A brainless slime mold uses a form of spatial memory to navigate complex environments in a manner similar to that used by autonomous mobile robots, a study reports. Slime mold uses an externalized spatial “memory” to navigate in complex environments is published in PNAS.
Chris R. Reid and colleagues tested the slime mold Physarum polycephalum for the presence of spatial memory systems, which had not been previously reported in organisms lacking a central nervous system. Physarum leaves behind a thick mat of translucent slime as it moves, and the researchers hypothesized that Physarum used this extracellular slime as an externalized spatial memory system to recognize and avoid areas it had already explored.
The authors challenged the slime mold with a U-shaped trap problem, a common test of autonomous navigation in robots, which required the slime to reach a chemoattractive food goal behind a U-shaped barrier. When Physarum could use the extracellular slime to determine where it had been before, it reached the food far more often and took significantly less time to do so than when it could not use the extracellular slime. Slime molds that were unable to use their externalized spatial memory spent almost 10 times as much time travelling over areas that they had previously explored. Externalized spatial memory greatly improves Physarum’s ability to navigate complex environments, and may have been a first step in the evolution of memory in higher organisms, according to the authors.