Complex systems are very large systems comprising millions of agents interacting with each other and whose collective behaviour cannot be understood from the elementary features. In this sense the brain is the complex system par excellence: hundreds of billions of densely packed electrically excitable cells called neurons with hundred of millions of connections each. All exchanging electrochemical signals over short and long distances every few milliseconds and functionally interacting over multiple scales of time. Within this apparent chaotic bundle some deep questions arise. A single neuron is not in itself "intelligent" but a vast network of neurons can think, perceive, remember and generate the many extraordinary phenomena that they are collectively known as mind. How the mind can emerge from the interconnection between different neurons? How can single interactions between neurons organize themselves into manifestations collectively coherent like perception and movement
