Hungarian Researchers Uncover New Insights into a Key Brain Region

13.03.2025

The hippocampus plays a crucial role in learning and memory and is associated with numerous neurological and psychiatric disorders. While extensive data exist on the structure of the hippocampus in rodents, our understanding of its human counterpart remains incomplete. Researchers at the HUN-REN Institute of Experimental Medicine (HUN-REN IEM) have now identified key cell groups within different layers of the human hippocampus. Their findings could significantly advance research into conditions such as schizophrenia, epilepsy, and Alzheimer’s disease.

The hippocampus is an ancient cortical structure essential for learning and memory. Its main function is to store and retrieve consciously accessible memories, typically in verbal form. For example, it enables us to recall the location of our favourite coffee shop when visiting a town we have not been to in a long time.

To gain a deeper understanding of hippocampal function, researchers require computational models based on precise quantitative data, including the number of cells in different cell groups and their synaptic connections. While extensive numerical data exist on the neuronal composition and synaptic architecture of the rodent hippocampus, similar knowledge of the human hippocampus remains scarce. This gap in understanding is partly due to the difficulty of obtaining well-preserved brain samples, which must be collected within 3.5 hours of death—an exceedingly challenging criterion to meet.

A research group at HUN-REN IEM, led by Gábor Nyiri, used stereological methods to estimate the total number of cells in three major inhibitory cell groups across different layers of the human hippocampus. They also employed three-dimensional electron microscopy to determine the total number of inhibitory synapses within the hippocampus. The high-quality samples required for these studies were obtained with the support of the HUN-REN IEM Human Brain Tissue Laboratory and the Pathology Department of Szent Borbála Hospital in Tatabánya.

These findings provide essential data for modelling the networks of the human hippocampus and understanding its complex regulatory dynamics, which are key to unravelling its function. This research may also advance studies on diseases such as schizophrenia, epilepsy, and Alzheimer's disease, as these conditions are linked to interneuron dysfunction. Given that many neurological and psychiatric disorders are associated with inhibitory neuron groups in this brain region, a deeper understanding of hippocampal function is crucial for developing more effective therapies.

The study by HUN-REN IEM researchers is featured on the cover of the March issue of The Journal of Neuroscience.

IEM hippocampus — Parvalbumin-positive interneurons in the pyramidal layer of the CA1 region of the hippocampus.

HUN-REN aims to become one of the most effective research organisations in Europe and to contribute significantly to Hungary's social and economic success. The HUN-REN Act, effective from 1 January 2025, provides the necessary framework for HUN-REN to transform into a more responsive, collaborative, performance-oriented, and well-functioning network, ensuring the freedom of scientific research and the continuation of exploratory research, while providing multidisciplinary solutions to complex challenges affecting both national and international communities. Employees within the modernising HUN-REN can look forward to a long-term, consistent, value-driven, and performance-focused funding system, mutually reinforcing structure and operation, competitive salaries, and a predictable research career.