**2.1 Brain signals**

EEG is our main focus in this chapter, and its use is widely popular due to low cost, low risk, portability and easy to set up. The downside would be poor signal quality and low spatial resolution. The signal can also be affected by external noise and artifact, along with mood and posture of the subjects. Upright posture can improve EEG quality due to stronger high-frequency content [2–4]. These brain signals can be classified as endogenous (spontaneous) and exogenous (evoked). The commonly used endogenous patterns are slow cortical potential (SCP) and sensorimotor rhythm (SMR); whereas, exogenous patterns are visual evoked potential (P300) and steady state visual evoked potentials (SSVEP) [1].
