Scientists Clarify How the Brain Memorises and Recalls Information
An international team, including scientists from HSE University, has demonstrated for the first time that the anterior and posterior portions of the human hippocampus have distinct roles in associative memory. Using stereo-EEG recordings, the researchers found that the rostral (anterior) portion of the human hippocampus is activated during encoding and object recognition, while the caudal (posterior) portion is involved in associative recall, restoring connections between the object and its context. These findings contribute to our understanding of the structure of human memory and may inform clinical practice. A paper with the study findings has been published in Frontiers in Human Neuroscience.
Associative memory is the ability to link various elements of information—such as objects, events, sensations, and contexts—based on shared perceptions or semantic connections. It helps us remember not only what we saw, but also where, when, and in what context it occurred. The hippocampus, a brain structure located in the temporal lobe and responsible for the formation and retrieval of episodic memories, plays a crucial role in these processes by integrating fragments of information into a coherent representation of the event.
Until now, it has remained unclear exactly how functions are distributed between the anterior and posterior parts of the human hippocampus, particularly in relation to associative memory. Previous studies have indicated functional differences between regions of the hippocampus in animal models; however, how these differences manifest in humans has not yet been investigated experimentally.
Researchers from HSE University, the University of Zurich, and the Swiss Epilepsy Centre conducted an experiment involving patients with epilepsy. For medical reasons, these patients were implanted with depth electrodes (stereo-EEG), which directly record activity from the brain's internal structures. This allows for precise measurement of the functioning of different parts of the hippocampus (HC).
The experiment was conducted in two sessions. In the first session, participants were shown pairs of images: one depicting an object and the other depicting a scene. Participants were then asked to rate the logical congruence of each object–scene pair—for example, book—library, earplugs—living room, or beach ball—laboratory. These pairs were used to study how context influences memory.
The following day, participants were shown both familiar and new objects and asked to identify which ones they had seen before and recall the context in which each item had previously appeared. The goal was to assess how well participants remembered both the objects and the contexts in which they had seen them.
The researchers found that the anterior and posterior portions of the hippocampus are responsible for distinct aspects of memory function. The anterior part was more active when participants memorised the object–scene pairs and during the subsequent recognition of these objects, indicating its role in forming new associations and recognising familiar items.
In contrast, the posterior part of the hippocampus was activated when participants recalled which object was associated with which scene. It was particularly active in cases where the object–scene pairings were not obvious—not absurd but also not entirely congruent. This finding underscores the importance of the posterior hippocampus in searching for semantic connections and retrieving complex information from memory.
'We were able to accurately describe how different regions of the hippocampus coordinate their roles in encoding and recalling information. This enables us to better understand the mechanisms of human memory and opens up new possibilities for helping people with memory impairments,' explains Alisia Vorobyova, Associate Professor at the School of Psychology of the HSE Faculty of Social Sciences and co-author of the study.
The study findings not only clarify fundamental aspects of brain function but may also have important implications for clinical practice. Understanding which regions of the hippocampus are involved in different types of memory can help clinicians evaluate the effects of epilepsy surgery more accurately. In addition, these findings could inform the development of new approaches to rehabilitating patients with cognitive impairments.
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