Deep Learning have been three waves of development: The first wave started with cybernetics in the 1940s-1960s, with the development of theories of biological learning and implementations of the first models such as the perceptron allowing the training of a single neuron. The second wave started with the connectionist approach of the 1980-1995 period, with back-propagation to train a neural network with one or two hidden layers. The current and third wave, deep learning, started around 2006.