The design and execution of an experiment depends very much on the question being asked. If we want to find out which stimuli the neurons in a certain brain region react to, it is often enough to anesthesize the animal and study single neurons with microelectrodes. Sometimes the experiment can be designed in such a way that the animal does not even need to wake up from anesthesia, so the animal is subjected to as little stress as possible. If, however, we want to find out which brain regions react especially well to certain stimuli, an anesthetized animal can be studied for a few hours in the MRI scanner and then brought out of anesthesia.
If we are studying cognitive functions, on the other hand, the animal must be alert in order to be able to solve a certain task. The method used to measure brain activity depends on whether we want to examine the spatial extent of neural networks or the temporal coordination of a great many neurons. The first step is to accustom the animal to the laboratory environment. Training itself cannot begin until the animal is sufficiently at ease with the experimental set-up. Using positive reinforcement with water or juice the monkey is taught to carry out a cognitive task. Depending on the level of difficulty, this can take several months to as much as a year. As soon training is successfully completed, we can carry out the experiment itself and measure brain activity while the monkey is performing the behavioral task. Both during the training phase and during the measurements, the animal must be given enough breaks during which it does not work. A well-trained animal can be used in a number of different experiments over a period of several years. This not only allows us to track complex cognitive functions over different processing stages in the brain, but also helps reduce the total number of animals needed.
Although the animals must work on a regular basis, they are given plenty of time to relax between experiments so that they don’t lose their motivation. It is impossible to force a monkey to perform a cognitive task, and it will only cooperate and concentrate if it feels at ease and not stressed.
As mentioned above, the monkey receives a water or juice reward if it solves a task correctly. This does not mean that it is forced to go thirsty for an extended period of time if it does not cooperate. The monkey physiology is well adapted to not having constant access to water, for in the wild the animals must go without water for long periods of time when they move from one water hold to the next. The brief water deprivation used in our experiments is carefully monitored by our veterinarians and animal caretakers. In addition to water and juice, our animals receive enough fluids in their daily ration of fresh fruit and vegetables.
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