Evolution of cerebral edema and its relationship with power in the theta band

The focused quantitative EEG bio-marker in studying childhood atrophic encephalopathy

Although it is a normal involution process in advanced age, brain atrophy—also termed atrophic encephalopathy—can also occur prematurely in childhood as a consequential effect of brain tissues injury through trauma or central nervous system infection, though in both normal and premature occurrences this condition always presents with loss of volume relative to the skull. A common tool for the functional study of brain activities is an electroencephalogram, but analyses of this have reportedly identified mismatches between qualitative and quantitative forms, particularly in the use of Delta-alpha ratio (DAR) indices, meaning that the values may be case dependent. The current study thus examines the value of Focused Occipital Beta-Alpha Ratio (FOBAR) as a modified biomarker for evaluating brain functional changes resulting from brain atrophy. This cross-sectional design study involves 260 patients under 18 years of age. Specifically, 207 patients with brain atrophy are compared with 53 control subjects with CT scan-proven normal brain volume. All the children underwent digital electroencephalography with brain mapping. Results show that alpha posterior dominant rhythm was present in 88 atrophic children and 44 controls. Beta as posterior dominant rhythm was present in an overwhelming 91.5% of atrophic subjects, with 0.009 p-values. The focused occipital Beta-alpha ratio correlated significantly with brain volume loss presented in diagonal brain fraction. The FOBAR and DAR values of the QEEG showed no significant correlation. This work concludes that QEEG cerebral dysfunctional studies may be etiologically and case dependent from the nature of the brain injury. Also, the focused Beta-alpha ratio of the QEEG is a prospective and potential biomarker of consideration in studying childhood atrophic encephalopathy.

The use of current source density as electrophysiological correlates in neuropsychiatric disorders: A review of human studies

The use of current source density (CSD), the Laplacian of the scalp surface voltage, to map the electrical activity of the brain is a powerful method in studies of cognitive and affective phenomena. During the last few decades, mapping of CSD has been successfully applied to characterize several neuropsychiatric conditions such as alcoholism, schizophrenia, depression, anxiety disorders, childhood/developmental disorders, and neurological conditions (i.e., epilepsy and brain lesions) using electrophysiological data from resting state and during cognitive performance. The use of CSD and Laplacian measures has proven effective in elucidating topographic and activation differences between groups: i) patients with a specific diagnosis vs. healthy controls, ii) subjects at high risk for a specific diagnosis vs. low risk or normal controls, and iii) patients with specific symptom(s) vs. patients without these symptom(s). The present review outlines and summarizes the studies that have employed CSD measures in investigating several neuropsychiatric conditions. The advantages and potential of CSD-based methods in clinical and research applications along with some of the limitations inherent in the CSD-based methods are discussed in the review, as well as future directions to expand the implementation of CSD to other potential clinical applications. As CSD methods have proved to be more advantageous than using scalp potential data to understand topographic and source activations, its clinical applications offer promising potential, not only for a better understanding of a range of psychiatric conditions, but also for a variety of focal neurological disorders, including epilepsy and other conditions involving brain lesions and surgical interventions.

Treatment-related changes in functional connectivity in brain tumor patients: a magnetoencephalography study

Widespread disturbances in resting state functional connectivity between remote brain areas have been demonstrated in patients with brain tumors. Functional connectivity has been associated with neurocognitive deficits in these patients. Thus far, it is unknown how (surgical) treatment affects functional connectivity. Functional connectivity before and after tumor resection was compared in primary brain tumor patients. Data from 15 newly diagnosed brain tumor patients were analyzed. Patients underwent tumor resection, and both preoperative (up to five months prior to surgery) and postoperative (up to ten months following surgery) resting state magnetoencephalography (MEG) recordings. Seven of the patients (47%) underwent radiotherapy after neurosurgery. Functional connectivity was assessed by the phase lag index (PLI), a measure of the correlation between MEG sensors that is not sensitive to volume conduction. PLIs were averaged to one short-distance and two long-distance (interhemispheric and intrahemispheric) scores in seven frequency bands. We found that functional connectivity changed in a complex manner after tumor resection, depending on frequency band and functional connectivity type. Post-hoc analyses yielded a significant decrease of interhemispheric PLI in the theta band after tumor resection. This result proved to be robust and was not influenced by radiotherapy or a variety of tumor- and patient-related factors.

QEEG prognostic value in acute stroke

The objective of our study is to determine the predictive value of QEEG in patients suffering from an acute ischemic cerebral stroke. Twenty-eight patients were studied within the first 72 hours of clinical evolution of middle cerebral artery territory ischemic stroke. Thirty-seven QEEG recordings were obtained: 13 in the first 24 hours after cerebral stroke onset, 9 between 24-48 hours and 15 between 48-72 hours. Absolute Energies (AE) were the QEEG selected variables for statistical analysis: first, AE Z values were calculated using the Cuban QEEG norms, then the maximum and minimum AE Z values were selected within each frequency band and total power. The medians of the five neighboring Z values were also chosen. Regression models were estimated using the RANKIN scores as dependent variables and the selected QEEG variables as independent, then outcome predictions at hospital discharge and 3 months later were calculated. Percentages of concordance and errors between the estimated and real outcome scores were obtained. Alpha and theta AE were the best predictor for short-term outcome and delta AE for long-term outcome. We conclude that QEEG performed within the first 72 hours of ischemic stroke might be a powerful tool predicting short- and long-term outcome.

Magnetoencephalographic analysis of cortical oscillatory activity in patients with brain tumors: Synthetic aperture magnetometry (SAM) functional imaging of delta band activity

Abnormal focal slow wave activity on electroencephalography and magnetoencephalography (MEG) is often seen in patients with various brain pathologies and MEG is capable of localizing cortical oscillatory activity with enhanced accuracy. In addition, MEG with synthetic aperture magnetometry (SAM) can depict changes in cortical oscillatory activity tomographically. Using SAM, we recorded cortical rhythms in patients with a brain tumor and evaluated the tomographic appearance of focal slow wave activity in relation to clinical signs and symptoms. Spontaneous MEG recordings were obtained in 15 patients with brain tumors. Statistically-determined power distributions in the delta-, theta-, and alpha-frequency bands were displayed tomographically and overlaid on individual magnetic resonance images. The location, strength and volume of enhanced activity were analyzed. Delta and theta band activities were significantly more intense in the cortex adjacent to tumors and in the surrounding edematous cortical areas than in other portions of the cortex. In 13 of the 15 patients, spatial distribution of enhanced focal delta activity coincided with the area responsible for the presenting signs and symptoms. Volumetric analysis revealed that emergence of tumor-related focal delta band activity in the cortex adjacent to a tumor, or with peritumoral edema, was greater for intra-axial tumors involving subcortical fibers than for extra-axial tumors. Patients with an increased volume of enhanced delta activity exhibited poor recovery of function in the early postoperative period. It is concluded that SAM imaging of focal delta activity can reveal functional alterations in cortical activity in patients with brain tumors and is useful for assessing cortical states associated with the existing pathology.

Rhythmic brain activity at rest from rolandic areas in acute mono-hemispheric stroke: a magnetoencephalographic study

In order to deepen our knowledge of the brain's ability to react to a cerebral insult, it is fundamental to obtain a "snapshot" of the acute phase, both for understanding the neural condition immediately after the insult and as a starting point for follow-up and clinical outcome prognosis. The characteristics of the brain's spontaneous neuronal activity in perirolandic cortical areas were investigated in 32 patients who had a stroke in the middle cerebral artery (MCA) territory of one hemisphere in the previous 10 days. Magnetic fields from both left and right rolandic areas were recorded at rest with open eyes. Total and band power properties, the individual alpha frequency (IAF) and the spectral entropy were analyzed and compared with a sex-age matched control group. In agreement with electroencephalographic literature, low frequency absolute powers were higher and high frequency were lower in the affected (AH) than in the unaffected hemisphere (UH), and also their values in both hemispheres differed from control values. An IAF reduction was found in AH with respect to UH. As new findings, the total power was higher in AH than in UH, after excluding 4 right-damaged patients with cortico-subcortical lesions, who showed a completely disorganized spectral pattern. Spectral entropy was lower in AH than in UH. Clinical severity correlated with the AH decrease of gamma band power, IAF and spectral entropy. Larger lesions were associated to worse clinical pictures and MEG alterations. A lesion affecting the MCA territory of one hemisphere induces a perilesional increase of the low-frequency rhythms' spectral power within the AH rolandic areas; the same effect was present also in the UH, indicating interhemispheric diaschisis. In the AH, results showed an increase of the total power and a reduction of the spectral entropy, suggesting a higher synchrony of local neuronal activity, a reduction of the intra-cortical inhibitory networks efficiency and an increase of neuronal excitability. Direct correlation linked gamma band activity preservation and less severe clinical status. Dependence of the clinical picture, and associated spectral alterations, on the lesion volume and not on the lesion level, suggests a diffuse neuronal impairment, rather than a selective structures damage, contributing to neurological status in the acute phase of stroke.

Variable resolution electromagnetic tomography (VARETA) in evaluation of compression of cerebral arteries due to deep midline brain lesions

BACKGROUND

Hemispheric tumors produced electroencephalographic (EEG) delta activity mainly due to deafferentation of cerebral cortex. In small, deep midline lesions that compressed cerebral arteries, the most important abnormality should have been in EEG theta band that selectively responded to brain ischemia. Frequency domain-variable resolution electromagnetic tomography (FD-VARETA) has been applied satisfactorily to the study of brain tumors, cerebral infarcts, and brain hemorrhages and was shown to localize areas of hypoperfusion.

METHODS

Twelve patients with deep midline lesions compressing different cerebral arteries were studied. Computer tomography (CT) and/or magnetic resonance imaging (MRI) as well as quantitative EEG with source calculation in frequency domain were obtained. Brain electromagnetic tomographies (BETs) were calculated to evaluate localization and extension of functional abnormalities.

RESULTS

Ten of twelve cases presented abnormal sources in theta band as main abnormal source. In only two cases was the main source in delta band, but these cases also had abnormal Z values in theta band. In four patients there were only abnormal values in theta range. Sources of abnormal theta activity were observed in regions irrigated by the arteries compressed.

CONCLUSIONS

In deep midline lesions, compression of cerebral arteries producing relative ischemia may explain abnormal EEG sources in theta band. Patients with main source in theta band showed vascular compression and some patients exhibited vasogenic edema. Thus, theta might be due to relative ischemia produced by both hypoperfusion and edema. Once again, VARETA has found to be very useful in evaluation of functional abnormalities.

Sources of abnormal EEG activity in spontaneous intracerebral hemorrhage

This report describes the results obtained with EEG source analysis in the frequency domain (FD-VARETA), in 14 patients with brain hemorrhages; 6 hemorrhages were located in the putaminal region, 1 was mesencephalic and 7 were lobar cerebral hemorrhages. Our goal was to evaluate FD-VARETA accuracy for the localization of fast growth expansive brain lesions. FD-VARETA produces brain electromagnetic tomography images of EEG sources in every frequency. The location of the most abnormal or the maximum Z value across all frequencies was compared with the location of spontaneous hemorrhages in computed tomographies (CT). In all patients the main source was within delta or theta bands. The spatial extent of the sources, in the brain atlas, at these frequency values was almost the same as the volume of hematoma in CT. Putaminal lesions produced larger regions of cortical deafferentation than lobar hematomas, with higher abnormal Z values. FD-VARETA was more accurate in locating the lesions than traditional maps of absolute and relative power in delta, theta, alpha and beta bands.

CONCLUSION

FD-VARETA is a valuable procedure for the functional evaluation of brain hemorrhages.

Cerebral blood flow and sources of abnormal EEG activity (VARETA) in neurocysticercosis

OBJECTIVES

To compare two different functional procedures in the assessment of brain ischemia in patients with neurocysticercosis (NCC): (1) electroencephalography (EEG) evaluated by brain maps and EEG current sources in the frequency domain using variable resolution electromagnetic tomography and (2) blood flow analyzed by computerized tomography assessed with stable Xe (Xe-CT).

METHODS

Eleven patients with NCC at different evolution stages were studied. CT and Xe-CT scans, as well as quantitative electroencephalography with source calculation in the frequency domain, were obtained. All patients showed cysts and in 6 of them there were also vascular complications: two of them presented calcifications of the middle cerebral artery, two other subjects showed calcifications of the vessels in the circle of Willis and the remaining two had brain infarctions.

RESULTS

In the cyst areas important hypoperfused zones were observed, as intense as those observed in infarcted areas. Damage to the blood-brain barrier was originated by parasites in colloidal phase (final cysticerci stage) producing large areas of edema and hypoperfusion. Abnormal delta EEG activity was observed in very large lesions, probably generated by partial cortical deafferentation; and abnormal theta activity was mainly related to the presence of edema.

CONCLUSIONS

Sources of abnormal EEG activity were very similar in topography to the hypoperfused areas.

Sources of abnormal EEG activity in brain infarctions

EEGs from 16 patients with stroke in three different stages of evolution were recorded. EEG sources were calculated every 0.39 Hz by frequency domain VARETA. The main source was within the delta band in 2 out of 4 chronic patients, and in 67% of the patients in the acute or subacute stages when edema (cytotoxic or vasogenic) was present. Moreover, all patients showed abnormal activity in the theta band. Sources of abnormal activity in cortical or corticosubcortical infarcts were located in the cortex, surrounding the lesion. At the site of the infarct, a decrease of EEG power was observed. Sources of abnormal theta power coincided with edema and/or ischemic penumbra.

Long-term intra-individual variability of the background EEG in normals

OBJECTIVES

Forty-five healthy adult volunteers underwent repeated qEEG examinations with retest intervals 25-62 months in order to investigate the long-term intra-individual variability of several qEEG features such as, absolute and relative power, power asymmetry, coherence, mean and peak frequency and entropy. Prior to any computations all parameters were transformed to Z-scores on the basis of a normal database.

METHODS

Correlation coefficients were used to test the effect of the time on the test-retest differences. Correlation coefficients were also computed between baseline and retest values, as a measure of intra-individual stability, to make our results comparable to most literature data. By computing the standard deviations for test-retest differences, the intra-individual variabilities of the examined parameters were obtained in the unit of inter-individual variability of normal population. The same calculations were carried out with values obtained from the odd and even numbered epochs of the same EEG sections. This way, that portion of the intra-individual variability was estimated that might be introduced even by chance only when the epochs were selected randomly from the same section of EEG conforming to selection criteria.

RESULTS

As for our results, further increase of test-retest differences with time after 25 months might be so insignificant that it could not be demonstrated in our test material. The long-term intra-individual variability for most parameters, especially for total absolute power and alpha mean frequency, was less than the inter-individual variability in the normal population. The moment-to-moment variability was least in the case of the absolute power.

CONCLUSIONS

Estimates for intra-individual variability expressed this way in Z-scores might easily be used in the follow-up of patients even for a few years.

Sources of abnormal EEG activity in the presence of brain lesions

In routine clinical EEG, a common origin is assumed for delta and theta rhythms produced by brain lesions. In previous papers, we have provided some experimental support, based on High Resolution qEEG and dipole fitting in the frequency domain, for the hypothesis that delta and theta spectral power have independent origins related to lesion and edema respectively. This paper describes the results obtained with Frequency Domain VARETA (FD-VARETA) in a group of 13 patients with cortical space-occupying lesions, in order to: 1) Test the accuracy of FD-VARETA for the localization of brain lesions, and 2) To provide further support for the independent origin of delta and theta components. FD VARETA is a distributed inverse solution, constrained by the Montreal Neurological Institute probabilistic atlas that estimates the spectra of EEG sources. In all patients, logarithmic transformed source spectra were compared with age-matched normative values, defining the Z source spectrum. Maximum Z values were found in 10 patients within the delta band (1.56 to 3.12 Hz); the spatial extent of these sources in the atlas corresponded with the location of the tumors in the CT. In 2 patients with small metastases and large volumes of edema and in a patient showing only edema, maximum Z values were found between 4.29 and 5.12 Hz. The spatial extent of the sources at these frequencies was within the volume of the edema in the CT. These results provided strong support to the hypothesis that both delta and theta abnormal EEG activities are the counterparts of two different pathophysiological processes.