Training and Procedures

The study investigates the decision-making behavior of macaques along with the associated neural processes in the brain. For this, the animals are trained by experts over several months.

The animals learn to sit in a “primate chair” that faces a screen and to solve behavioral tasks similar to those given when diagnosing mental illness in humans. While the animals solve the tasks, the activity of their nerve cells in the prefrontal cortex is measured.

Solving complex behavioral tasks on the screen requires the macaques’ full cooperation and is therefore only possible with relaxed, stress-free animals. The primates learn the procedure – leaving their enclosure, entering the transfer box, sitting in the primate chair, solving the tasks – over months of gradual training with a specially trained caregiver. The relationship with the animals, and thus their behavior, is based on trust and cooperation.

To measure the animals’ brainwaves while they solve behavioral tasks on the screen, a tiny plate is implanted in the prefrontal cortex. In this surgical procedure, the macaques receive medical care before, during and after implantation, and are administered painkillers so they are not in discomfort. Because the brain is insensitive to pain, the tiny implant does not disturb the animals. The brain implants are comparable to those employed in humans for the treatment of Parkinson’s disease and epilepsy.

During the experiment, the animals’ eye movements are also recorded. For this purpose, a small restraint is applied to the top of the macaque’s skull to keep its head still during cognitive tasks. This is the only way to precisely record eye movements made in conjunction with the macaques’ decisions and to subsequently correlate the movements with the underlying neural processes. By gradual and playful means, the animals are accustomed to having their heads immobilized. With training they become familiar with the immobilization as part of the experimental procedure – a procedure they may interrupt at any time. The animals have unrestricted access to food and water throughout the training.

The macaques are given a reward for each task they solve – for example, a sip of diluted fruit juice, a raisin or a piece of mango. During their training, the animals’ access to water or food while they are in their enclosures has in no way been restricted to any specific times. The rewards that Paul and Alan get during training without having to compete with the two higher-ranking macaques are enough to motivate them to take part voluntarily. The welfare of the animals is crucial to the success of the research. An animal that feels stressed by the experiments would be unable to muster the focus and calm required to solve the behavioral tasks.

The health and welfare of the animals is regularly monitored by a veterinarian. Each application stipulates strict criteria requiring the experiments to be abandoned if a macaque feels discomfort or experiences ill health. In addition, the University of Zurich’s in-house animal welfare officers, the Cantonal Veterinary Office and the Commission on Animal Experimentation monitor the animals’ well-being during the entire study. The veterinary office may review the trials and assess how the animals are kept at any time, and the commission must inspect the way the animals are kept at least twice a year. As a voluntary additional measure, around-the-clock video recordings of the animals are made and placed at the disposal of the regulatory authority of the Cantonal Veterinary Office.