**2. Common EEG patterns**

## **2.1 EEG**

In most of the Neurosurgery hospitals or the hospitals where the diagnosis of the human brain takes place, they mostly use EEG which have very high Temporal and spatial resolutions, devices also occupy huge amounts of space. But in the study of Brain Computer Interface wherein we are required to develop the applications to control the external environment in such a way that the patient or subject or the user must not be facing the adaptability issues to significant extent [14]. If we observe the EEG devices which are used in the Hospitals, they generally require minimum of 2 to 3 hours for just equipping the device or placing the electrode in proper locations over the scalp, where in the contact optimizing fluid needs to be applied all over the head and the electrodes needs to be placed which is a tedious and complex process. But recently the company Emotiv has come up with a very sophisticated and easily adaptable device named as INSIGHT. This Insight device is equipped with very efficient specifications, where in which It has 3 axis gyroscope and 3 axis Magnetometer which are very helpful to remove the artifacts due to the head movements which is absent in the case of hospital EEGs (therefore the patients is instructed not to move their head/to avoid the motor movements). There are 5 important electrodes installed in the device which are made of semi-dry polymer. The electrode locations are 2 in the frontal region, 2 in the temporal region and another is at the central peritoneal region. The nomenclature of these electrodes are given according to the international 10–20 system. Where the frontal left electrode is named as AF3, frontal right electrode is named as AF4, temporal left electrode is named as AT7, temporal right electrode is named as AT8 and peritoneal central electrode is named as Pz plus DRL reference mastoid electrode on the left, the channels with built in digital 5th order sinc filter, bandwidth of 0.5-43 Hz with digital notch filters at 50 Hz and 60 Hz, 2.4 Hz wireless connectivity, 8400uV is the dynamic range (input referred), sequential sampling, 128 samples per second is the sampling rate, 14bit motion resolution, the electrodes are

semi dry polymers, with 14bits 1 LSB = 0.51muV (16 bit ADC, 2 bits instrumental noise floor discarded) EEG Resolution. Main principle of EEG devices is the differential amplifier which has 2 inputs Input 1 and Input 2. From both the inputs the information is fed, the information can be mathematical or any signal it gives the output resultant signal which is the relative deference chunk of signal. Mounting the device over the subject's scalp is a crucial procedure, where saline glycerol solution is applied to the semi dry electrodes in order to maintain the optimum contact quality with the scalp of the head. The electrodes were being placed in active locations according to the International 10–20 system protocol and the optimal 100% contactivity is ensured. The subject is instructed to not to move to avoid motion artifacts and stay focused on mental commands. Connection between the insight and the laptop is achieved by following the EmotivApp protocol, connection can be established either using Insight dongle or through the Bluetooth connection. Authentic Interpretation of EEG requires a very high amount of training and experience in analyzing and predicting the Graphical data. The most important set of rules which needs to be followed while analyzing the EEG data is the type of montages used, the time domain of the subject state compared to the EEG data at that current time in order to check that there are no external noises or movements made by the subject. There are different types of montages such as longitudinal bipolar Montage, longitudinal-transverse bipolar montage, circumferential bipolar montage, temporal bipolar montage, Cz referential Montage, Ipsilateral ear referential Montage in order to analyze the patient's cognitive state in different ways in order to predict the correct result. In the EmotivePro app in MacBook Air laptop to record raw EEG data for the experiments I have used an Ipsilateral ear referential montage where one input of the differential amplifier will be a DRL reference mastoid electrode and the other input will be any one of the active electrodes. I set up the channel spacing to 400 μV minimum amplitude to 100 μV, maximum amplitude to +100 μV, with a high pass filter.
