*2.1.1 Slow cortical potential*

Slow cortical potential arising from intracortical or thalamocortical region is projected to different cortical layers that harbor apical dendrites of pyramidal neurons. Firing from these neurons can generate motor or cognitive tasks. A negative voltage shift causes depolarization of the cortical network, while a positive voltage shift an inhibition (**Figure 1**). Intense training is required to control the shifting in the SCPs in order to perform basic tasks. As a result, these long training hours might hinder the popularity of the use of such brain signals [1].

**Figure 1.** *Mean traces of positive SCP and negative SCP of a BCI data set.*

*Brain-Computer Interface: Use of Electroencephalogram in Neuro-Rehabilitation DOI: http://dx.doi.org/10.5772/intechopen.110162*

#### *2.1.2 Sensorimotor rhythm*

The sensorimotor rhythm arising from sensorimotor areas generates β (beta) and μ (mu) rhythm mainly used for specific voluntary regulations such as preparation, control and execution of motion. Merely the thought of a movement (**Figure 2**), without any external stimuli, can regulate the rhythm amplitudes in these central motor areas, which makes it appealing for users with severe motor disabilities. The change in the power of band frequency helps differentiate the type of mental tasks being carried out. A decrease in band frequency termed event-related desynchronization (ERD) occurs up to 2 seconds before the actual movement. Event-related synchronization (ERS) signifies an increase in the band frequency that occurs before the end of a movement. The classes of movement that can be identified through SMR are left hand movement, right hand movement, movement of the feet and movement of the tongue. But the movement between left and right foot and between particular fingers of one hand are indistinguishable due to their small representation in the cortical homunculus. Again, it requires intensive training and sufficient mental capacity and attention to generate this motor imagery-based EEG signals [1, 4].

#### *2.1.3 Visual evoked potential*

Visual evoked potential (P300) occurs at 300 milliseconds after a triggering stimulus (**Figure 3**). Because the potential occurs with high consistency, this positive voltage peak has been used to mark an event. Although it requires less extensive

#### **Figure 2.**

*Effects of motor imagery on sensorimotor rhythm. On the top shows the frequency spectra during movement at rest (dashed line) and during imagination (solid line). During imagination, the amplitude of EEG tracing is attenuated as shown on the bottom.*

#### **Figure 3.**

*Visual evoked potential. This is initially stimulated by flashes on the screen, then captured by the brain producing a positive voltage potential occurs at 300 ms after the stimulus.*

training compared to SCP and SMR, the usefulness of P300 may be hampered by the severity of motor disabilities and degree of fatigue. Another visual evoked potential, called steady state visual evoked potentials (SSVEP), requires users' attention and the ability of visual fixation. The potentials are triggered by an oscillating stimulus at a fixed frequency, like a flashing letters or digits on a screen. That results in an increase in EEG activity, or SSVEP response, at the occipital area with the same frequency as the stimulus. However, the requirement of an intact oculomotor function and gaze fixation for a period of time has been challenging for some groups of patients. A study performed on amyotrophic lateral sclerosis (ALS) patients did not have much success due to their inability to control eye movement [1].
