Electroencephalographic Characteristics of Alcohol Dependent Patients: 3-Dimensional Source Localization

OBJECTIVES: The power spectral analysis of electroencephalogram has been widely used to reveal the pathophysiology of the alcoholic brain. However, the results were not consistent and the three dimensional study can be hardly found. The purpose of this study was to investigate characteristics of the three dimensional electroencephalographic (EEG) activity of alcohol dependent patients using standardized low resolution electromagnetic tomography (sLORETA). METHODS: The participants consisted of 30 alcohol dependent patients and 30 normal healthy controls. All the participants were males who had refrained from alcohol at least one month and were not taking any medications. Thirty two channel EEG data was collected in the resting state with eyes-closed condition during 30 seconds. The three dimensional data was compared between two groups using sLORETA for delta, theta, alpha, beta1, beta2, and beta3 frequency bands. RESULTS: sLORETA revealed significantly increased brain cortical activity in alpha, beta1, beta2, and beta3 bands each in alcohol dependent patients compared to normal controls. The voxels showing the maximum significance were in the left transverse temporal gyrus, left superior temporal gyrus, left anterior cingulate, and left fusiform gyrus in alpha, beta1, beta2, and beta3 bands respectively. CONCLUSIONS: These results suggest that chronic alcohol intake may cause neurophysiological changes in cerebral activity. Therefore, the measuring of EEG can be helpful in understanding the pathophysiology of cognitive impairements in alcohol dependence.

Magnetoencefalografía: mapeo de la dinámica espaciotemporal de la actividad neuronal / Magnetoencephalography: mapping the spatiotemporal dynamics of neuronal activity

La magnetoencefalografía es una técnica de neuroimagen no invasiva que mide, con gran exactitud temporal, los campos magnéticos en la superficie de la cabeza producidos por corrientes neuronales en regiones cerebrales. Esta técnica es sumamente útil en la investigación básica y clínica, porque además permite ubicar el origen de la actividad neural en el cerebro. En esta revisión se abordan aspectos básicos de la biofísica del método y se discuten los hallazgos sobre procesos como la percepción del habla, la atención auditiva y la integración de la información visual y auditiva, que son importantes en la investigación. Igualmente, se ilustran sus ventajas, sus limitaciones y las nuevas tendencias en la investigación con magnetoencefalografía.

Magnetoencephalography is a noninvasive imaging technique that measures the magnetic fields on the surface of the head --produced by neuronal currents in brain regions -- and provides highly accurate temporal information. Magnetoencephalography is extremely useful in basic and clinical research as it can also locate the sources of neural activity in the brain. This review chiefly approaches biophysics-related aspects of the method; findings are also discussed on issues such as speech perception, auditory attention and integration of visual-auditory information, which are quintessential in this type of research. Lastly, this review discusses the benefits and limitations of magnetoencephalography and outlines new trends in research with this technique.

Current source and digital demodulation technique in EIT system based on FPGA / 国际生物医学工程杂志

ObjectiveA general experiment platform of electrical impedance tomography(EIT) based on field programmable gate array(FPGA) was designed to meet the requirements of EIT digital measurement.A digital current source and the research on digital demodulation method was completed.MethodsFor construction of the experiment platform,DDS module,D/A and A/D interface module,digital demodulation module and RS-232 communication module were all integrated in one FPGA chip.ResultsThe source can provide multi-frequency excitation signals of 2 mA in the range of 6.1-390.6 kHz.The output impedance of the source was higher than 190 kΩ.Both the real and the virtual information of measured impedance could be extracted.ConclusionMeasurements based on bioimpedance-equivalent circuit model verified the validity of the platform.The research results of this paper provides a foundation for the construction of a practical EIT system.

Current Source Distribution of Periodic Lateralized Epileptiform Discharge: Comparison With Diffusion-Wighted MR Imaging in Viral Encephalitis

BACKGROUND: Periodic lateralized epileptiform discharges (PLEDs) are the main electroencephalograph (EEG) findings that imply the existence of acute or subacute structural lesions. The purpose of this study was to investigate the electrophysiologic characteristics of PLEDs by identifying the relationship between the current-source distribution (CSD) of PLEDs and the high signal intensity of diffusion-weighted magnetic resonance imaging (MRI; HSI-DWI) in viral encephalitis. METHODS: Six patients were enrolled. Twenty typical EEG, 1-s epochs, including the negative peak of the PLEDs, were averaged into an averaged-PLED (a-PLED). The CSD at the negative peak point of the a-PLED was located on the Talairach human brain map in each patient. The CSDs of the patients were compared with the anatomic locations of encephalitic lesions observed on diffusion-weighted MRI. RESULTS: In all patients, the locations with HSI-DWI were observed in the cortical areas. In two out of the six patients the locations of CSD and those of HSI-DWI were matched. In the other patients, they were partly matched. The matched areas were observed in the frontal, temporal, and parietal areas. The additional areas of CSD were in both insular areas, and those of HSI-DWI were in the frontal, temporal, parietal, and occipital areas. CONCLUSIONS: This study showed that the CSDs of PLEDs in viral encephalitis were mostly matched with the HSI-DWI in the cortical area of the frontal, temporal, and parietal areas. The cortical lesion itself in viral encephalitis may be part of the neural generator of PLEDs.

Age Differences of Quantitative Electroencephalography and Current Source Density / 신경정신의학

OBJECTIVES: Age-related differences of the brain have been obtained by various methods. This study was aimed to explore the changes of quantitative electroencephalography (qEEG) and their source localization in normal aging. METHODS: Thirty-seven healthy young adults (mean age 35.22+/-13.62 years) and thirty-nine cognitively-healthy elderly subjects (mean age 72.95+/-5.73 years) participated in the study. Resting-state EEGs were recorded while subjects were in a relaxed state. Relative qEEG powers of five frequency bands were analyzed for eye closed conditions: delta (1-3 Hz), theta (4-7 Hz), alpha (8-12 Hz), beta (13-25 Hz), and gamma (30-50 Hz). The standardized low resolution electromagnetic tomography (sLORETA) was used to identify the current source densities of each frequency band. RESULTS: The elderly group showed an increase of beta and gamma power while the reduction of delta, theta, and alpha power compared with the young group. Controlling education as a covariate, the beta power was positively correlated with age, while theta power was negatively correlated with age in all subjects. sLORETA revealed that elderly subjects had reduced current source density at the cingulate gyrus in the theta band, while increased current source densities at the frontal, parietal, insula, and limbic areas in the beta band compared with young adults. CONCLUSION: Our results suggested that qEEG could reflect normal aging. Cognitively healthy elderly subjects showed an increase of high-frequency power, while showing a reduction of low-frequency power. These functional implications were discussed.

Current-source Analysis of Interictal Spikes in a Patient With Ictal Crying

Ictal crying has been associated with ictal activities in the medial frontal or medial temporal area of the nondominant hemisphere. We applied current-source analysis to the interictal spikes of a patient with episodes of ictal crying without sad feelings, but fear sensation. The current sources were in the medial frontal area of both cerebral hemispheres, the temporal area and the posterior cingulate gyrus of the right hemisphere.

Distributed Current Source Analysis of Alpha-Frequency Band in Alpha Coma: Drug Intoxication versus Pontine Infarction

Alpha coma is a coma state with predominant alpha activities in electroencephalography. There are two different patterns of alpha coma, depending upon the distribution of alpha activity. The causes may vary with the distribution pattern. To clarify the difference in alpha-activity distribution, we conducted current-source analysis of the alpha-frequency band in two patients with alpha-coma caused by drug intoxication and pontine infarction, respectively. The current-source analysis of alpha-frequency bands may make it easier to distinguish the distribution patterns.

Currrent Source Analysis of Interictal Spikes in a Patient With Ictal Grimacing

Facial grimacing can be a manifestation of complex partial seizures from the temporal lobe. We observed a case of seizure with facial grimacing and partial loss of consciousness during an electroencephalography recording. The recording revealed interictal spikes on the left-sided inferior temporal electrodes and ictal discharges starting on the same electrodes. The current source appeared to be in the inferior and lateral temporal areas of the left cerebral hemisphere. These results show that it is possible to localize the current sources responsible for interictal spikes.

Current Source Analysis of Interictal Spikes in Two Patients With Gelastic Epilepsy-Hypothalamic Hamartoma Syndrome

BACKGROUND: Interictal spikes in gelastic epilepsy-hypothalamic hamartoma syndrome are mainly in the fronto-temporal area. Current source analysis of the interictal spikes has not been done enough. We tried the current source analysis in 2 patients with gelastic epilepsy-hypothalamic hamartoma syndrome using both of the discrete and distributed models. METHODS: Twenty 1 sec epochs including the negative peak of the spikes, were selected from one or two electroencephalographic recordings respectively in each patient. These 20 epochs were averaged into a single spike. The current dipole sources of the averaged spike were analyzed and located on a spherical head model. The current source density of the negative peak point of the averaged spike was located on the Talairach human brain map. RESULTS: The current dipole sources were in the right subcallosal gyrus, or the right or left anterior cingulate gyri. The current source density was distributed in the bilateral medial frontal area including the anterior cingulate gyri. CONCLUSIONS: The interictal spikes of patients with gelastic epilepsy-hypothalamic hamartoma syndrome may be generated by the current sources located in the bilateral medial frontal area.

Increased EEG Current-Source Density in the High Beta Frequency Band Induced by Levetiracetam Adjunctive Therapy in Refractory Partial Epilepsy

BACKGROUND AND PURPOSE: Levetiracetam (LEV) is an antiepileptic drug (AED) that has favorable effects on cognition. Although neuropsychological studies have demonstrated these favorable outcomes on cognition, there are few electrophysiologic data describing the functional changes exerted by LEV. The purpose of this study was to determine the effects of LEV adjunctive therapy on the current-source density (CSD) in the high beta frequency band (22-30 Hz) of EEG background activity in refractory partial epilepsy (RPE). METHODS: We conducted a 24-week, open-label, prospective study in 24 patients with RPE. Scalp electroencephalography and neuropsychological tests (NPTs) were conducted twice, once before the LEV trial and then again after 24 weeks of medication. RESULTS: The CSD in the 22-30 Hz band of EEG background activity increased in the bilateral anterior cingulate gyri, left parahippocampal gyrus, and a small area of the right anterior parahippocampal gyrus after the LEV trial. Neither seizure freedom nor the dosage increment of LEV elicited meaningful CSD changes. Verbal memory and executive function were improved after the 24-week LEV trial. CONCLUSIONS: To our knowledge, this is the first study to examine the changes in CSD induced by LEV adjunctive therapy in RPE patients. The CSD changes and NPT results suggest that LEV enhances the activities of the neuronal networks in the prefrontal cortex and left hippocampus.