A coronal section in neuroanatomy refers to a vertical slice of the brain, typically oriented from ear to ear, similar to slicing a loaf of bread. The hippocampus, a neural structure located in the medial temporal lobe of each cerebral hemisphere, appears in this orientation. It is shaped like a curved ridge of gray matter, somewhat resembling a seahorse or a ram’s horn, which gave rise to its historical name, “Cornu Ammonis.”
Understanding the Coronal View
The coronal view offers a perspective for examining the hippocampus and its relationship with nearby brain regions. This orientation shows the hippocampus’s C-shaped structure as it folds into the medial temporal lobe. Observing the brain in coronal sections helps researchers and clinicians understand the three-dimensional organization of this deeply embedded structure.
Magnetic resonance imaging (MRI) utilizes coronal planes, often angled perpendicular to the hippocampus’s long axis, to visualize its details. This imaging approach identifies the hippocampus’s head, body, and tail, and its position relative to surrounding landmarks like the temporal horn of the lateral ventricle. Seeing these relationships in a cross-section is valuable for anatomical study and clinical diagnosis.
Key Anatomical Components in a Coronal Section
In a coronal section, the hippocampus reveals several subdivisions, each with a layered organization. The hippocampal formation includes the hippocampus proper, the dentate gyrus, and the subiculum. The hippocampus proper is divided into four Cornu Ammonis (CA) fields, labeled CA1, CA2, CA3, and CA4.
The dentate gyrus, often considered the main input channel for the hippocampal formation, appears as a narrow, toothed strip of gray matter. It comprises three layers: the molecular layer, the granular layer, and the polymorphic layer. Granule cells within the dentate gyrus receive signals from the entorhinal cortex and project their axons, known as mossy fibers, to the pyramidal cells in the CA3 region.
Following the dentate gyrus, the CA fields are visible, characterized by their densely packed pyramidal cell layers. CA3, the largest of these fields, receives input from the dentate gyrus and sends its axons to CA1. CA2 is a smaller region, while CA1 projects to the subiculum and deep layers of the entorhinal cortex. The subiculum, situated between CA1 and the entorhinal cortex, serves as a primary output region, collecting information from CA1 and transmitting it to various brain regions.
Functions of the Hippocampus
The hippocampus plays a role in several cognitive processes, particularly memory formation and spatial navigation. It is recognized for its involvement in converting short-term memories into long-term memories, a process known as memory consolidation. This includes declarative memory, which encompasses the recollection of facts and events, and episodic memory, relating to personal experiences.
Beyond its memory functions, the hippocampus is also involved in spatial memory, enabling spatial navigation and understanding one’s position. Research suggests that the hippocampus constructs “cognitive maps” of both physical and abstract spaces, which are used for navigation and for organizing relational memories. While often associated with spatial processing, the hippocampus’s role in navigation stems from its broader capacity for organizing experiences and relationships in memory.
Clinical Relevance and Conditions
The hippocampus is implicated in various neurological and psychiatric disorders, making its study in coronal sections relevant for clinical diagnosis and research. In Alzheimer’s disease, the hippocampus is one of the first brain regions to show damage, often exhibiting significant atrophy in its early stages. This tissue loss is associated with the short-term memory impairment and disorientation commonly observed in individuals with Alzheimer’s.
Temporal lobe epilepsy often involves hippocampal sclerosis, a condition characterized by damage and scarring within the hippocampus. Imaging techniques like MRI, which use coronal views, are valuable for detecting these structural changes, such as widening of the choroid fissure or temporal horn, and alterations in hippocampal volume and signal intensity. The hippocampus’s involvement extends to mood disorders, with studies showing a link between hippocampal volume loss and late-life depression, indicating a higher risk of cognitive decline in affected individuals. Additionally, abnormalities in hippocampal volume have been observed in conditions like schizophrenia and post-traumatic stress disorder (PTSD).