How birds learn to plan their actions

Experience teaches us to associate objects with meaning – we learn that a stop sign or a red traffic light mean that we have to stop. This example shows that objects of different visual appearance often have a similar ‘behavioral relevance’ – as it is called by experts. The ability to classify objects according to behaviorally relevant criteria is an essential prerequisite for goal-directed behavior. Scientists around Janina Kirsch and Onur Güntürkün from the Ruhr University Bochum, together with Ad Aertsen from the Bernstein Center and the University of Freiburg, have studied how behaviorally relevant categories evolve in the brain of birds during the learning process.

In their experiments the scientists trained pigeons to respond to images that were presented to them with a certain behavioral pattern. More precisely: when the birds saw the shape of a heart or a lightning they were supposed to ‘mandibulate’, i. e. to move the beak. If they solved the task correctly, they received a reward. When they saw a triangle or a cross, however, they only received a reward if they did not move their beak. During the experiments, the scientists recorded the activity of individual nerve cells in the ‘nidopallium caudolaterale’ (NCL) of the birds, a brain region that is assumed to be responsible for the planning of actions and so fulfils a similar function as the ‘prefrontal cortex’ of mammals and humans.

Pigeon with brain (relative location).

The scientists investigated two pigeons, a ‘beginner’ pigeon and an ‘experienced’ pigeon that had more practice in solving the tasks. In the NCL of both pigeons, the majority of neurons responded according to the behavior that was indicated by the images. For example, they only responded in trials in which the animal was supposed to mandibulate – no matter whether a heart or a lightning was shown. Thus, in this brain region information is represented according to behaviorally relevant criteria.

But neurons of the beginner animal and the experienced animal differed both with regard to the precision in differentiation as well as to the timing of their response. The cells of the beginner pigeon mostly responded much later in a trial than those of the experienced animal – namely only when the reward was received. ”The animal interprets its behavior in retrospect and its neurons respond accordingly”, Kirsch explains these observations. “In contrast, the experienced animal knows already upon presentation of the image what behavioral instruction it contains. So, already at this point, the cells respond according to the behavioral categories.” The results contain important hints on how the meaning of objects and images is learned and represented in the brain of birds.