The entorhinal cortex is a significant brain region involved in various cognitive functions. It serves as a crucial interface, facilitating communication between the hippocampus and other parts of the brain. Its role provides insights into how the brain processes information for memory and navigation.
Precise Anatomical Placement
The entorhinal cortex (EC) is located within the medial temporal lobe. It forms part of the rostral parahippocampal gyrus. This placement positions the entorhinal cortex adjacent to other structures, including the hippocampus and the perirhinal cortex.
The entorhinal cortex is a bilateral structure, present in both hemispheres of the brain. It is divided into two main subfields: the medial entorhinal cortex (MEC) and the lateral entorhinal cortex (LEC). These subdivisions have distinct properties and connections. The entorhinal cortex occupies the medial temporal region and includes parts of the parahippocampal gyrus.
Central Role in Brain Networks
The entorhinal cortex functions as a central hub for information flow within the brain’s memory and navigation systems. It serves as the primary gateway between the hippocampus, a structure for memory formation, and the neocortex, which handles higher-level cognitive processes. This position allows it to integrate processed sensory and cognitive information from various cortical areas.
The perforant path originates from the superficial layers of the entorhinal cortex and projects directly to the dentate gyrus and hippocampus. This pathway is the major route for cortical input to the hippocampus, making the entorhinal cortex essential for relaying information into the hippocampal formation. Output from the hippocampus returns to the deep layers of the entorhinal cortex, which then project back to the neocortex.
Core Functions in Memory and Navigation
The entorhinal cortex plays a significant role in both spatial navigation and the formation of new memories. The medial entorhinal cortex (MEC) is particularly involved in spatial processing, housing specialized neurons that contribute to an internal “GPS” system.
These specialized neurons include grid cells, which fire in a hexagonal pattern as an animal moves through an environment. Other cell types, such as head-direction cells, provide information about the animal’s directional orientation, and border cells activate when an animal is near environmental boundaries. The lateral entorhinal cortex (LEC) primarily supports the processing of time and episodic memory formation. These cellular mechanisms allow the entorhinal cortex to generate a spatial metric and contribute to the formation of declarative memories, which include conscious recollections of facts and events.
Significance in Disease Progression
The entorhinal cortex is notably vulnerable in certain neurological conditions, particularly Alzheimer’s disease. It is often one of the first brain regions to show pathological changes, making it a focus for early detection research. Abnormal protein aggregates, specifically neurofibrillary tangles (composed of tau protein) and amyloid plaques, frequently begin accumulating in the entorhinal cortex.
Tau tangle formation starts early in the entorhinal cortex before spreading to other brain areas like the hippocampus. This early pathology often leads to the initial memory and navigational deficits observed in Alzheimer’s patients, such as disorientation and difficulty forming new memories. The dysfunction of entorhinal cortex activity, rather than just cell death, is thought to contribute to these early symptoms.