Electroencephalogram (EEG) is a measure of brain activity that contains abundant information about human brain function. For this reason, recent clinical brain researches and Brain-Computer Interface (BCI) studies use EEG signals in many applications. We studied a particular Event-related Potential, named Readiness Potential, connected to volitional motor intention, to explore cognitive functions in patients with Disorders of Consciousness as Coma, Vegetative State, and Minimally Consciousness State. We studied the neural correlates of intention to move in order to investigate the self-awareness and of the environment. In the early 1980s, B. Libet found that RP starts about 550 ms prior to freely voluntary acts, but the consciousness of the act occurs about 200 ms before the EMG onset.