Action Potential

Teaching an old organism new tricks

How many neurons are required for learning and memory? None, according to Saigusa et al., who report basic learning behavior in unicellular amoebae in a recent article in Physical Review Letters.

The amoeba Physarum polycephalum is sensitive to environmental conditions. At room temperature, Physarum move at a constant rate. However, dry air slows the rate of Physarum movement.

The authors puffed dry air on Physarum once an hour for three hours. On the fourth hour, Physarum slowed down, even when no puff of air was delivered. Subsequent hours without air puffs slowly extinguished the periodic slowing of Physarum movement. However, one dry air puff six hours later reactivated the hourly behavior pattern.

These behaviors are consistent with rudimentary learning in higher organisms. Do these data indicate that unicellular organisms can learn? Physarum, like other organisms, have precise biological rhythms set by cellular oscillators. So, Physarum may be particularly sensitive to events occuring at regular intervals, and their periodic slow-down may represent the setting of a biological rhythm. However, rhythms alone do not explain extinction of the behavior in the absence of additional dry air puffs.

Do these data indicate a potential origin for learning, or do they indicate that our definition of learning in complex organisms is too simplistic? I’m a bit torn.


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    Curtis said:

    This is an interesting study. So Physarum learned to regulate its behavior patterns based on puffs of air? Did the article state how many times this was conducted or any possible confounding factors that may have affected the outcome of the study? Overall, I think it is very interesting and would like to lean towards it indicating that our definition of learning in complex organisms is too simplistic!

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    Aaron said:

    Yes, nice and interesting example…

    I wonder what you guys think how these kinds of learning processes work. What does science say? Are there any of you into morphogenetic field research (Rupert Sheldrake)? Do you think the “conciousness” of a monad is stored both inside and outside the material dimension? Obviously perception and learning do not exclusively work through neuron cells…