Electroencephalography (EEG) produces time-series data of neural oscillations in the brain, and is one of the most commonly used methods for investigating both normal brain functions and brain disorders. Quantitative EEG analysis enables identification of frequencies and brain activity that are activated or impaired. With studies on the structural and functional networks of the brain, the concept of the brain as a complex network has been fundamental to understand normal brain functions and the pathophysiology of various neurological disorders. Functional connectivity is a measure of neural synchrony in the brain network that refers to the statistical interdependency between neural oscillations over time. In this review, we first discuss the basic methods of EEG analysis, including preprocessing, spectral analysis, and functional-connectivity and graph-theory measures. We then review previous EEG studies of brain network characterization in several neurological disorders, including epilepsy, Alzheimer’s disease, dementia with Lewy bodies, and idiopathic rapid eye movement sleep behavior disorder. Identifying the EEG-based network characteristics might improve the understanding of disease processes and aid the development of novel therapeutic approaches for various neurological disorders.

Citations

• Augmented Recognition of Distracted Driving State Based on Electrophysiological Analysis of Brain Network
  Geqi Qi, Rui Liu, Wei Guan, Ailing Huang
  Cyborg and Bionic Systems.2024;[Epub]     CrossRef

Background
A dry-type electrode is an alternative to the conventional wet-type electrode, because it can be applied withoutany skin preparation, such as a conductive electrolyte. However, because a dry-type electrode without electrolyte has highelectrode-to-skin impedance, an impedance-converting amplifier is typically used to minimize the distortion of the bioelectricsignal. In this study, we developed an active dry electroencephalography (EEG) electrode using an impedance converter, andcompared its performance with a conventional Ag/AgCl EEG electrode. Methods: We developed an active dry electrode withan impedance converter using a chopper-stabilized operational amplifier. Two electrodes, a conventional Ag/AgCl electrodeand our active electrode, were used to acquire EEG signals simultaneously, and the performance was tested in terms of (1)the electrode impedance, (2) raw data quality, and (3) the robustness of any artifacts. Results: The contact impedance ofthe developed electrode was lower than that of the Ag/AgCl electrode (0.3

Restless legs syndrome (RLS) is a sensorimotor neurological disorder in which the primary symptom is a compellingurge to move the legs, accompanied by unpleasant and disturbing sensations in the legs. Although pathophysiologicmechanism of RLS is still unclear, several evidences suggest that RLS is related to dysfunction in central nervous systeminvolving brain and spinal cord. L-DOPA, as the precursor of dopamine, as well as dopamine agonists, plays an essentialrole in the treatment of RLS leading to the assumption of a key role of dopamine function in the pathophysiology ofRLS. Patients with RLS have lower levels of dopamine in the substantia nigra and respond to iron administration. Iron,as a cofactor in dopamine production, plays a central role in the etiology of RLS. Functional neuroimaging studies usingPET and SPECT support a central striatal D2 receptor abnormality in the pathophysiology of RLS. Functional MRIsuggested a central generator of periodic limb movements during sleep (PLMs) in RLS. However, to date, we have nodirect evidence of pathogenic mechanisms of RLS.

Backgrounds and Objectives: Despite of enormous clinical and laboratory researches focused on the useful markersin status epilepticus(SE), clinically applicable methods are not yet available. Although ketogenic diet (KD) is an oldmethod of treating epilepsies, its outstanding antiepileptic effect in some epileptic patients needs re-evaluation of thismethods. This study was performed to evaluate the effect of KD on the change of nitric oxide(NO) during the SE.Methods: After the determination of critical EEG stages in the pilocarpine-induced SE model, serum NO levels weremeasured with Griess reaction. Open cardiac puncture was done immediately after the four different EEG stages of SEin the KD rats and regular diet (RD) rats. Cessation of SE was done with the 10~20 mg/Kg of diazepam i.p. injection ineach stages of SE in KD and RD rats.Results: Pilocarpine-induced SE showed reliable EEG and behavioral patterns in all rats. Also, KD did not affect theSE induced by pilocarpine in terms of the SE induction time and SE severity. Serum NO was consistently higher in KDrats than RD rats in all SE stages.Conclusions: KD significantly increases NO during the pilocarpine-induced SE. These finding might contribute theneuroprotective effect of KD in the SE.

Background
: Subtle status epilepticus (SE) is an end-stage of convulsive SE. This phenomenon might be a clinical expression of neuronal exhaustion caused by substained electrical discharges. As subtle SE may show diverse clinical features, early detection depends on clinical suspicion. Case : A 68-year-old woman was presented with repetitive involvement of right limbs after two generalized tonic-clonic seizures. She experienced right middle cerebral artery infarction 4 months ago, and after the event, left side hemiplegia sustained. These seizures were first-ever after the cerebral infarction. Orientation and verbal responses were fairly preserved but general cognitive function was minimally slowed. During the video-EEG monitoring, repetitive sharp waves were noted in the right hemisphere and these sharp waves occasionally spread to the contralateral side. Her right side involuntary movement was identifiable when the epileptic discharges were found on her right hemisphere. Conclusion : We suggested that this unexpected convulsive movement is a reflection of earlier exhaustion in the right hemisphere of deefferentation of right hemisphere because of preexisting neuronal damage.

Background
and Objective : Epileptic seizures are frequent complication of lobar hemorrhage. We investigated thefactors affecting development of epilepsy following spontaneous lobar ICH.Methods : From January 1986 to July 1999, 114 patients were admitted to Chungnam National University Hospitalwith spontaneous lobar ICH. We analyzed 75 patients. Excluded were no follow-up(8 patients) and patients died withinfew days(31 patients). All the patient was followed up at least two years aside from two patients who underwent epilepticseizure and died five and eight months later each. Medical history was obtained through medical record and by telephoneinterview. Statistical analyses were performed using Chi-square test, Student

Background
s and objective : EEG reflect dynamic changes of continuous neuronal activities by internal and externalstimuli. The aim of this study is to quantify nonlinearly the local dynamic differences among EEG data correspondingto different states of brain.Methods : EEG was recorded from twelve healthy normal subjects(mean age, 29.7 years; 8 men and 4 women) usingdigital EEG machine. 18-channel EEG data were selected during eyes closed(EC), eyes open(EO), and mental arithmetic(MA) in each subject. Correlation dimension(D2) and largest Lyapunov exponent(LLE) were calculated fromthree states and average value was mapped 2 dimensionally and compared with each other.Results : The distribution of D2 was relatively symmetric and its value was higher in frontal than in parieto-occipitalregion during EC. These findings were reversed during EO. Bilateral centro-temporo-parietal region showed high D2value in MA compared with those in EC, which was more prominent in left side. LLE was larger than zero in all stateand showed significant differences among EC, EO and MA(p=0.000).Conclusion : These results suggest that nonlinear analysis of EEG can quantify dynamic state of brain.

Background
: We studied EEG changes during pilocarpine-induced status epilepticus(SE), a widely used model whose EEG characteristics have not been fully described previously. Method : Male Sprague-Dawley rats weighing 250-350 grams were used as subjects. SE was induced 5-7 days after placement of chronic epidural electrodes, using 360-380mg/Kg pilocarpine IP. Rats were observed with continuous EEG recording following pilocarpine injection until end of the SE episode. Results : SE occurred in 10/12 rats studied. SE began with a series of discrete seizures 11.1?.93 minutes after pilocarpine injection. 5.2?.71 seizures occurred over 10.9?.62 minutes, until the EEG converted to a waxing and waning pattern, during which the amplitude and frequency of epileptiform activity increased. After 1.4?.82 minutes, a pattern of continuous high amplitude rapid spiking was established. Continuous spiking continued for 3.4?.48 hours with a very gradual decline in amplitude and frequency, until periodic epileptiform discharges(PEDs) began to occur. The EEG consisted primarily of PEDs for another 7.4?.09 hours, until electrographic generalized seizures beganto occur. These continued for 5.8?.82 hours until death. Duration of SE was 17.0?.88 hours. Flat periods were a prominent feature during all EEG patterns in this model. Conclusion : EEG features distinctive in pilocarpine SE(but not unique to it) include flat periods during all patterns and resumption of continuous spiking episodes after the onset of PEDs. The sequence of discrete seizures to waxing and waning to continuous spiking to PEDs was identical to that which has been described in humans and other animal models.

Purpose
: The rapid development and wide popularity of Digital EEG(DEEG) is due to its convenience, accuracy and applicability for quantitative analysis. These advantages of DEEG make one hesitate to use analog EEG(AEEG). To assess the advantage of DEEG system utilizing AEEG(DAEEG) over conventional AEEG and the clinical applicability, a DAEEG system was developed and applied to animal model. Methods : Sprague-Dawley rat as status epilepticus model were used for collecting the EEG data. After four epidural electrodes were inserted and connected to 8-channel analog EEG(Nihon-kohden, japan), continous EEG monitoring via computer screen was done from two rats simultaneously. EEG signals through analog amplifier and filters were digitized at digital signal processor and stored in Window-based pentium personal computer. Digital data were sampled at a rate of 200 Hz and 12 bit of resolution. Acquisition software was able to carry out 'real-time view, sensitivity control and event marking' during continuous EEG monitoring. Digital data were stored on hard disk and backed-up on CD-ROM for off-line review. Review system consisted of off-line review, saving and printing out interesting segment ad annotation function. Results : This DAEEG system could utilize most major functions of DEEG sufficiently while making a use of an AEEG. It was easy to monitor continuously compared to conventional AEEG and to control sensitivity during ictal period. Marking the event such as a clinical seizure or during injection was less favorable than AEEG due to slowed processing speed of digital processor and central processing unit. Reviewing EEG data was convenient, but paging speed was slow. Storage and mangement of data was handy and economical. Conclusion : Relatively simple digital EEG system utilizing AEEG can be set-up at a laboratory level. It may be possible to make an application for clinical purposes.

Reflex epilepsies are distinct but not clealy understood clinical entity. Various cerebral activities induced by simple stimulation including visual, auditory, somatosensory, as well as diverse functional tasks such as reading, calculation, complex thinking are believed to be seizure-inducing factors. We experienced two patients whose seizure were readily precipitated by complex, streunuous thinking. Both patients was teen-aged boy at the onset of seizure(13, and 15 years of age each) with normal physical and mental growth. Although first seizure was precipitated by watching TV and playing puzzels in each patient, initial diganosis was idiopathic generalized epilepsy, possible juvenile myoclonic epilepsy(JME). For the first few years, seizures were infrequent but mostly precipitated by the tasks needs concentration such as playing computer games, decision-making, mathematics, reading, or during the examination. EEG revealed various thinking process including reading hard books, drawing complex figure, complex calculation induced epileptic discharges even if it usually needs certain period of concentration. Phenytoin, valproic acid, clonazepam, vigabatrin, and lamotrigine sometimes abated their seizures but none of these made them seizure-free. Complex reflex epilepsy induced by thinking was proposed to be a separate type of epilepsy or a variant of JME, Age, sex, stereotypic seizure-inducing factors, clinical course, and refractory epilepsies in these patients highly suggested this type of epilepsy as a variant of JME but its refractoriness and unique provocation still needs more speculation.