Most of our memories fade in a few days or a week while some of them stay for even months and years or sometimes for good. There are a few experiences in our lives that tend to leave some long-lasting imprints in our minds and neural circuits. This is also a question that which factors make this memory to persist?
In fact, this is an old question in the field of neurobiology, which has not been solved yet, but a few new pieces of research and evidence have provided surprisingly new solutions to this question.
On February 10th, 2020, a study was published in the journal of Nature Neuroscience, San Francisco, in which scientists discovered that learning on account of “fearful responses” was quicker in mice. But in order to gain this response and to make it long-lasting, cells in our brain need to increase the amount of certain insulating material in nerves referred to as Myelin.
Myelin tends to stabilize and reinforce the newly generated connections in our nervous system. Although the duration and processes of short-term learning are quick but to change it into long-term memory, brain cells need this fatty material.
According to these researchers, a continued effort and research on myelin role in the nervous system will help us to deal with problems associated with PTSD (post-traumatic stress disorder). PTSD patients tend to have intrusive and unwanted memories, which are continuously reprocessed because these memories are strongly coded inside our brain cells.
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What is myelin?
Myelin is a smooth, white, and fatty substance which tends to cover our nerve fibers or axons. Myelin is made up of some specialized cells in the brain known as oligodendrocytes. These brain cells wrap the fibers of the nerves originating from cells. If this wrapping continues and repeats, then a thick covering is created around nerves made up of fat and proteins.
Myelin is known for its insulating role, which forms a sheath over the nerve fiber. This sheath is some times interrupted with some bare spots referred to as Nodes of Ranvier. These nodes allow the impulses of nerves to travel from node-to-node or in a series, instead of continuously traveling along the nerve fiber length. This phenomenon helps to increase the impulse traveling speed.
The function of myelin:
The function of the myelin sheath is very crucial in nerve conduction and impulses traveling. Information networking in the brain functions with the traveling of impulses to and from the source. In these areas of the brain, high-speed neurons (axons) can stretch to even three feet or more, which makes a long nerve pathway.
With the formation of these long neuronal pathways, the ability of the brain to quickly respond to even the slightest information or command to move a specific body part or muscle group, increases.
In neurology, several neurological diseases occur due to the destruction of this myelin sheath. In MS (multiple sclerosis), which is a progressive muscular degenerative disease, myelin loss, and the damage is the main culprit, which results in loss of functions and muscle control.
When is myelin formed?
According to some important researches, myelin is produced inside the brain when we make some long-term memories or specifically when an individual tends to learn some complex movement of muscles like that in roller-skating. This medical discovery is a very crucial and important addition to the fact that neuronal connections are formed when some process of long-term memory takes place.
According to the well-renowned scientist and member of UCSF, Weill Institute for Neurosciences, a brief and single experience of fear-learning can lead to some long-term modifications in myelination of nerves and other neurophysiological changes associated with it inside the brain. These changes can even be detected after a month.
How was the study performed?
The scientists used a few mice that were kept in a specific chamber having a range of cues with small electric shock given to their feet individually. The researchers observed that these mice were more rapidly learning the subject in a fearful environment as with the shocks.
They put one mouse in shock and removed it after a while. After some time, the same mouse was placed in that environment, but no shock was given, and still, the mouse was frozen. This experiment proved that fearful experiences are associated with memories of the specific environment.
In the second part of the study, scientists replaced the experiment with some mice who were modified not to produce myelin genetically. When the same experiment was performed on these mice, they froze for one time when no shock was applied, but their memory of this event faded quite quickly. This experiment proved that without the formation of myelin, even the fearful memories can’t stay permanent and consolidate. These modified mice were found to have some alterations in their neural activities as well.
How will this study be beneficial?
This study can help in finding the exact role of the myelin sheath in learning and the formation of memories.
For instance, patients with PTSD, MRI of their brains showed that the hippocampus region in their brain was having more than enough myelin content. This was an interesting event as it showed that most of the memory transformation from short-term duration to long-term duration occurs in this part.
This study can help treat patients with PTSD and other related neuropsychological disorders. Other than it, this discovery can help create a strong foundation for learning quickly and persisting it for the long-termed duration.
The human brain is a complex organ. A number of neuronal connections are present in the brain. Nerve fibers are often insulated or covered by some fatty and thick material known as the myelin sheath, which helps in an increase of conduction speed in the brain. Other than it, a recent study proved that some fear-based learning can help in the plasticity of myelin in brain cells, which can change the short-term memories into long-term memories. This study won’t only help strengthen human memory but will also provide treatment to patients suffering from memory-related problems as PTSD.