Roundworms have a short memory, so they forget new information within 2 to 3 hours after learning it. However, new research shows that if you leave it on ice, it won’t be forgotten until it returns to room temperature. This is what the scientific journal Nature reported on the 22nd (local time) based on a paper by researchers at Tel Aviv University in Israel published on bioRxiv, a pre-release site for biology papers.
To confirm this, Tel Aviv University geneticist Professor Oded Rechavi’s research team conducted an experiment on Caenorhabditis elegans, a cousin of the roundworm, as a laboratory worker. The researchers starved the Caenorhabditis elegans worms and made them smell a certain smell that the worms usually like, causing them to dislike that smell. However, because the memory is short, after two hours, C. elegans forgets the negative association and becomes attracted to the smell again.
Dana Landschaft Berliner, a member of the research team who was a graduate student at the time, placed the bugs on ice and discovered that they retained smell-related memories for at least 16 hours. However, as soon as I took the ice away, my ‘memory clock’ started working again and I forgot my dislike of the smell within 3 hours.
Berliner identified several ways to influence memory in C. elegans. If left in a cold place overnight before receiving memory training, even if placed on ice, they quickly forgot the smell as usual. He also found that when administered lithium, memories were retained longer even at room temperature.
The core of this reaction may be a signaling molecule called diacylglycerol. Diacylglycerol is known to regulate cellular processes related to memory and learning and is essential for odor-related learning.
The researchers found that memory retention was associated with decreased diacylglycerol levels in both ice and lithium treatments. The researchers called the diacylglycerol cycle the ‘forgetting switch’ because it is involved in delaying memory loss.
Lithium is known to inhibit enzymes that make diacylglycerol precursors. This explains the association between low diacylglycerol levels and lithium. This is thought to underlie the effects of lithium on patients with bipolar disorder, Professor Rechavi explained.
The researchers also found that memory retention was linked to the hardening of cell membranes due to cold. Two strains of Caenorhabditis elegans with abnormally hard cell membranes had a slower forgetting rate than normal nematodes, even at room temperature. Experimental results showed that physical hardening of cell membranes delays forgetting.
This study reveals the mystery of how memories are created and destroyed. It also raises the question of why the acuity of insects’ memories varies depending on environmental conditions. Professor Rechavi asked, “Bugs are perfectly capable of retaining memories for a long time, so why do they forget?” “Is it because you are optimizing something? Perhaps there is a reason why we hold on to memories for certain periods of time.” Does this trade-off occur in other animals?
Professor Rechavi’s team is currently investigating whether similar memory phenomena occur in other organisms that survive cold temperatures, such as tiny tardigrades known as water bears and certain types of turtles. “Those laggards will keep us busy for a long time,” Professor Rechavi said.
The paper can be found at the following link (https://doi.org/10.1101/2024.04.03.587909).
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