Entorhinal Cortex

Entorhinal Cortex: Memories of Time

The brain is such a vast network of neurons all communicating in a precise synchronized order. How does it all work and what parts of the brain do what? In an effort to understand the brain and its functions each part of its anatomy must be explored. By focusing in on various parts of the brain and running extensive experiments we are able to dissect the complexity of how we function. In this exploratory paper over the brain a comprehensive look at the specialized brain area known as the entorhinal cortex (EC) will be covered. This comprehensive look will contain aspects of location in the brain, the size and anatomy of the EC, the main purpose and function of the area, how it communicates with the other parts of the brain, and its role in neurological disorder development.

Residing in the mediotemporal lobe is the entorhinal cortex. In terms of anatomical references, it would be on the ventral side of the brain, that extends dorsolaterally. It is comprised of two main areas, the medial and lateral entorhinal regions. These two regions of the EC are responsible for different aspects of sensory and signaling capabilities, which will be discussed later in more detail. 5 known layers comprise the EC, these too are specialized for certain input and output capabilities.

When taking a deeper look into the entorhinal cortex and breaking down its functions by region and layer we begin to see the comprised function of the structure. First, we will break the EC by its two major regions the lateral and medial. Research shows “a fundamental dissociation between the information conveyed to the hippocampus by its major input streams, with spatial information represented by the medial and non-spatial information represented by the lateral entorhinal cortex.” (Hargreaves, E.L. 2005). However, both are known to deal with memory attributions by way of hippocampal communications. It is said that the entorhinal cortex deals especially with memories during sleep. Now we will dissect the entorhinal cortex by layers. The EC layers most talked about are the superficial ones 1 and 3 and the deep layer 5.

All the parts of the EC form together to create an area of the brain that deals with memory via hippocampal and denate guyrus communication as well as spatial orientation via input form multiple areas of the brain. Though, it has been shown that more areas of the brain communicate to the EC. One study showed that “EC path cells, which varied their firing rate according to whether the patient was driving in a clockwise or counterclockwise direction, regardless of location. During navigation, path cells encoded directional attributes of the current context and may be an important input to unidirectional hippocampal place cells”(Jacobs, J. 2010).

In order to communicate with the hioppocampus about the memories it is retaining, like all brain areas it must talk through chemical communication via a neurotransmitter. The main neurotransmitter used in communication with the hippocampus by the EC is Glutamate. Having this as the neurotransmitter validates the entorhinal cortex having relation to memory components. In addition though studies have show that “Cholinergic projections to theentorhinalcortex(EC) mediate distinct cognitive processes through muscarinic acetylcholine receptors (mAChRs)” (Barak, S. 2010).

Now that there is a basic understanding of what the EC is and its function, we will take a look at what happens when that function is tampered with. The entorhinal cortex of the brain has been researched on and it has been discovered as problemiatic concerning certain neurological disorders. These disorders include: Alzheimers, depression, schizophrenia, and neurotoxicity. A brief exploration into each of these disorders will be given, beginning with Alzheimer's. This neurological condition is characterized by plaque deposits forming in the brain tissue. While the entorhinal cortex is not the primary site of this deposition, it has been seen to occur in this region eventually causing reduction. According to psych-it.com “These reductions in the entorhinal cortex might explain some of the deficits in memory consolidation, short term retention, and other cognitive functions in Alzheimer's disease and mild cognitive impairment”. Next, is depression a decrease in the size of the EC has been seen in cases of older patients who suffered from depression. In the case of schizophrenia it has been seen that prior to the other area of the brain to be affected, including the amygdale, the EC shows signs of decay first. Lastly, for the diseases is neurotoxicity. This is just simply displayed by showing signs of damage to the neurons within the entorhinal cortex due to an increased amount of stress. So by looking at the few diseases listed above there can be illnesses brought on by abnormal deposits, degradation of the area, or by stress causing an increase in glutamate transmission.

This area of the brain while commonly not known is quite an interesting and influential character. Being so small yet having such a large control over the proper functioning of memory recall. Edmond Burke once said, “Those who don't know history are doomed to repeat it”. Without this vital communication through the entorhinal cortex, such recollection of memories might be hindered or even lost. By understanding how this area of the brain works with others and the affect it has on disorders may someday be key in discovering how to stop the chain of events of such devastating diseases.

References

Barak, S., & Weiner, I. (2010). Differential Role of Muscarinic Transmission within the Entorhinal Cortex and Basolateral Amygdala in the Processing of Irrelevant

Stimuli.Neuropsychopharmacology,35(5), 1073-1082. doi:10.1038/npp.2009.210.

Hargreaves, E. L., et al. (2005) Major Dissociation Between Medial and Lateral Entorhinal Input to Dorsal Hippocampus. Science, 308. DOI: 10.1126/science.1110449

Jacobs, J., et al. (2010). A sense of direction in human entorhinal cortex. Proceedings of the National Academy of Sciences of the United States of America, 107(14), 6487-6492.

Moss, S. (2008). Entorhinal cortex. Retrieved from http:// www.psych-it.com

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