An investigation has discovered how unicellular organisms can store memory without having a nervous system: they absorb the experience, keep it as a memory and are able to pass it on to other colonies.
Physarum polycephalum is a slime mold known as the many-headed slime. It is found in shaded areas, fresh and humid, such as between leaf litter and decaying logs. It is usually yellow in color and feeds on spores of fungi, bacteria and other microbes. It is used as a model organism for studies of amoeboid circulation and cellular mobility.
One of its main characteristics is that it does not have a nervous system. However, research developed in 2016 discovered that it does store memory: it was able to remember an offensive substance, although unpleasant and at the same time pass that memory on to other fungi.
You may also like:
Now, new research developed by scientists of the CNRS of France and the University of Toulouse, directed by Paul Sabatier, has discovered how it is possible that without a nervous system this unicellular organism can learn something, remember it and transmit it. The results are published in Philosophical Transaction of the Royal Society B.
The explanation obtained is as follows: this fungus learns to tolerate an unpleasant substance by simply absorbing it.
They checked it by observation: It was already known that fungi exchange information only when their venous networks merge. The new study has also determined that the basis of its memory is the substrate of experience.
That is, the fungus perceives an unpleasant substance, absorbs it (to know it better) and that substance automatically becomes its own memory. At this very basic level of life, the nervous system, typical of more complex beings, is not necessary to create and store memory.
To reach this conclusion, the scientists developed the following experiment. First, for six days they used a colony of these fungi to salty environments. Next, they discovered that they had 10 times more salt concentration in their organisms than other colonies not exposed to salty environments.
Then they placed them in a neutral environment and observed that the fungi excreted the concentrated salt in only two days and lost their memory. They no longer remembered that salt was unpleasant. In this way, the researchers found that there was a link between the concentration of salt in the body and the “memory” of learning.
But the experiment did not end there. To confirm this hypothesis, the scientists introduced it another colony of fungi, which had not had the experience of a salty environment, the “memory” that the salt habitat colony had experienced.
Even in the latency state
And they observed that in two hours, the colonies that had not had experience with the salt behaved exactly like those that had been six days in the salt environment: they adapted the salt concentrations to the same levels.
They had assimilated the learning of the other colony, without having had their experience and without any contact with the first colony.
The researchers also found that after a month of entering latency, these mushrooms with built-in memory (not based on their own experience), retained the habit of having adapted to a salty environment.
That is, memory transmission can be performed even when the fungi enter the latency state, a frequent reaction in these organisms when environmental conditions deteriorate. These fungi had absorbed the salt despite being in a state of dormancy and retained this long-term memory.
The researchers conclude that the unpleasant substance (in this case salt) is the memory support that fungi show. Now they intend to discover if these unicellular organisms can memorize several unpleasant substances at the same time, and whether or not they can accustom themselves to more complex environments through this unique form of learning.
Memory inception and preservation in slime molds: the quest for a common mechanism. A. Boussard et al. Philosophical Transaction of the Royal Society B, 22 April 2019. DOI: https: //doi.org/10.1098/rstb.2018.0368