2.1. Background
Before refers to the concept of BCI as conceived currently, it is important to mention the origins of EEG. The first references about brain electrical activity recording go back to 1875 taken from the cortical surface in animals (Canton, 1875) and 1933 taken from the human scalp (Berger, 1993). Thanks to these two remarkable historic events, BCI found its origins by 1970 decade when it was possible to detect and classify some evoked responses known as epochs (Vidal, 1977). Early work involved a lot of experimentation with monkeys using invasive methods to acquire the EEG signals. Important neural activity in their motor cortex area was found when they accomplished several tasks stimulated by rewards.
During these years, many research teams were established to work on this field and trying to understand BCI nature using cognitive neuroscience, computing and mathematical models, or a combination of them. Several research projects were supported in improving signals quality, acquisition methods (invasive and non-invasive), temporal and spatial resolution and classification algorithms. As early state-of-art work, it was developed by 1991 one of the first EEG BCIs able to provide a sort of cursor control over a video screen (Wolpaw, McFarland, Neat, & Forneris, 1991).
However, the main achievements have been done during the last 15 years. Innumerable research results have been published since then, making its tracking almost impossible. Uncountable are the contributions from different areas such as materials science, digital signal processing, machine learning, electronics, computing, medicine as many others. All of them have contributed to the relative success of the BCIs up to today, creating a complete field for research.