Which animal has no head?

The memory of animals

Anyone who wants to research memory has accepted a great challenge. Because the human brain consists of 100 billion nerve cells. Each one is in contact with 1000 others.

The brain has a lot to do: It has to process information from the environment, control language, behavior and movements, but also store, sort and remember. To do this, the scientists are studying the less complex brains of animals. Such as the larvae of zebrafish.

A small fish wants to be a school

At the Max Planck Institute in Frankfurt, PhD student Lukas Anneser is almost finished with the preparations for the learning experiment with the zebrafish larvae. He still has to get her to her "classroom". He sucks in water from a glass bowl with a large electric pipette.

Some of the fish swim in it, recognizable as tiny dark spots. He carefully lets water flow into a small plastic basin. It's a little bigger than a bar of chocolate. Glass walls divide it into several separate compartments.

The biologist places one mini fish alone in one compartment and three others together in the neighboring compartment. They form a small school. The lonely fish can see the others and swims where it is as close as possible to the school.

Positive experiences with black dots

Lukas Anneser and a colleague use this for learning training. You painted black dots on the transparent partition for the single fish. You can see these in addition to the swarm next door. You learn to connect the positive experience of being close to the crush with the points.

Later you get to see the neighboring compartment at one end only with black dots, without any conspecifics. The single fish can then choose whether to stay at the points or at the other end, where they can only see the empty neighboring compartment.

Lukas Anneser and his team have made many attempts of this kind. On average, there was a clear preference for the points. The fish have learned to associate the dots with a positive memory of the school.

Behavior without memory

Animals do not need a memory for some behaviors. Goslings stubbornly run after the first object they encounter after hatching from the egg. They think it's their mother. A spider doesn't have to dig into memory to know how to spin its web.

And a bee builds the honeycomb in the nest precisely without a plan. They all follow genetic programs. But innate behaviors are not enough for many other situations. Animals have to make choices. They collect the information for this in their memory. This can be a spatial memory, such as the jays sometimes need.

Only one of these birds hides thousands of acorns and nuts in his territory over the year. He buries most of them. When the landscape is covered in snow in winter and everything looks very different, the jay will still find its supplies with impressive certainty.

The jays treasure map

Thanks to a good memory, the birds keep a kind of treasure map in their heads. They remember where - seen from the hiding place - trees or other landmarks are. And in what direction and distance from these prominent points they buried their treasures.

Wild boars in Berlin know from experience: Before setting off on a nightly foray into settlement areas, they should wait for the time after the day's topics at the edge of the forest. Because immediately afterwards, dog owners take their four-legged friends for a walk again. Most bristle animals prefer to avoid them.

It takes arduous basic research to understand the simplest principles of memory. Much more complex is the memory of social interactions in higher living beings. And the more complex these are in a species, the more brain mass has developed in a species in the course of evolution, says a common hypothesis in zoology.

100 contacts saved

But the knowledge about the abilities of animals is increasing. They relativize our image of the uniqueness of humans. For some memory functions, some species even seem to us to be superior. The memory of the elephants, for example, is legendary.

Elephants have an incredible amount of information about other individuals with whom they have relationships. An elephant can recognize the individual calls of more than 100 conspecifics.

Professor George Wittemyer of Colorado State University in the USA heads an organization to protect elephants and has long been researching the life of these animals in the wild. Their social life may have helped them develop large, complex brains through evolution.

Herd without memory will not survive

That is one of the possible explanations. Another explanation could be the need to have highly accurate spatial maps of the environment in mind. This is being discussed as a further driver for the evolution of complex brains. Because elephants are among the mammals with the largest roaming and migrating areas.

The older elephants are, the more knowledge they have accumulated in their memories over the course of their lives. Therefore, herds of elephants are usually led by old, experienced females, the so-called matriarchs. When they are absent, the whole group lacks memory.

The ancient animals remember refuges from previous periods of drought, even if they were decades ago. You have vital knowledge for the whole group in your head. The younger ones can only acquire this over the years when they learn from the older ones.

When animals lose memory

If an old elephant dies before this transfer, the knowledge for the group is lost. This is what happens when poachers hunt and kill the large animals for their long tusks.

But just as in Europe, humans attack the wealth of experience and thus the survival of animals with their way of life. The brain and memory of bees, for example, are influenced by agricultural pesticides, warns Berlin bee expert Professor Randolf Menzel. Bees forget where to find their flowers or their hive. Or they no longer know how to communicate with their colleagues. You have lost your memory.

For researchers, there are still many unanswered questions about memory. For example: How does a memory keep, how much time has passed and how does it sort out memories that are no longer needed or are faulty?

Medical questions such as the treatment of Alzheimer's disease play a major role in human memory. Biologists, psychologists and physicians also do not yet know exactly how memory maps information about the past, present and future in such a way that humans and animals make decisions that ensure their survival.

SWR2 2018

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