How the Brainless Slime Mold Stores Memories

New research finds the organism can remember the location of food by altering the diameter of the creeping tendrils it uses to explore its surroundings

Slime mold
Slime mold in a petri dish. New research finds that slime molds can store memories by changing the diameter of the branching tubes they use to explore their environment, allowing them to keep track of food sources. Nico Schramma / MPI-DS / TUM

Slime molds, which are not actually fungi but cousins of single-celled amoebas, are goopy organisms that can find their way through a maze and remember the location of food—all without the benefit of a brain or nervous system. Now, new research brings us a step closer to understanding how exactly these slimy blobs store the “memories” that allow them to do things like relocate food, reports Nicoletta Lanese for Live Science.

When placed in a new environment, a slime mold sends out a fractal net of oozing tendrils to explore its surroundings. According to the new research, published this week in the journal Proceedings of the National Academy of Sciences, the slime mold encodes information about what it finds during these searches by changing the diameter of its exploratory tubes.

"There is previous work that biological signals within slime molds can store information about previous experiences," Karen Alim, a biological physicist at the Technical University of Munich and co-author of the study tells Tara Yarlagadda of Inverse. "Yet, that the network architecture can store memories is [a] novel concept in the context of slime mold and fungi."

The study’s main finding emerged from simply watching a bright yellow slime mold named Physarum polycephalum do its thing under a microscope. When the slime mold found food, the researchers noticed the network of tubes and tendrils changed its architecture in response, with some getting thicker and others getting thinner. What’s more, that pattern persisted long after the slime mold finished its meal.

“Given P. polycephalum's highly dynamic network reorganization, the persistence of this imprint sparked the idea that the network architecture itself could serve as memory of the past“, says Alim in a statement.

By measuring the changing diameters of the slime mold’s tubes when it found food and by developing a computer simulation of the organism’s behavior, the researchers found that the tubes closest to a morsel of food got thicker while those farther away withered and sometimes disappeared entirely, according to Inverse.

That pattern of thicker and thinner tubes ends up serving as a persistent imprint, that is, a rudimentary form of memory.

Per the paper, “memories stored in the hierarchy of tube diameters, and particularly in the location of thick tubes, are subsequently layered on top of each other, with every new stimulus differentially reinforcing and weakening existing thick tubes in superposition of existing memories."

Given their observations, the researchers think that when the slime mold detects food it releases some chemical that softens the walls of nearby tubes, allowing them to expand. However, Alim tells Live Science that their results give no clues as to what chemical this might be, adding that this will be the subject of future studies.

“These results present an important piece of the puzzle in understanding the behavior of this ancient organism and at the same time points to universal principles underlying behavior,” says Alim in the statement. “We envision potential applications of our findings in designing smart materials and building soft robots that navigate through complex environments.”