Transplanted human brain cells in a mouse brain provide insight into neural circuit formation
The experimenters used mice, kept in a conditioning chamber with a range of environmental cues while a small electrical shock was given to the foot of each mouse. The researchers found that the mice rapidly learned to fear the specific environment associated with the previous shock. After just one exposure the mouse froze when it was put back in that environment, even when no shock was given. The scientists think this is an expression of the fear they remember in association with that environment.
These mice were now replaced with others who had been genetically modified so that they could not produce myelin. These mice also learned to fear the specific environment with one learning experience based on fear. They froze when exposed to that cue in the chamber even when no shock was experienced. However, their memories faded away quickly. In other words, without myelin formation, fear-based memories don’t consolidate and become permanent. These mice were also found to have long-lasting alterations to neural activity in the prefrontal cortex.
The present study adds to the existing evidence that myelin formation is essential to strengthening and maintaining these new connections so that the memory becomes persistent. In other words, myelin not only helps form and execute physical movements but in the establishment of durable memories.
How does myelin act to do this? It may be that its ability to enhance signal speed and efficiency of conduction along the axons helps to change the way important nerve signals travel along the major nerve networks.
Researcher Simon Pan comments, “This study is a significant advance in our understanding of how the brain remodels itself in response to a learning experience. A cardinal property of myelin is its stability, which uniquely positions it to support enduring, even life-long, memories in humans, mice, and other animals.” Implications
Finding the exact role played by this substance in learning will help uncover the way learning is carried out, how memories are formed, and how mood and anxiety disorders can be treated and identified using these discoveries.
For instance, an earlier study found that, capitalizing on earlier research by Jonah Chan who is also involved in the current study, the antihistamine drug clemastine fumarate which could be useful in the treatment of multiple sclerosis could be used to establish even more lasting conditioned fear-induced memory in mice.
When veterans with PTSD underwent MRI of their brains, the hippocampal region of the brain seemed to have a higher than average myelin content. This is interesting because memory consolidation to transform them from short- to long-term memory occurs in this area.
The question is, could myelination be part of the reason, at least, for the abnormal function of memory in PTSD? Says Mazen Kheirbek, “Myelin plasticity could be beneficial for skilled learning such as playing a piano or remembering locations, but also detrimental if it leads to persistent, overgeneralized fear responses to everyday situations.”
Chan sums up, “We are now seeing that the process of oligodendrocyte generation and myelination can be quite dynamic in the normal adult brain. It's a form of plasticity that responds to experience and that causes long-lasting changes. This is a very recent concept that we are in the early days of exploring.” Journal reference:
Pan, S., Mayoral, S.R., Choi, H.S. et al. Preservation of a remote fear memory requires new myelin formation. Nat Neurosci (2020). https://doi.org/10.1038/s41593-019-0582-1
Also in Industry News
How to decide whether or not to start treatment for prostate cancer?
Analysis of the SARS-CoV-2 proteome via visual tools
$65m investment increases British Patient Capital’s exposure to life sciences and health technology