The cerebral cortex is one of the best known, developed and visible structures of our brain, possessing a great amount of functions that allow us to be who and how we are and to behave in an adaptive way in order to survive. But we are not facing a homogeneous mass that takes care of everything: different brain regions have different nerve fibers that specialize in different functions.
While it is common to know names such as prefrontal cortex or orbitofrontal, other areas are not as popular and often go unnoticed despite performing important functions. Among the latter we can find the entorhinal cortex , which we will discuss in this article.
What is entorhinal cortex?
The entorhinal cortex is a region of the brain located in the ventromedial temporal region, specifically located in the parahippocampal gyrus in a caudal fashion to the olfactory cortex of uncus and in direct contact with the hippocampus. It includes the areas of Brodmann 28 and 34, and borders on the perirrinal cortex and lateral groove.
This brain region has multiple connections to different areas of the brain. It connects with the olfactory and visual pathways and with different structures of the temporal, parietal and frontal lobes (including the orbitofrontal cortex. However, the structure with which it has the highest level of connection is the hippocampus, serving as a relay centre that distributes the information that enters or leaves it and acting as a bridge between it and other areas of the brain. The link between the hippocampus and the entorhinal cortex is carried out through the so-called perforating pathway.
It is considered an area of association that finishes integrating and sending the information to the hippocampus, as well as a relevant part of the limbic system, receiving afferences from the amygdala and contributing to endow the sensory information with emotional components in the memory.
The entorhinal cortex plays a very important role in our organism, allowing the realization, integration and good functioning of a great number of cognitive functions . Some of the functions in which this part of the cortex has been most involved are the following.
1. Relay centre
Traditionally its most well-known function, one of the multiple roles of the entorhinal cortex is to allow information from the rest of the cortex to reach the hippocampus and in turn allow information from the hippocampus to reach the rest of the brain.
2. Memory: formation and consolidation of memories
The entorhinal cortex is considered one of the most relevant brain nuclei in terms of memory capacity, being the bridge through which information arrives and is sent to or from the hippocampus.
This is a fundamental region in the formation and consolidation of memories , in fact, the lesion of the entorhinal cortex can make it difficult or even impossible to encode and record new content or information, producing antegrade amnesia.
One aspect to note is that this cortex is active during sleep, especially in REM, something linked to its role in consolidating memories in the memory.
The entorhinal cortex is not only important in the formation of memories, but also in the recognition of stimuli . This is because it is deeply linked to semantic memory, which dictates to us what the things we see are and allows us to recognize them.
4. Association of visual and auditory information
This brain region also plays an important role at the associative level, being an area where auditory and visual information are integrated. In fact, through the entorhinal cortex passes information referring to all the senses, although this information comes directly from areas of multimodal association (that is to say, that not only does the information of one sense arrive, but directly the integration of several).
5. Space Navigation
Another function in which the involvement of the entorhinal cortex was observed is in orientation and spatial navigation. This area is the one that allows us to know in which direction we are moving , being involved in the formation of mind maps.
6. Odour coding
The entorhinal cortex also plays an important role with regard to the olfactory system. Specifically, has been associated with the capacity to encode the intensity of the odour and in the association of odours with memories.
Some associated disorders
The entorhinal cortex is an important brain region whose injury can have multiple consequences and effects. Mainly, alterations in memory and recognition are produced, but difficulties also appear at the level of orientation, visual and motor problems.
Some of the main disorders in which lesions in the entorhinal cortex have been seen (usually in conjunction with those of the hippocampus) include the following.
1. Amnesic syndrome
Amnesic syndrome is understood to be that alteration of memory derived from some type of brain injury (psychogenic amnesias or those produced by non-organic mental alterations are not included in the syndrome).
In amnesia syndrome there is basically an anterograde amnesia in which the subject is not able to record new information, which may or may not be accompanied by retrograde amnesia (no memory of previous events in the subject’s life). Traditionally linked to hippocampal problems, in this type of syndromes there is also a significant involvement of the entorhinal and perirhinal cortex.
Multiple authors and researchers consider that the entorhinal cortex is one of the points where Alzheimer’s originates, being one of the first areas affected by this disease. Specifically, neurodegeneration is observed generated by the accumulation of tau protein in the lateral part of the entorhinal cortex, as well as the formation of beta-amyloid plaques. This will later expand along the temporal cortex and finally to the rest of the brain as the disease progresses.
While this is not a disorder per se but rather a symptom, agnosia is understood as the lack of recognition of the properties of a stimulus with which we are familiar. The presence of lesions in the entorhinal cortex can hinder this process, as it is linked to hippocampal memory. For example, smell recognition may disappear.
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