Remember Pavlov and his dogs? This researcher, who left theology for medicine and physiology, conducted repeated pairings in which an initially neutral stimulus, such as a bell, accompanied the dogs’ food. He observed that after such training, the animals salivated at the sound of the bell, even if presented with no food.

Conditioning was born, with important implications for the development of behaviourism. The conditioned response, which is a type of learning, represents a nice example to understand how and why many species use experience to learn and to predict reward. And yes, more or less consciously, we are constantly predicting and 'hunting' rewards.