Brain activity detection through EEG A BCI system needs an input from the user’s brain and these signals are converted in external operations; for this reason, brain signals have to be detected. EEG usually uses small ROCK inhibitors for glaucoma electrodes placed directly on the scalp at standardized positions. When a neuron is activated, a local current flow is produced and weak potential differences (5–100 μV) between electrodes are measured.

Inhibitors,research,lifescience,medical A large population of active neurons must be involved to generate electrical activity that can be detected with EEG over the scalp (Srinivasan et al. 1998). The electrodes record brain activity that is converted into digital signals and a sequence of steps translate this signals into commands. A limiting issue with EEG recording is its low spatial resolution, ranging between 2 and 3 cm. Moreover, EEG is deduced from apical Inhibitors,research,lifescience,medical dendrites of cortical pyramidal cells (Teplan 2002), thus

activity of deeper structures can only be studied indirectly. Because of the fluid, bone, and skin that separate the electrodes from the electrical activity, signals tend to be smoothed and noisy. This makes it difficult to locate the exact source of the oscillation. Inhibitors,research,lifescience,medical Nevertheless, EEG-based BCI have been shown to support a high performance, EEG is the predominant technology in BCI studies and most of clinical applications of BCI in patients with severe motor disorders have been demonstrated using EEG (e.g., Kubler et al. 2005; Vaughan et al. 2006; Nijboer et al. 2008). The changes in power of four frequency bands are used as control signals for BCI systems: delta (1–3 Hz), theta (4–7 Hz),

alpha (8–12 Inhibitors,research,lifescience,medical Hz), and beta (13–30 Hz). Four groups of electrophysiological Inhibitors,research,lifescience,medical signals in a BCI system As mentioned above, different noninvasive electrophysiological signals can be used as input for BCI systems. Therefore, BCIs can be classified into four groups based on the electrophysiological signals they use. Visual evoked potentials (VEP) VEPs are evoked electrophysiological potential that can be recorded throughout the visual system; they are extracted, using signal averaging, from the electroencephalographic activity recorded at the scalp. VEPs are elicited by visual stimuli such as flashes of light or flickering illumination presented on a screen. Users are presented with a panel whatever with different items and they have to fix their gaze on the item they want to select. The items on the screen are activated sequentially to elicit a visual evoked potential. BCI detects the VEP elicited by the stimulus where the subject looked at and the waveform of the VEPs depends upon the temporal frequency of the stimulus. In patients with neurological disease such as ALS, Sutter (Sutter 1992), for example, described communication problem with BCI due to artifacts caused by fasciculations.