Is there a left-right difference in the function of the hippocampus, which controls memory?


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left-right difference in the function of the hippocampus

There are a pair of hippocampi on the left and right sides of the limbic system that control memory. The left and right hippocampus do not appear to have any difference in size, shape, or basic structure. However, as laterality of the brain is being debated, it is thought that there is also laterality in the function of the hippocampus, which has become an interesting research theme in recent brain science. We will explain the left-right difference of the hippocampus and the functions of each in an easy-to-understand manner.

Is there a difference between the left and right hippocampus?

The hippocampus , which resembles a seahorse and is part of the limbic system, is located deep in the left and right temporal lobes. There is a pair in And there doesn’t seem to be any difference in the size, shape, or basic structure of the left and right hippocampus. They also have the same basic role of memory.

However, as the left-right difference of the brain has been discussed, it has been thought that there may be a slight difference between the left and right hippocampus, which has become an interesting research topic in recent brain science. In this article, I would like to introduce some of the findings on the laterality of the hippocampus and the functions of each.

Read Also: What happens if you cut the corpus callosum? Right brain and left brain thinking from “separate brain”

What happens if you lose either hippocampus? Differences in function considered from the aftereffects of surgery

The first is the knowledge that there is a left-right difference as an effect of excision of the hippocampus.

If the hippocampus is thought to be abnormal due to a disease called epilepsy, the hippocampus may be surgically removed for treatment. In particular, in medial temporal lobe epilepsy with hippocampal sclerosis (a condition in which the hippocampus is atrophied and degenerated), if the lesion is only on either the left or right side, approximately 80% can be reduced by resecting the medial temporal lobe structure including the hippocampus. Since it is said that seizures disappear in cases of , surgical treatment is still often selected.

The hippocampus plays a necessary role in making memories, so memory impairment occurs after hippocampal resection, but the postoperative impairment is greater when the left hippocampus is resected than the right. It seems that. As introduced in “

Should I talk to my lover from the left side? Is there a scientific basis for stories related to the right and left hemispheres? ” is primarily responsible for language-related memories. Therefore, it is thought that the loss of the left hippocampus would have a greater impact on us humans, whose main means of communication is language.

In experiments using mice, differences between the left and right hippocampi at the micro level

In 2003, a research group from Kyushu University reported in the authoritative American journal “Science” that there was a difference in the amount of glutamate receptors in synapses in the hippocampus of mice. Science, 300(5621):990-994, 2003 ). The main excitatory neurotransmitter in the hippocampal neural circuit is glutamate, and there are several types of receptors that receive this information. There was a clear left-right difference in the distribution of Since this type of receptor is well known to be involved in memory formation in the hippocampus, it was thought that there might be differences in the mechanisms of memory formation in the left and right hippocampus.

In the same research group, Dr. Yoshiaki Shinohara (National Institute for Physiological Sciences, RIKEN) conducted further experiments and found that the shape and size of synapses differed between the left and right hippocampus ( Proc Natl Acad Sci USA, 105 (49 ): 19498-19503, 2008 ). We also found that differences in the shape and size of synapses are related to differences in the amount and type of glutamate receptors.

Is the right hippocampus susceptible to environmental influences? Differences in how the left and right hippocampus grow

Dr. Shinohara of RIKEN, who was interested in the laterality of the hippocampus, also reported in 2013 the experimental results that “the influence of the environment on the development of the hippocampus has laterality” ( Nature Communications, 4: 1652, 2013 ). Rats aged 3 to 6 weeks were divided into an “isolated group” where they were kept alone in a cage and a “enriched environment group” where they were group-reared in cages with playground equipment. By comparing EEG activity and synaptic density, they found that a rich environment increased EEG and synaptic density in the right hippocampus more than in the left. The right hippocampus may be more susceptible to environmental influences.

The difference between the left and right hippocampus is more than you can imagine! Nerve connections work well in balance

It seems that the hippocampus has more left-right differences than I had imagined. In particular, research data showing clear differences in the structure of synapses and the distribution of receptors at the micro level is very interesting. However, the findings presented above should be interpreted with caution.

First of all, all observations were made with mice and rats, so I don’t know if they apply to us humans.

In addition, we must not overlook the fact that the neural communication between the left and right hippocampus was cut off during the experiment. The left and right hippocampi are not independent, and are included in the “corpus callosum ” The left and right hippocampus communicate with each other through commissural fibers. The results are shown. By the way, it seems that there was no big difference in the distribution of synapses and receptors in the hippocampus in a natural state with proper neural communication between the left and right.

In other words, it would be correct to assume that the left and right hippocampi originally have different characteristics, but by communicating between the left and right hippocampus, they function in a well-balanced manner so that there is no difference.