Does EEG (visual and quantitative) reflect mental impairment in subcortical vascular dementia?

The effects of white matter hyperintensities on MEG power spectra in population with mild cognitive impairment

Cerebrovascular disease is responsible for up to 20% of cases of dementia worldwide, but also it is a major comorbid contributor to the progression of other neurodegenerative diseases, like Alzheimer's disease. White matter hyperintensities (WMH) are the most prevalent imaging marker in cerebrovascular disease. The presence and progression of WMH in the brain have been associated with general cognitive impairment and the risk to develop all types of dementia. The aim of this piece of work is the assessment of brain functional differences in an MCI population based on the WMH volume. One-hundred and twenty-nine individuals with mild cognitive impairment (MCI) underwent a neuropsychological evaluation, MRI assessment (T1 and Flair), and MEG recordings (5 min of eyes closed resting state). Those participants were further classified into vascular MCI (vMCI; n = 61, mean age 75 ± 4 years, 35 females) or non-vascular MCI (nvMCI; n = 56, mean age 72 ± 5 years, 36 females) according to their WMH total volume, assessed with an automatic detection toolbox, LST (SPM12). We used a completely data-driven approach to evaluate the differences in the power spectra between the groups. Interestingly, three clusters emerged: One cluster with widespread larger theta power and two clusters located in both temporal regions with smaller beta power for vMCI compared to nvMCI. Those power signatures were also associated with cognitive performance and hippocampal volume. Early identification and classification of dementia pathogenesis is a crucially important goal for the search for more effective management approaches. These findings could help to understand and try to palliate the contribution of WMH to particular symptoms in mixed dementia progress.

Understanding brain function in vascular cognitive impairment and dementia with EEG and MEG: A systematic review

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Vascular Cognitive Impairment (VCI) is the second most prevalent dementia worldwide.

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Cerebrovascular disease is a major comorbid contributor to neurodegenerative diseases.

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VCI patients show specific spectral, connectivity and evoked responses patterns.

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Literature suggests that EEG-MEG might provide promising biomarkers for early VCI.

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Further neurophysiological research is needed for VCI subtypes differentiation.

Vascular Cognitive Impairment (VCI) is the second most prevalent dementia after Alzheimer’s Disease (AD), and cerebrovascular disease (CBVD) is a major comorbid contributor to the progression of most neurodegenerative diseases. Early differentiation of cognitive impairment is critical given both the high prevalence of CBVD, and that its risk factors are modifiable. The ability for electroencephalogram (EEG) and magnetoencephalogram (MEG) to detect changes in brain functioning for other dementias suggests that they may also be promising biomarkers for early VCI. The present systematic review aims to summarize the literature regarding electrophysiological patterns of mild and major VCI. Despite considerable heterogeneity in clinical definition and electrophysiological methodology, common patterns exist when comparing patients with VCI to healthy controls (HC) and patients with AD, though there is a low specificity when comparing between VCI subgroups. Similar to other dementias, slowed frequency patterns and disrupted inter- and intra-hemispheric connectivity are repeatedly reported for VCI patients, as well as longer latencies and smaller amplitudes in evoked responses. Further study is needed to fully establish MEG and EEG as clinically useful biomarkers, including a clear definition of VCI and standardized methodology, allowing for comparison across groups and consolidation of multicenter efforts.

The association between carotid blood flow and resting-state brain activity in patients with cerebrovascular diseases

Cerebral hypoperfusion impairs brain activity and leads to cognitive impairment. Left and right common carotid arteries (CCA) are the major source of cerebral blood supply. It remains unclear whether blood flow in both CCA contributes equally to brain activity. Here, CCA blood flow was evaluated using ultrasonography in 23 patients with cerebrovascular diseases. Resting-state brain activity and cognitive status were also assessed using magnetoencephalography and a cognitive subscale of the Functional Independence Measure, respectively, to explore the relationships between blood flow, functional brain activity, and cognitive status. Our findings indicated that there was an association between blood flow and resting-state brain activity, and between resting-state brain activity and cognitive status. However, blood flow was not significantly associated with cognitive status directly. Furthermore, blood velocity in the right CCA correlated with resting-state brain activity, but not with the resistance index. In contrast, the resistance index in the left CCA correlated with resting-state brain activity, but not with blood velocity. Our findings suggest that hypoperfusion is important in the right CCA, whereas cerebral microcirculation is important in the left CCA for brain activity. Hence, this asymmetry should be considered when designing appropriate therapeutic strategies.

EEG measures for clinical research in major vascular cognitive impairment: recommendations by an expert panel

Vascular contribution to cognitive impairment (VCI) and dementia is related to etiologies that may affect the neurophysiological mechanisms regulating brain arousal and generating electroencephalographic (EEG) activity. A multidisciplinary expert panel reviewed the clinical literature and reached consensus about the EEG measures consistently found as abnormal in VCI patients with dementia. As compared to cognitively unimpaired individuals, those VCI patients showed (1) smaller amplitude of resting state alpha (8-12 Hz) rhythms dominant in posterior regions; (2) widespread increases in amplitude of delta (< 4 Hz) and theta (4-8 Hz) rhythms; and (3) delayed N200/P300 peak latencies in averaged event-related potentials, especially during the detection of auditory rare target stimuli requiring participants' responses in "oddball" paradigms. The expert panel formulated the following recommendations: (1) the above EEG measures are not specific for VCI and should not be used for its diagnosis; (2) they may be considered as "neural synchronization" biomarkers to enlighten the relationships between features of the VCI-related cerebrovascular lesions and abnormalities in neurophysiological brain mechanisms; and (3) they may be tested in future clinical trials as prognostic biomarkers and endpoints of interventions aimed at normalizing background brain excitability and vigilance in wakefulness.

Higher white matter hyperintensity lesion load is associated with reduced long-range functional connectivity

Cerebral small vessel disease is a common disease in the older population and is recognized as a major risk factor for cognitive decline and stroke. Small vessel disease is considered a global brain disease impacting the integrity of neuronal networks resulting in disturbances of structural and functional connectivity. A core feature of cerebral small vessel disease commonly present on neuroimaging is white matter hyperintensities. We studied high-resolution resting-state EEG, leveraging source reconstruction methods, in 35 participants with varying degree of white matter hyperintensities without clinically evident cognitive impairment in an observational study. In patients with increasing white matter lesion load, global theta power was increased independently of age. Whole-brain functional connectivity revealed a disrupted network confined to the alpha band in participants with higher white matter hyperintensities lesion load. The decrease of functional connectivity was evident in long-range connections, mostly originating or terminating in the frontal lobe. Cognitive testing revealed no global cognitive impairment; however, some participants revealed deficits of executive functions that were related to larger white matter hyperintensities lesion load. In summary, participants without clinical signs of mild cognitive impairment or dementia showed oscillatory changes that were significantly related to white matter lesion load. Hence, oscillatory neuronal network changes due to white matter lesions might act as biomarker prior to clinically relevant behavioural impairment.

Viral encephalitis in quantitative EEG

OBJECTIVE

Our aim was to study the character of quantitative EEG of viral encephalitis.

METHOD

Collect the EEG data of hospitalized children with viral encephalitis diagnosed by pediatricians from January 2013 to September 2016, and EEG data of normal cases at the same age were control group. Using quantitative EEG analysis technologies to obtain power spectrum value, power spectrum value, 1 power spectrum value, 12 power spectrum value, 21 power spectrum value, and 12 power spectrum value. Relative power spectrum values of 2 and were obtained by calculation. All the cases were divided into 5 groups according to the EEG character: age 3 group, age 4 group, age 5-6 group, age 7-9-year group, and age 10-14-year group. Viral encephalitis group and normal cases group were statistically compared to obtain characters of quantitative EEG with viral encephalitis.

RESULTS

Power spectrum values and power spectrum values of 3-14-year-old cases with encephalitis increased. 1 power spectrum values existed in age 3 group with viral encephalitis and declined at the post-head lead, while 11 and 12 power spectrum values existed in age 4-14 group with viral encephalitis declined at the post-head lead. The value of 2 Power spectrum values of age 3-9 group was limited in diagnosing viral encephalitis. 1 and 12 power spectrum values decrease in age 10-14 group with viral encephalitis. Relative power spectrum values of 2 and increased in age 3-14 group with viral encephalitis; Relative power spectrum values of decreased in age 3-14 group with viral encephalitis, most lead of relative power spectrum decreased in age 3-14 group with viral encephalitis.

CONCLUSION

The character of quantitative EEG of cases with viral encephalitis is similar to EEG, but more detailed, more precise, more intuitive and can be used for clinical diagnose of viral encephalitis.

Subclinical white matter lesions and medial temporal lobe atrophy are associated with EEG slowing in a memory clinic cohort

OBJECTIVE

The aim of the study was to describe the relationship between electroencephalographic (EEG) findings obtained by standardized visual analysis, subclinical white matter lesions (WML) and brain atrophy in a large memory clinic population.

METHODS

Patients with Alzheimer's disease (AD, n=58), mild cognitive impairment (MCI, n=141), subjective cognitive impairment (SCI, n=194) had clinical, MRI based WML severity and regional atrophy assessments, and routine resting EEG recording. Background activity (BA) and episodic and continuous abnormalities were assessed visually in EEG.

RESULTS

WML (p=0.006) and atrophy in medial temporal regions (MTA) (p=<0.001) were associated with slower BA in all diagnoses. WML were associated in SCI with total episodic EEG abnormalities (p=0.03).

CONCLUSIONS

EEG is associated with subclinical WML burden and cortical brain atrophy in a memory clinic population.

SIGNIFICANCE

Even the standard visually assessed EEG can complement a memory clinic diagnostic workup.

[French guidelines on electroencephalogram]

Electroencephalography allows the functional analysis of electrical brain cortical activity and is the gold standard for analyzing electrophysiological processes involved in epilepsy but also in several other dysfunctions of the central nervous system. Morphological imaging yields complementary data, yet it cannot replace the essential functional analysis tool that is EEG. Furthermore, EEG has the great advantage of being non-invasive, easy to perform and allows control tests when follow-up is necessary, even at the patient's bedside. Faced with the advances in knowledge, techniques and indications, the Société de Neurophysiologie Clinique de Langue Française (SNCLF) and the Ligue Française Contre l'Épilepsie (LFCE) found it necessary to provide an update on EEG recommendations. This article will review the methodology applied to this work, refine the various topics detailed in the following chapters. It will go over the summary of recommendations for each of these chapters and underline proposals for writing an EEG report. Some questions could not be answered by the review of the literature; in those cases, an expert advice was given by the working and reading groups in addition to the guidelines.

The diagnostic utility of EEG in early-onset dementia: a systematic review of the literature with narrative analysis

Early-onset dementia (EOD) is characterized by functionally impairing deterioration in memory, language, personality or visuospatial skills emerging under the age of 65. Cerebral functioning can be assessed by visual electroencephalography (EEG) interpretation. The aim of this systematic review is to evaluate the diagnostic utility of visual EEG in EOD focusing on Alzheimer's disease (AD), vascular dementia (VAD), dementia with Lewy bodies (DLB), and frontotemporal dementia (FTD). Medline, Embase, Scopus, Web of Knowledge, and Google Scholar were systematically searched for studies where EEGs were included in the diagnostic evaluation of patients with dementia under the age of 65. Each paper was quality assessed and the results grouped according to dementia cause with a narrative summary. 4,157 papers were screened, 12 studies met the eligibility criteria with a total of 965 patients. An abnormal EEG was common to all causes of EOD. EEG abnormalities are more severe in early-onset AD patients. EEG severity grade is independent of disease duration. Slow wave activity is common to all dementias, but is most prominent in DLB. Frontal intermittent rhythmic delta activity could be considered as supportive for the diagnosis of DLB as can a Grand Total EEG score of over 9.5. EEG is usually normal in FTD. Focal changes can be seen in advanced VAD. Studies employed small patient groups, varying diagnostic criteria, and only a minority of patient diagnoses was pathologically confirmed. EEG may be useful as an adjunct in the diagnosis of DLB and AD. Further prospective well-powered studies are required to investigate diagnostic utility more robustly.

Peak individual alpha frequency qualifies as a stable neurophysiological trait marker in healthy younger and older adults

The individual alpha frequency (IAF) of the human EEG reflects systemic properties of the brain, is highly heritable, and relates to cognitive functioning. Not much is known about the modifiability of IAF by cognitive interventions. We report analyses of resting EEG from a large-scale training study in which healthy younger (20-31 years, N = 30) and older (65-80 years, N = 28) adults practiced 12 cognitive tasks for ∼100 1-h sessions. EEG was recorded before and after the cognitive training intervention. In both age groups, IAF (and, in a control analysis, alpha amplitude) did not change, despite large gains in cognitive performance. As within-session reliability and test-retest stability were high for both age groups, imprecise measurements cannot account for the findings. In sum, IAF is highly stable in healthy adults up to 80 years, not easily modifiable by cognitive interventions alone, and thus qualifies as a stable neurophysiological trait marker.

Disturbed oscillatory brain dynamics in subcortical ischemic vascular dementia

Background

White matter hyperintensities (WMH) can lead to dementia but the underlying physiological mechanisms are unclear. We compared relative oscillatory power from electroencephalographic studies (EEGs) of 17 patients with subcortical ischemic vascular dementia, based on extensive white matter hyperintensities (SIVD-WMH) with 17 controls to investigate physiological changes underlying this diagnosis.

Results

Differences between the groups were large, with a decrease of relative power of fast activity in patients (alpha power 0.25 ± 0.12 versus 0.38 ± 0.13, p = 0.01; beta power 0.08 ± 0.04 versus 0.19 ± 0.07; p<0.001) and an increase in relative powers of slow activity in patients (theta power 0.32 ± 0.11 versus 0.14 ± 0.09; p<0.001 and delta power 0.31 ± 0.14 versus 0.23 ± 0.09; p<0.05). Lower relative beta power was related to worse cognitive performance in a linear regression analysis (standardized beta = 0.67, p<0.01).

Conclusions

This pattern of disturbance in oscillatory brain activity indicate loss of connections between neurons, providing a first step in the understanding of cognitive dysfunction in SIVD-WMH.

Slowing of EEG correlates with CSF biomarkers and reduced cognitive speed in elderly with normal cognition over 4 years

BACKGROUND

Cerebrospinal fluid (CSF) biomarkers and quantitative EEG show particular patterns of change in Alzheimer's disease (AD) and reflect neuropathologic processes and cerebral function, respectively. The changes precede cognitive decline and should be visible already in preclinical stages. We therefore aimed to investigate their relationship in cognitively healthy individuals.

METHOD

Thirty-three (33) elderly individuals with repeated normal scores on cognitive tests over 4.5 years underwent EEG recording with quantitative frequency analysis and analysis of CSF total tau (T-tau), phosphorylated tau (P-tau) and beta-amyloid(1-42) (Abeta42).

RESULTS

CSF T-tau and P-tau correlated with relative EEG theta power (r(s)>0.545; p<0.01), but not with relative alpha, beta or delta power. The combined P-tau/Abeta42 ratio exhibited an even stronger correlation with relative theta power (r(s)=0.622; p<0.001), especially in the right posterior quadrant of the head (r(s)=0.643; p<10(-4)). Slowing of cognitive speed correlated with increased relative theta power, foremost in the posterior quadrants (r(s)>0.503; p<0.01), and high P-tau/Abeta42 ratio (r(s)>0.462; p<0.01).

CONCLUSIONS

Our results suggest that already in cognitively healthy elderly subjects, biochemical changes in CSF, and the possible underlying neuropathologic processes it reflects, have an effect on cerebral function as visualized by the EEG rhythm and cognitive speed. It hereby suggests that CSF biomarkers and EEG theta activity might indicate early abnormal degenerative changes in the brain.