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Irrational Decisions

Do you believe you are able to decide rationally? We always think we are in control of our choices, but often our subconscious mind cheats us. Imagine you travel to a foreign city. There you would want to go out for dinner and choose the restaurant rationally by studying menus, prices and ambience. But because you wanted to see so many things, the sightseeing finishes late in the evening and you are hungry and tired. So you might end up picking the first restaurant you can find, regardless of whether it looks dodgy, charges fantasy prices and even serves food you don’t like.

Professor Ray Dolan from University College, London tried to give a neuroscientific explanation for this phenomenon during the Edinburgh International Science Festival in the spring. In his words, ”the human mind is a Parliament and not the Executive”. The human mind has different feedback mechanisms that allow it to judge the environment and decide between several options. The final decision is not made by an executive (your brain) alone. As in a parliament many types of decision-making contribute to the final result.

To grasp this idea, we first have to understand the process of decision-making. Scientists divide decisions into three categories: goal orientated decisions, such as the decision to go on a diet in order to fit into those old trousers again, aim for a long term profit; habitual decisions can result, for example, in choosing an Italian restaurant, simply because you always do; and Pavlovian decisions, which may result in short term benefits, and are made through a process that behavioural scientists call ‘conditioning’. This is the learned association of a stimulus with a feeling; for example your watch indicating lunch time can make you feel hungry. When these categories of goals conflict, we may end up making a seemingly irrational decision.

But to err is not only human. Tanya Latty and Madeleine Beekman from the University of Sydney chose a very curious research subject to investigate irrational decisions: the slime mould Physarum polycephalum. Although its name translates into ‘many-headed slime’, it is not a single organism but thousands of cells that can merge into one yellowish mega-cell, which behaves like one creature. Completely brainless, it does not seem a good subject for studying decision-making. However, the reason the scientists chose it was to determine whether irrationality is caused by an animal’s brain or is a basic feature of all organisms.

Since slime moulds are not very fussy about food, the two scientists only had to offer them a choice of oats in varying concentrations. They gave the option of a very thin porridge-like meal containing only 5% oats or a thicker one containing twice the amount of oats.  To make the decision more difficult they placed the food either in light or darkness; the mould prefers darkness because it dries out in light.

They found that the slime mould usually seemed to decide rationally. When fed well, it would avoid eating the 10% oatmeal that was exposed to light and instead chose the thinner oatmeal in darkness. This is a rational comparative balance between food quality and safety. The slime mould prefers to eat less rather than to risk drying out. When P. polycephalum was starved before the experiment it chose the 10% oatmeal regardless of the amount of light, again suggesting a rational decision. The mould would risk drying out to get the food it needed to survive.

However, in some cases the decision seemed irrational. When starved and offered oats in  concentrations of 3% or 5%, both in light, it did not show a preference, although when fed well it chose the thicker oats if it had no choice between light and darkness. The better food would have allowed it to grow twice as much, a clear advantage.

This suggests that the slime moulds, in Pavlovian mode, were hindered from making a rational decision. The situation is comparable with the random choice of a restaurant when you are very hungry. The mould just chose any food without considering its quality. The irrationality could have come from it having many nuclei within its mega-cell. Contradicting stimuli from the many nuclei could cause conflict. Nevertheless, like us, this brainless ‘primitive’ organism is able to make comparative decisions. 

In our apparently rational world, it is unthinkable that we might not always be in control of our decisions. But despite our sophisticated brains we face the same challenges as the simple slime mould. So perhaps it is a good idea after all to choose the next restaurant by going with your gut feeling.

Thilo Reich is an undergraduate in infectious diseases


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