctively survey their eating surroundings. These moments of focus enable specialized hippocampal neurons to amalgamate diverse streams of information.

Kanoski posits that a human brain likely undergoes a similar process. When one’s attention is diverted—toward a mobile device or TV—these crucial encoding moments are impaired. “The brain struggles to accurately capture the meal experience,” explained Lea Decarie-Spain, a postdoctoral scholar at USC Dornsife and the study’s primary author, “resulting in weak or incomplete meal engrams.”

Kanoski asserts that human brains probably possess specialized memory systems for meals, as these occurrences are among the most critical to remember, “especially for lower-order mammals and the primates from which we evolved, who constantly sought reliable sources of sufficient energy. A meal engram is multimodal, since encoding and recalling eating-related data necessitate the convergence of interoceptive (internal), exteroceptive (visual and spatial data), and temporal cues (when was food last ingested). The hippocampus, particularly the ‘ventral’ segment that we are examining, is optimally positioned to assimilate these multimodal signals to construct coherent memories for meals, which aid in reliable foraging and consumption to maintain energy equilibrium.”

Mechanism behind ‘meal memories’

The research team utilized advanced neuroscience methodologies to monitor the brain activity of lab rats while they fed, shedding light on the real-time process of how meal memories develop.

The specialized meal memory neurons differ from brain cells involved in various types of memory formation. When researchers selectively destroyed these neurons, laboratory rats displayed impaired memory for food locations while maintaining normal spatial recollection for unrelated tasks, indicating a unique system dedicated to processing meal-related information. The study discovered that meal memory neurons have communication links with the lateral hypothalamus, a brain area historically recognized for regulating hunger and eating behavior. When this hippocampus-hypothalamus connection was interrupted, laboratory rats overconsumed and were unable to recall where their meals were eaten.

Significance for eating management

Kanoski noted that these findings could one day inform innovative clinical strategies for addressing obesity and weight maintenance. Current weight management tactics typically focus on reducing food intake or boosting physical activity, but the new research indicates that improving meal memory formation could be of equal significance.

“We are finally starting to recognize that remembering what and when you consumed is just as vital for healthy eating as the food choices themselves,” Kanoski remarked.

About the study: In addition to Kanoski, other contributors to this research include Lea Decarie-Spain, Cindy Gu, Logan Tierno Lauer, Alicia E. Kao, Iris Deng, Molly E. Klug, Alice I. Waldow, Ashyah Hewage Galbokke, Olivia Moody, Kristen N. Donohue, Keshav S. Subramanian, Serena X. Gao, Alexander G. Bashaw, and Jessica J. Rea of USC; along with Samar N. Chehimi, Richard C. Crist, Benjamin C. Reiner, and Matthew R. Hayes from the University of Pennsylvania’s Perelman School of Medicine; and Mingxin Yang and Guillaume de Lartigue from the Monell Chemical Senses Center; and Kevin P. Myers from the Department of Psychology at Bucknell University.

The study received support from a Quebec Research Funds Postdoctoral Fellowship (315201), an Alzheimer’s Association Research Fellowship (AARFD-22-972811), a National Science Foundation Graduate Research Fellowship (DK105155), and a National Institute of Diabetes and Digestive and Kidney Diseases grant (K104897).