**3.1 Slow cortical potential**

Slow cortical potential as mentioned previously requires subjects to control the upward and downward shifting of polarity to select letters, words or pictograms. A system is developed to allow subjects to communicate through writing: first phase requires basic training for regulating own SCP amplitude by mental strategies either above or below a certain threshold to move the cursor at a specific space or time; and, the second phase requires selecting and rejecting letters by self-managing own SCP amplitudes to form words and phrases. One study also helps subjects to browse the Internet by training them to self-regulate SCP amplitudes to move up or down the cursor in order to select or discard a command [1].

#### **3.2 P300 evoked potential**

P300 is late positive evoked potential occurs after an external task-stimulus. The users are given different options of commands or stimuli, and the system needs to detect which stimuli can elicit P300 to exert its role on various systems like painting, spelling, web browsing and controlling of external devices [1]. Various BCI-controlled humanoid applications have been discussed in [6] like grasping a glass of water by robotics in ALS patients, controlling the navigation of a robot via telepresence. Using hybrid BCI by combining the brain signals (P300) and the biological feedback signals generated by some other parts of the body are also seen in executing the command [6]. The advantage of using P300 is its high accuracy. However, the performance is not consistently at a high level, mainly affected by the severity of the disease and the lack of motivation by repeatedly doing the same training routine [1].

## **3.3 Sensorimotor rhythm**

Sensorimotor rhythm requires subjects to use mental strategies or motor imagery to enable motor execution (ME). For subjects who have motor disabilities, the thought of movement can suppress EEG rhythm leading to desynchronization, resulting in movement initiation. Motor imagery can enhance motor learning process by neuroplasticity [7, 8]. With both MI and ME derived from sensorimotor areas such as primary motor area, supplementary motor area and premotor cortex, SMR can be manipulated to help the disabled towards rehabilitation. The differences in the

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

BCI performance may be related to the number of folds and thickness of individuals' cortices which may have an impact on the functional networks. The emotional and mental processes such as fatigue, memory load, attention and reaction time, along with gender, age and lifestyle all contribute to the inter- and intra-variability in SMRbased BCI motor performance. Overall, subjects with high motor variability including force field adaptation, speed/trajectory, motivational factors and strong resting EEG amplitudes have a higher probability of achieving better BCI performance, hence better neuroplasticity and rehabilitation outcome [8].

Many BCI systems have been using SMR by means of spelling, cursor movement, and control of external devices for communication to the external world. Creating a virtual environment to work under, subjects are more motivated in controlling movement in this framework resulting in better performance with fewer runs of training [1].
