Memory Without A Nervous System
Memory is a very complicated process that is still being researched to this day. The process of learning and retaining information is still not fully understood but it is universally associated with the nervous system. The nervous system is a body system that communicates information through electrochemical signals around the body and from the environment using nerves, your brain, and your spinal cord. However, what if there was an organism that has a memory, but not a nervous system? Slime molds are organisms made up of many nuclei in a shared cytoplasm enclosed in a membrane (1). You may have heard of slime molds before, when in the year 2000 a group of researchers placed slime molds into a maze and placed a nutrient source at the other end. The slime was able to grow through the maze and when it reached a dead end it would retract, allowing it to find the shortest possible pathway to the nutrients (2). This brings us to today where two researchers, Mirna Kramar and Karen Alim, discovered that despite the lack of nervous system, the slime mold was able to remember nutrient source locations (3). It was discovered that slimes have interconnected tubes that vary in length and diameter. When the slime contacts a nutrient source, it locally releases a chemical softening agent that alters tube length. Tubes that receive high intensity of this chemical grow in diameter which causes other tubes to contract and shrink. This leaves a permanent change in the slime that acts as a form of memory that mimics the idea of synaptic plasticity in humans. Synaptic plasticity is the idea that neurons form stronger connections when activated repeatedly, which helps your brain to form memories. Slimes undergo a similar process when a nutrient source is detected, the tubes grow or shrink making it easier for the slime to find the nutrients in the future. This discovery shows that our initial idea of what memory is may not be fully accurate, and that cellular organisms may have more complicated information processing than we originally thought.
References:
Brownell, L. (2021, July 15). Thinking without a brain. Wyss Institute. https://wyss.harvard.edu/news/thinking-without-a-brain/
Nakagaki, T., Yamada, H., & Ágota Tóth. (2000). Maze-solving by an amoeboid organism. Nature, 407(6803), 470–470. https://doi.org/10.1038/35035159
Kramar, M., & Alim, K. (2021). Encoding memory in tube diameter hierarchy of living flow network. Proceedings of the National Academy of Sciences of the United States of America, 118(10). https://doi.org/10.1073/pnas.2007815118