Book excerpt: For a few decades, the puzzle of consciousness, which for centuries was analysed by philosophers, has been finding a wide interest in the scientific field, where previously it was not entitled to be a member. It has become one of the most-debated problems in the cognitive sciences. The anatomical bases, neurophysiological correlates and elementary mechanisms underlying complex processes arising with consciousness have been compared with the psychological (perceptive, cognitive, volitive, emotional) aspects of conscious expressions, in normal and pathological conditions. Various theories, which attempt to fit systematically and coherently neural and psychological data, have been debated, proving the emergence of the phenomenon of consciousness.