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One of the early brains??

I recently saw this article, written by Carl Zimmer, who writes a blog called The Loom. This was about Slime Molds. These are organisms that appear to be similar to fungi. But as is mentioned in another article, they are different from Plants, Animals, bacteria and fungi. The articles themselves are very interesting and worth a read, but I wanted to share with you an interesting piece of research done on these organisms.

One type of Slime Molds is the Physarum Polycephalum. After reading the articles, and doing more googling, I learnt that these organisms are regularly used in classrooms because they are easy to study. This Physarum, is actually one single cell. As we were told in our biology class, a cell has a nucleus. But the Physarum, has many nuclei, inside its one cell. It is in essence many cells, but without cell boundaries. At the beginning of its life there will be only one nucleus inside the cell. Thereafter, it continuously reproduces, and keeps adding nuclei and thereby grows.

Physarum Polycephalum. Pic by Jerry Kirkhart(http://flickr.com/people/33466410@N00)

They are simple organisms, and so when we see one, we would not give it much respect. But would you believe that they have what could have been the precursors of  a brain. These organisms are known to solve puzzles, conquer mazes and so on. But today, we will see its capacity to remember and recollect. If you think that is not surprising, remember that it is just a single cell, without a brain or any advanced organs. The fact that have a rudimentary form of memory was discovered by some researchers in Japan. Wanting to see what they had done, I looked at the original paper they published.

Physarum prefers humid and dark areas for it to grow. So these researchers put it on a plate, and directed its growth onto a narrow lane, so that they could accurately measures its growth. They did at a temperature of 26 degrees and a humidity of 90%. These were the conditions for an hour, after which, for a brief period of 10 minutes, they reduced the temperature to 23 degrees and humidity to 60%. During these 10 minutes, they noticed that the growth of the organism had slowed down. Once the 10 minutes were over, they reverted the temperature and humidity to the original values of 26 degrees and 90% and consequently the organism too resumed its normal growth rate. After the second hour, they again changed the environment for 10 minutes and brought it back to the original values. They repeated this a third time. And all three times, the growth went down during those 10 minute intervals.

What happened next was what is surprising. At the end of the fourth hour, when the temperature and humidity should have been reduced a fourth time, the scientists did nothing. They just continued with the environment as it was. But the physarum, anticipating another 10 minute period of unfavourable environment, reduced its growth, even though the environment did not change. Think of that!! How could a single celled organism, measure the duration, remember it and anticipate a change in environment?

Not just that. After the initial three stimulations, the scientists kept quiet for 5 hours. At this stage, the physarum stopped anticipating the hourly change and continued to grow as usual even at the end of an hour. But at the end of the 8th hour, by which time the physarum had apparently forgotten the whole thing, the scientists again changed the environment. Now the physarum, with its previous experience, started anticipated this change in the 9th hour, when the scientists again stayed away from doing anything. This also showed that they could recall what they learnt previously, since with just one intervention in the 8th hour, there was no information that the scientists will again intervene after another hour. They could have got this information only from past experience.

Time What the scientists did How the Physarum reacted
End of hour 1 Change environment Reduced Growth
End of hour 2 Change environment Reduced Growth
End of hour 3 Change environment Reduced Growth
End of hour 4 Nothing Anticipatory reduction of growth
End of hour 5 Nothing Anticipatory reduction of growth
End of hour 6 Nothing Normal Growth
End of hour 7 Nothing Normal Growth
End of hour 8 Change environment Reduced Growth
End of hour 9 Nothing Anticipatory reduction of growth

This clearly shows, that they could recall what they had previously stored. But, they do not have any sort of brains the way we have. There is some speculation in the paper as to how such periodicity could exist in the cell. But, whatever the cause is, it is the result of a very basic chemistry that happens in their cells. We do not know how they do it.

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