All experimental methods that are carried out and used as part of the behavioral training and testing are painless and are based strictly on the principle of positive reinforcement. The animals are initially trained in a series of small steps to climb out of their enclosure and into a so-called primate chair via an accessible cage. The primate chair is a mobile base made of transparent Plexiglas in which the animals can sit upright and in which their bodies have sufficient space to move. The animals put their heads through an opening at the top of the chair. They learn this by slowly getting to know the chair over several weeks of training and are rewarded with fruit or treats for the behavior they learn. Chair training is complete when the animals sit upright in the chair of their own accord and accept the reduction of the upper opening without showing signs of stress or other noticeable behavior.
The animals are then shown the premises and the laboratories – again in several small steps – and given sufficient time to look around and familiarize themselves with the facilities. The same procedure is followed in the laboratory, where the subsequent tests are carried out.
To carry out these tests, it is necessary for the animal's head to be still. For this reason, it is restrained during the tests with the aid of a head holder, which is implanted once under anesthesia at the beginning of the testing. The animals are also accustomed to this procedure slowly and carefully. For the training to be successful, it is essential that the animal trusts the trainer completely and that the training is painless and stress-free. The institute's employees entrusted with such training have many years of extensive expertise and know exactly how to interpret the animal's behavior. The aim of this training is to ensure that the animal is familiar with all the details of the procedure as well as the subsequent testing procedure and shows no signs of stress.
As cognitive processes of the brain are studied at the institute, the animals learn tasks that require attention and memory skills, among other things. This can be, for example, a task in which the animal starts the task by pressing a lever and focusing its eyes on a fixation point presented in the middle of a screen. The animal is then shown cues that indicate, for example, which area of the screen or which type of object it should focus its attention on. Subsequently, several objects usually appear on the screen, of which the animal should only pay attention to the one that is at the previously displayed location or that belongs to the previously displayed object class. It should not turn its eyes away from the fixation point. As soon as the selected object changes its color or orientation or takes on a certain shape, for example, the animal releases the pressed lever to indicate that it has registered this change. Changes to other objects should be ignored.
This type of experimental design allows neuronal responses to be recorded for both objects that attract attention and those that are ignored, in order to understand the changes associated with attention in specific areas of the brain. In order for the animals to learn such tasks, they must be broken down into many small, sequential steps. The training of these tasks begins with the simplest, naturally spontaneous behavior, such as touching a button, which the animals can repeat at intervals of a few seconds and for which they are rewarded with liquid. Over the following weeks, the task is modified step by step, for example so that the button must not only be touched but also pressed down, or must always be pressed down when a green dot lights up on a monitor, etc. In this way, the animals are able to learn even very complex behavioral tasks over a period of many months. The animals work on the respective task on each training day for as long as they wish. Due to their species-specific behavioral repertoire, they quickly learn to consume enough fluid during training to keep them well hydrated until the next time.