**5. Brain computer interface**

*Electroencephalography - From Basic Research to Clinical Applications*

the international 10–20 system (**Figure 3**) [19, 20].

created by dipoles as a result of excitation of the epical dendritic postsynaptic potential at the cortical pyramidal cells [18, 19]. The measurement and assessment of the electric field potentials can be made by attaching conductive electrodes to the human scalp. At the present time the wet electrodes are the gold standard used for EEG study [19]. A conductive paste or gel need to be used during the application of wet electrodes to minimize electrode-skin impedance in order to achieve good conductivity of the electrical impulse. The typical value of skin impedance should be kept between 5 and 20 KΩ. This skin impedance should be continuously monitored during the EEG study to ensure proper and high-quality conductivity between the skin and the EEG electrode. Performing an EEG study is a time consuming process which require an expert EEG technician or neurophysiologist in order to obtain good quality EEG results for proper interpretation and reporting as the reading and analyzing EEG data is a hard task and must be interpreted by expert neurophysiologists. The location site and description of the scalp electrodes is well recognized by

During the first EEG only 20–50% of patients with seizure disorder show interictal epileptiform discharges (IED) so the yield of the EEG study can be enhanced by many activation methods in order to capture the interictal epileptiform discharges which help confirming the diagnosis of epilepsy and seizure disorder [22]. The common activation procedure used in EEG laboratories includes Hyperventilation, intermittent photic stimulation (IPS), sleep and sleep deprived techniques. Hyperventilation (HV) is considered to be the first and oldest activation method used to trigger the interictal epileptiform discharges (IED) especially the one associated with absence epilepsy. HV is more effective in Pediatric population than in adult. A proper effective HV should be carried out for full 3 minutes with continuous recording and monitoring for one-minute post hyperventilation. HV is more efficient in diagnosing generalized seizures than focal epilepsy. The mechanism of HV to trigger interictal epileptiform discharges can be explained by hypocapnia induction which also manifest as background slowing or focal slowing in the EEG [22]. HV is a major provocation technique used to trigger the typical 3-Hz spike-and-wave discharge (SWD) which is characteristic for absence epilepsy as more than 90% of patients who have absence epilepsy show SWD during HV. The non-specific thalamic projection system (NSTPS) which is a part of the thalamocortical networks triggered by respiratory alkalosis and considered to be the major induction of SWD associated with absence epilepsy during the process of HV [23]. HV is an efficient and safe activation method for epilepsy and seizure disorder provocation however there are certain contraindication to perform HV during EEG study which includes patients with cardiopulmonary disease, sickle

**138**

**Figure 3.**

*The international 10-20 system [21].*

A Brain Computer Interface (BCI) which also named as Brain –machine Interface (BMI) is a computer- build network system that allow direct communication between cerebral brain activity and external recordable machine without using human muscles or peripheral nervous system. BCI utilize and analyzes the brain signals to collect information and send them to output system. BCI network consists of five phases: Signal Acquisition, Signal Magnification, Feature Extraction, Categorization and Control Interface. BCI assesses and analyze brain activity through mainly electrophysiological and hemodynamic studies. The electrophysiological study consists mainly of EEG, electrocorticography and magnetoencephalography. The hemodynamic study measures glucose uptake by an active neurons and this can be evaluated by procedures like functional magnetic resonance and infrared spectroscopy. BCIs commonly used EEG to gain details from brain activity. The design of BCI is complex due to restricted resolution and data reliability detected by the brain [25, 26].

## **6. Different types of EEG study**

The American Clinical Neurophysiology Society suggest at least 20 minutes' time duration for routine outpatient study. However, the International League against Epilepsy suggests a minimum 30 minute for routine EEG recording. Currently most routine EEG studies are done with an average time between 20 and 30 minutes. The abnormal epileptiform discharges found in 29–55% in patients with epilepsy on their first routine EEG study. Ambulatory prolonged EEG study is considered to be helpful diagnostic technique to capture interictal epileptiform discharges (IEDs) in epilepsy patients whom their first routine EEG studies reported normal. Prolonged ambulatory EEG study is considered to be superior to routine EEG in identifying IEDs specially during the natural sleep state. This procedure is also helpful to differentiate epileptic from non-epileptic psychogenic events. The duration of the ambulatory EEG study usually between 24 to 96 hours [27, 28].

Epilepsy Monitoring Unit (EMU) is an important and crucial part of the neurophysiological work up for the diagnosis and classification of epilepsy and evaluation of psychogenic non-epileptic seizures (PNES). EMU is also essential for patients

with intractable epilepsy resistant to antiepileptic medications and for evaluating candidates for possible epilepsy surgery [29].

EMU is strongly recommended for children with unclear history of paroxysmal episodes in order to differentiate between epileptic and non-epileptic events as this can be quite challenging in pediatric population. EMU is also important in evaluating different types of epilepsy syndromes in children. One of the vital advantages of the video-EEG telemetry is the monitoring and recording the ictal events especially in patients with partial epilepsy. EMU is a highly selective study should be done for carefully selected patients as this is an expensive and time consuming procedure [30]. The process of monitoring and recording video-EEG telemetry can range from 24 hours to 7 days. In some situation antiepileptic drugs need to be tapered in order to induce seizure activity for better evaluation of seizure semiology and localization of the epileptogenic zone [31].

The Amplitude-Integrated EEG (aEEG) is another continuous electrophysiological modality used in both term and preterm newborns in the neonatal intensive care units (NICUs). Since it's first introduction late in 1980s. the aEEG considered to be the gold standard to monitor and assess neonatal brain background activity, diagnose and manage newborn seizure disorders and help in selecting newborns who might be benefit from cooling therapy. The aEEG also plays a major role in predicting the neurodevelopmental outcomes for term and preterm newborn babies. The application and recording of the aEEG is done by using two or four scalp electrodes applied to C3, P3, C4 and P4 positions of the newborn head according to the international 10–20 system. aEEG is a safe procedure which has a major limitation as it covers only small area of the head surface and hence focal epileptiform activity cannot be monitored during the aEEG recording [32–34].

EEG is considered to be the commonest procedure used for intraoperative neurophysiological and cerebral perfusion monitoring [35]. EEG is also considered to be the gold standard modality for evaluating patients for possible epilepsy surgery to localize and define different epileptogenic foci. EEG also plays an important role in understanding the nature and pathophysiology of epilepsy and presurgical evaluation of functional cortical mapping. However, routine EEG monitoring might not be always sufficient to evaluate certain types of epilepsy such as non-lesional temporal lobe epilepsy which necessitate the need of more interventional procedure such as the invasive electroencephalography (iEEG) [36, 37].

## **7. Basic EEG interpretation**

A proper and detailed history taking is more reliable and important in diagnosing epilepsy and seizure disorders than EEG study. A solid and classical history of seizure even with the presence of normal EEG finding make the diagnosis of epilepsy is more likely as the sensitivity of single routine EEG study is only about 50% in diagnosing seizure disorders [38].

A single EEG study provides extensive data for interpretation. The main initial description of the EEG recording includes the amplitude, frequency and wave morphology. Hans Berger described two characteristic EEG wave frequencies during awake state: The alpha rhythm (8–12 Hz) which is more prominent in the arousable stage with eye closure and beta rhythm (13–30 Hz) commonly seen with mind focus state. In most people eye closure will result in frequency transfer from beta to alpha rhythms. Subsequent wave frequencies were identified the theta rhythm (4–7 Hz) and the delta rhythm (0.5–3 Hz) which are predominant during sleep in adults, and the gamma rhythm (> 30 Hz) which is associated with memory, information processing and cognitive skill (**Figure 4**) [39].

**141**

**Figure 6.**

**Figure 4.**

**Figure 5.**

*Hypnagogic hypersynchrony. A normal EEG variant [42].*

*High amplitude rhythmic slowing with hyperventilation [43].*

*Different EEG waveforms [39].*

*Basic Electroencephalogram and Its Common Clinical Applications in Children*

*DOI: http://dx.doi.org/10.5772/intechopen.94247*

*Basic Electroencephalogram and Its Common Clinical Applications in Children DOI: http://dx.doi.org/10.5772/intechopen.94247*

#### **Figure 4.**

*Electroencephalography - From Basic Research to Clinical Applications*

seizure semiology and localization of the epileptogenic zone [31].

such as the invasive electroencephalography (iEEG) [36, 37].

information processing and cognitive skill (**Figure 4**) [39].

**7. Basic EEG interpretation**

seizure disorders [38].

candidates for possible epilepsy surgery [29].

with intractable epilepsy resistant to antiepileptic medications and for evaluating

EMU is strongly recommended for children with unclear history of paroxysmal episodes in order to differentiate between epileptic and non-epileptic events as this can be quite challenging in pediatric population. EMU is also important in evaluating different types of epilepsy syndromes in children. One of the vital advantages of the video-EEG telemetry is the monitoring and recording the ictal events especially in patients with partial epilepsy. EMU is a highly selective study should be done for carefully selected patients as this is an expensive and time consuming procedure [30]. The process of monitoring and recording video-EEG telemetry can range from 24 hours to 7 days. In some situation antiepileptic drugs need to be tapered in order to induce seizure activity for better evaluation of

The Amplitude-Integrated EEG (aEEG) is another continuous electrophysiological modality used in both term and preterm newborns in the neonatal intensive care units (NICUs). Since it's first introduction late in 1980s. the aEEG considered to be the gold standard to monitor and assess neonatal brain background activity, diagnose and manage newborn seizure disorders and help in selecting newborns who might be benefit from cooling therapy. The aEEG also plays a major role in predicting the neurodevelopmental outcomes for term and preterm newborn babies. The application and recording of the aEEG is done by using two or four scalp electrodes applied to C3, P3, C4 and P4 positions of the newborn head according to the international 10–20 system. aEEG is a safe procedure which has a major limitation as it covers only small area of the head surface and hence focal epileptiform activity cannot be monitored during the aEEG recording [32–34]. EEG is considered to be the commonest procedure used for intraoperative neurophysiological and cerebral perfusion monitoring [35]. EEG is also considered to be the gold standard modality for evaluating patients for possible epilepsy surgery to localize and define different epileptogenic foci. EEG also plays an important role in understanding the nature and pathophysiology of epilepsy and presurgical evaluation of functional cortical mapping. However, routine EEG monitoring might not be always sufficient to evaluate certain types of epilepsy such as non-lesional temporal lobe epilepsy which necessitate the need of more interventional procedure

A proper and detailed history taking is more reliable and important in diagnosing epilepsy and seizure disorders than EEG study. A solid and classical history of seizure even with the presence of normal EEG finding make the diagnosis of epilepsy is more likely as the sensitivity of single routine EEG study is only about 50% in diagnosing

A single EEG study provides extensive data for interpretation. The main initial description of the EEG recording includes the amplitude, frequency and wave morphology. Hans Berger described two characteristic EEG wave frequencies during awake state: The alpha rhythm (8–12 Hz) which is more prominent in the arousable stage with eye closure and beta rhythm (13–30 Hz) commonly seen with mind focus state. In most people eye closure will result in frequency transfer from beta to alpha rhythms. Subsequent wave frequencies were identified the theta rhythm (4–7 Hz) and the delta rhythm (0.5–3 Hz) which are predominant during sleep in adults, and the gamma rhythm (> 30 Hz) which is associated with memory,

**140**

*Different EEG waveforms [39].*

#### **Figure 5.**

*Hypnagogic hypersynchrony. A normal EEG variant [42].*

It is vitally important to ensure proper education and gain enough experience to read and interpret EEG recording in order to avoid misdiagnosis of epilepsy and to provide better care to the patient. It is also essential to appreciate the common benign variations of normal EEG study [40, 41].

A common normal patterns seen in EEG study which can be falsely interpreted as abnormal epileptiform discharges include multifocal sharp waves and spikes, generalized slowing with hyperventilation, hypnagogic hypersynchrony and most commonly is the background alteration at the temporal area (**Figures 5** and **6**) [38].

Over interpretation of normal EEG tracing is the main factor for misdiagnosis of epilepsy and seizure disorders. Improper neurophysiological training and inadequate experience is the major reason for over interpretation of normal EEG study. Conservative EEG interpretation and avoiding biased history are strongly recommended by all epileptologists [38].
