Someone who falls ill often finds it more difficult to learn than when they are in good health. We all know this from our own experience. The body seems to give priority to using its resources to fighting the illness instead of carrying out intellectual activities. This phenomenon naturally interests scientists and it has given rise to entirely new research areas focussing on the connection between the immune system and the nervous system. This summer ETH appointed a professor of psychology and behavioural immune biology.

This new research is not devoted exclusively to human beings, but is also directed at other vertebrates. There are ever more indications that infection by parasites impairs the learning capabilities of animals. It is not only vertebrates, however, who are capable of learning. As long as 90 years ago, Karl von Frisch used the phenomenal learning capabilities of these insects to prove that their bee dance is a way to communicate the existence of profitable food sources. Does illness also influence their learning capabilities? The question has remained unanswered until now. The evolutionary biologist, Paul Schmid-Hempel (1) and his research team have now given a positive answer to this question in a new study, published in the "Proceedings of the Royal Society of London" (2).

Proboscis demonstrates learning success

For their study the researchers examined bees, although not their well-researched dance. Instead, they analysed the insects' behaviour in a classical conditioning experiment. To begin with, the bees' antennae were sprinkled with sugared water, an unconditioned stimulus, which caused them to unroll their proboscis. As a reward the bees then received the sugary solution. If the bees were confronted with a citrus like odour, they reacted after a single "lesson" by unrolling their probocis. This behavioural pattern can therefore be used very well to quantify learning capability by the means of association.

Bees with active immune systems have more trouble learning. (Picture: P. Schmid-Hempel)

An immune response to forgetting

How do bees behave in this conditioning experiment if their immune system is activated? This is precisely the question investigated by Paul Schmid-Hempel and his colleagues. The bees were injected with a substance that triggered a strong immune response, but did not harm them. It transpired that when confronted with a citrus odour those bees whose immune system had been activated moved their proboscis for the duration of one minute – as strongly as the control group whose immune system had not been activated – but significantly less after twelve minutes. This indicates that the immune system requires a certain amount of resources, so a short-term, but no long-term, "memory" can develop if it is active.

Is it the octopamines?

In the study the reasearchers set up the hypothesis that octopamines, on which the associative learning of honey bees depends, might not be available in adequate amounts to build memory if a strong immune response was active. Schmid-Hempel points out that colleagues in Würzburg, who participated in this study, will continue to investigate the role of octopamines in the lowering of learning capability through immune response. Even should they fail to find anything here, the described behavioural study shows that the immune system of bees cannot be activated without significant loss of learning capabilities. It is easy to see that this could have possible far-reaching consequences. A hive of bees, whose members can no longer learn how to interpret the workers' dance, would certainly run into big trouble.