Hippocampus最新文献

A theory and network model are presented of how scene representations are built by forming spatial view cells in the ventromedial visual cortical scene pathway to the hippocampus in primates including humans. Layer 1, corresponding to V1–V4, connects to Layer 2 in the retrosplenial scene area and uses competitive learning to form visual feature combination neurons for the part of the scene being fixated, a visual fixation scene patch. In Layer 3, corresponding to the parahippocampal scene area and hippocampus, the visual fixation scene patches are stitched together to form whole scene representations. This is performed with a continuous attractor network for a whole scene made from the overlapping Gaussian receptive fields of the neurons as the head rotates to view the whole scene. In addition, in Layer 3, gain modulation by gaze direction maps visual fixation scene patches to the correct part of the whole scene representation when saccades are made. Each neuron in Layer 3 is thus a spatial view cell that responds to a location in a viewed scene based on visual features in a part of the scene. The novel conceptual advances are that this theory shows how scene representations may be built in primates, including humans, based on features in spatial scenes that anchor the scene representation to the world being viewed (to allocentric, world-based, space); and how gaze direction contributes to this. This offers a revolutionary approach to understanding the spatial representations for navigation and episodic memory in primates, including humans.

Early midlife bilateral salpingo-oophorectomy (BSO) is associated with greater Alzheimer's disease risk compared to spontaneous/natural menopause. Previously, we found that participants with BSO had lower volume in the hippocampal dentate gyrus and cornu ammonis 2/3 composite subfield (DG-CA2/3). We sought to extend those hippocampal subfield findings by assessing whether BSO affected volumes along the anteroposterior hippocampal axis, anterolateral entorhinal cortex, and perirhinal cortex subregions (Brodmann area (BA) 35 and 36). We also correlated volumes with key demographic and wellbeing-related factors (age, depressive mood, education), hormone therapy characteristics, and recognition memory performance. Early midlife participants with BSO (with and without 17β-estradiol therapy (ET)) and age-matched control participants with intact ovaries (AMC) completed high-resolution T2-weighted structural magnetic resonance imaging (MRI). Medial temporal lobe volumes and Remember-Know task recognition memory performance were compared between groups—BSO (n = 23), BSO + ET (n = 28), AMC (n = 34) using univariate analyses. Multivariate Partial Least Squares (PLS) analyses were used to examine how volumes related to demographic and wellbeing-related factors, as well as hormone therapy characteristics. Relative to BSO + ET, BSO had lower posterior hippocampal and DG-CA2/3 volumes but greater perirhinal BA 36 volumes. Compared to age, depressive mood, and education, ET was the strongest positive predictor of hippocampal volumes and negative predictor of perirhinal BA 36 volumes. For BSO + ET, hippocampal volumes were negatively related to ET duration and positively related to concurrent progestogen therapy. Relative to AMC, BSO had greater anterolateral entorhinal cortex and perirhinal BA 35 and BA 36 volumes. BSO groups (with and without ET) relied more on familiarity than recollection for successful recognition memory. BSO and ET may have distinct effects on medial temporal lobe volumes, with potential implications for memory processes affected by Alzheimer's disease risk.

The ability to form different neural representations for similar inputs is a central process of episodic memory. Although the dorsal dentate gyrus and CA3 have been indicated as important in this phenomenon, the neuronal circuits underlying spatiotemporal memory processing with different levels of spatial similarity are still elusive. In this study, we measured the expression of the immediate early gene c-Fos to evaluate brain areas activated when rats recalled the temporal order of object locations in a task, with either high or low levels of spatial interference. Animals showed spatiotemporal memory in both conditions once they spent more time exploring the older object locations relative to the more recent ones. We found no difference in the levels of c-Fos expression between high and low spatial interference. However, the levels of c-Fos expression in CA2 positively correlated with the discrimination index in the low spatial interference condition. More importantly, functional network connectivity analysis revealed a wider and more interconnected neuronal circuit in conditions of high than in low spatial interference. Our study advances the understanding of brain networks recruited in episodic memory with different degrees of spatial similarity.

Highly respected hippocampal neuroanatomist Ricardo Insausti died on the morning of December 26th, 2024. For the previous 2 years, he carried out a heroic battle with cancer while still teaching, collaborating, and writing. His research made huge contributions to the neuroscience of the medial temporal lobe, and he led efforts to bring consistent nomenclature to the hippocampal formation of the rodent, primate, and human brains.

As a teenager, Ricardo was part of the swimming team and enjoyed snorkeling and spearfishing when he went to the beach. He also liked Basque pelota, more as an observer than as a participant. During the weekends, he liked to play MUS, the most widely played card game in Spain that originated in the Basque country, with his older brother Jesús against his father, and his other brother Santos José. Ricardo's interest in biology was evident even as a child. But his interest in research began when he was 15 years old, when his high school biology teacher encouraged him, and other students, to do experiments and took them on field trips to, for example, collect water from puddles, which they later examined under the microscope searching for microorganisms.

He began his medical studies at the University of Navarra and early on took part in studies of the nervous system in the Department of Anatomy. He immediately fell in love with the human brain and began volunteering in the Department of Neurosurgery at the Hospital of Navarra. Two years before finishing his medical studies, he already began carrying out research for his Ph.D. on the rodent trigeminal somatosensory system, specifically investigating the pain pathways to the brainstem reticular formation, which he completed in 1978. During that summer, he worked for 3 months as a village doctor in Peralta, a small town in Navarra. Although brief, he always remembered this period of clinical service fondly.

Subsequently, Ricardo was obliged to do mandatory military service, which lasted 15 months. His service was carried out in the city of Valladolid, which is about 200 miles southwest of Pamplona. He did his service at the Military Hospital but also spent many afternoons in the Anatomy Department of the University of Valladolid, keeping up to date on scientific advances.

After he finished military service, he thought of pursuing a professional career as a neurosurgeon and combining it with basic research. To do so, he took a national exam that would allow him an internship in a hospital to specialize in neurosurgery. He passed the exam, but the Hospital of Navarra did not offer places in neurosurgery. This meant that he would have had to go to the Hospital of Zaragoza, 120 miles from Pamplona. Since he would not have been able to keep doing research at his university, he was faced with the difficult decision of pursuing being a neurosurgeon or doing research.

Ultimately, he decided to focus on basic brain research and to teach gross anatomy in

Grid and place cells typically fire at progressively earlier phases within each cycle of the theta rhythm as rodents run across their firing fields, a phenomenon known as theta phase precession. Here, we report theta phase precession relative to turning angle in theta-modulated head direction cells within the anteroventral thalamic nucleus (AVN). As rodents turn their heads, these cells fire at progressively earlier phases as head direction sweeps over their preferred tuning direction. The degree of phase precession increases with angular head velocity. Moreover, phase precession is more pronounced in those theta-modulated head direction cells that exhibit theta skipping, with a stronger theta-skipping effect correlating with a higher degree of phase precession. These findings are consistent with a ring attractor model that integrates external theta input with internal firing rate adaptation—a phenomenon we identified in head direction cells within AVN. Our results broaden the range of information known to be subject to neural phase coding and enrich our understanding of the neural dynamics supporting spatial orientation and navigation.

Long-term potentiation (LTP) is proposed to be the molecular mechanism underlying learning and memory in the brain. A key event for LTP is the influx of calcium into post-synaptic neurons via multiple ion channel control systems. One such system involves N-methyl-D-aspartate receptors (NMDARs), which were originally believed to be essential for LTP and new learning. Recent studies have demonstrated that hippocampal NMDARs are critical for learning new spatial information in a novel environment; however, when pre-training occurs prior to new spatial learning, these receptors are not needed. Additionally, researchers have shown that activation of voltage-gated calcium channels (VGCCs) and their associated calcium influx can induce LTP independent of NMDARs. These findings led to the idea that the amount of calcium required for learning in hippocampus depends on whether the new learning takes place in a novel or familiar environment, with a novel environment demanding greater calcium influx. It was hypothesized that to impair new learning in a familiar environment both NMDARs and VGCCs would need to be blocked. Long-Evans rats were trained in a three-phase version of the Morris water task, which included pre-training, new learning mass-training, and a probe test. Prior to mass-training, intrahippocampal VGCCs were blocked individually or in combination with NMDARs blockade to evaluate their effects on the rats learning and memory. The results showed that blocking both NMDARs and VGCCs simultaneously impaired new spatial learning with familiar information, whereas VGCC blockade alone did not.

The cover image is based on the article The Suprapyramidal and Infrapyramidal Blades of the Dentate Gyrus Exhibit Different GluN Subunit Content and Dissimilar Frequency-Dependent Synaptic Plasticity In Vivo by Christina Strauch et al., https://doi.org/10.1002/hipo.70002.