Arie Weeren

Quantitative EEG in ischemic stroke : Correlation with functional status after 6 months

OBJECTIVE Stroke is a major cause of adult-onset disability and dependency. We investigated whether EEG parameters are of prognostic value for functional outcome 6 months after ischemic stroke. METHODS One-hundred and ten patients presenting with acute ischemic stroke and persistent neurological deficits at EEG recording were incrementally included. Clinical characteristics, volume of ischemia and EEG parameters were correlated with functional outcome assessed with the modified Rankin Scale (mRS) score. Predictive values for disability, dependency and death were calculated using receiver operating characteristic (ROC) curves and logistic regression modeling. RESULTS The EEG pairwise derived Brain Symmetry Index (pdBSI) and (delta+theta)/(alpha+beta) ratio (DTABR) were significantly correlated with the modified Rankin Scale (mRS) score at month 6 (Spearman ρ=0.46 and ρ=0.47, respectively, p<0.0005 for both). NIHSS (OR 1.15, 95% CI 1.04-1.27, p=0.005) and pdBSI (OR 4.07, 95% CI 1.32-12.58, p=0.015) were independently associated with disability 6 months after stroke. Dependency was independently indicated by NIHSS (OR 1.22, 95% CI 1.09-1.37, p<0.0005) and DTABR (OR 2.25, 95% CI 1.16-4.37, p=0.016). Six month mortality was independently indicated by age at stroke onset (OR 1.18, 95% CI 1.05-1.32, p=0.007), NIHSS (OR 1.11, 95% CI 1.03-1.21, p=0.009) and DTABR (OR 2.04, 95% CI 1.08-3.85, p=0.028). CONCLUSIONS EEG in the subacute setting of ischemic stroke may be of prognostic value for disability, dependency and death after 6 months. SIGNIFICANCE Early prognostication of functional outcome after stroke is relevant to efficient rehabilitation management to enhance recovery and minimize long-term disability.

Reproducibility and clinical relevance of quantitative EEG parameters in cerebral ischemia: A basic approach

OBJECTIVE To investigate reproducibility and clinical relevance of quantitative EEG parameters in ischemic cerebrovascular disease. METHODS EEG was recorded in 31 patients suffering from subacute ischemic cerebrovascular disease. Ten age-matched control subjects were included as a reference group. Intra-recording, intrarater and interrater reproducibility was calculated for standard EEG measures and for a pair wise derived Brain Symmetry Index (pdBSI). Correlations between EEG parameters, clinical status and volume of ischemia on diffusion weighted imaging (DWI) were calculated. RESULTS pdBSI was sensitive to asymmetry in the amplitude and frequency domain in a random white noise model and in a simulated sinusoidal model. Minimal Cronbach alpha for intra-recording, intra- and inter-rater reproducibility ranged between 0.95 and 0.99 for standard spectral parameters and between 0.96 and 0.99 for pdBSI. We found a significant difference in pdBSI between stroke patients and control or TIA (p=0.0003). pdBSI correlated significantly with NIH stroke scale at admission and DWI volume across different levels of stroke probability (Spearmans rho=0.64-0.70 and 0.79-0.84, respectively, p<0.00001 for both). CONCLUSIONS pdBSI displays high multilevel reproducibility and reliably discriminates between stroke and TIA patients or control subjects, and correlates significantly with clinical and radiological status. SIGNIFICANCE Based on this methodological analysis, reliable EEG parameters can be evaluated in a general stroke population for clinically relevant state and outcome measures.

Asymptotic analysis of linear feedback Nash equilibria in nonzero-sum linear-quadratic differential games

In this paper, we discuss nonzero-sum linear-quadratic differential games. For this kind of games, the Nash equilibria for different kinds of information structures were first studied by Starr and Ho. Most of the literature on the topic of nonzero-sum linear-quadratic differential games is concerned with games of fixed, finite duration; i.e., games are studied over a finite time horizon tf. In this paper, we study the behavior of feedback Nash equilibria for tf→∞.In the case of memoryless perfect-state information, we study the so-called feedback Nash equilibrium. Contrary to the open-loop case, we note that the coupled Riccati equations for the feedback Nash equilibrium are inherently nonlinear. Therefore, we limit the dynamic analysis to the scalar case. For the special case that all parameters are scalar, a detailed dynamical analysis is given for the quadratic system of coupled Riccati equations. We show that the asymptotic behavior of the solutions of the Riccati equations depends strongly on the specified terminal values. Finally, we show that, although the feedback Nash equilibrium over any fixed finite horizon is generically unique, there can exist several different feedback Nash equilibria in stationary strategies for the infinite-horizon problem, even when we restrict our attention to Nash equilibria that are stable in the dynamical sense.

Quantitative EEG in ischemic stroke: Correlation with infarct volume and functional status in posterior circulation and lacunar syndromes

OBJECTIVE The significant impact of stroke on health care results in an unmet need for efficient stroke care in resources limited environments. Practical, inexpensive and easy to obtain predictive EEG parameters have been suggested in anterior circulation syndromes. We investigated whether EEG parameters are of additional predictive value with regard to lesion volume and short-term functional outcome in lacunar (LACS) and posterior circulation (POCS) syndromes of presumed ischemic origin. METHODS Sixty (60) patients presenting with LACS or POCS were incrementally included. EEG parameters were correlated with volume of ischemia and functional status. Predictive values for definite stroke and unfavourable outcome were calculated using receiver operating characteristic (ROC) curves and logistic regression modelling. RESULTS The pairwise derived brain symmetry index (pdBSI) emerged as independent predictor for definite stroke in patients presenting with LACS and POCS (odds ratio (OR) 2.69, 95% confidence interval (CI) 1.24-5.82, p=0.012) and in patients with a National Institutes of Health Stroke Scale (NIHSS) score of 0 at EEG recording (OR 7.67, 95% CI 1.24-47.32, p=0.026). In ROC analysis, the (delta+theta)/(alpha+beta) ratio (DTABR) predicted unfavourable outcome at day 7 with an accuracy of 83% in LACS but not in POCS. In logistic regression, unfavourable outcome in LACS was predicted by nominal NIHSS with marginal significance (OR 1.84, 95% CI 1.00-3.37, p=0.05), while in categorical modelling, DTABR>2.4 displayed a statistically significant ominous odd ratio of 13.00 (95% CI 1.11-152.35, p=0.041) with identical predicted and observed values. CONCLUSIONS EEG may be of additional value by confirming or excluding definite stroke after resolution of symptoms in lacunar and posterior circulation syndromes of presumed ischemic origin and prognosticating short-term functional status in lacunar syndrome. SIGNIFICANCE These findings may have an impact on stroke care.

Additional value of quantitative EEG in acute anterior circulation syndrome of presumed ischemic origin.

OBJECTIVE The clinical course of acute stroke can be highly variable and for effective management outcome prediction needs to be refined. We investigated whether EEG parameters are of additional diagnostic and prognostic value in the early phase of acute ischemic anterior circulation stroke. METHODS Ninety-four patients presenting with acute anterior circulation syndrome (ACS) of presumed ischemic origin were incrementally included. Clinical characteristics were correlated with volume of ischemia and EEG parameters. Predictive values for definite stroke, early neurological deterioration, spontaneous early neurological improvement and death within 1 week after ACS were calculated using ROC curves and logistic regression modelling. RESULTS In patients with normal or near normal NIHSS score of 0 or 1, the pairwise derived brain symmetry index (pdBSI) was an independent predictor for definite stroke displaying an overall accuracy of 80%. Early neurological deterioration was independently predicted by pdBSI with a correct classification rate of 95%. In ROC analysis, death was predicted by pdBSI with overall accuracy of 97%. Spontaneous neurological improvement was independently predicted by the delta+theta/alpha+beta - ratio with overall accuracy of 75%. Small-vessel stroke was independently predicted by pdBSI with a correct classification rate of 92%. CONCLUSIONS EEG may be of prognostic value for spontaneous neurological improvement, early neurological deterioration and death in the acute setting of acute anterior circulation syndrome of presumed ischemic origin. SIGNIFICANCE These findings may have an impact on stroke care.

Technical communique: A result on output feedback linear quadratic control

In this note we consider the static output feedback linear quadratic control problem. We present both necessary and sufficient conditions under which this problem has a solution in case the involved cost depends only on the output and control variables. This result is used to present both necessary and sufficient conditions under which the corresponding linear quadratic differential game has a Nash equilibrium in case the players use static output feedback control. Another consequence of this result is that the conditions also provide sufficient conditions for the static output stabilizability problem. Of course, in case these conditions are not met this does not mean that the system is not stabilizable via static output feedback.

A Result on Output Feedback Linear Quadratic Control

In this note we consider the static output feedback linear quadratic control problem. We present both necessary and sufficient conditions under which this problem has a solution in case the involved cost depend only on the output and control variables. This result is used to present both necessary and sufficient conditions under which the corresponding linear quadratic differential game has a Nash equilibrium in case the players use static output feedback control.

Macroeconomic Policy Interaction under EMU: A Dynamic Game Approach

In this article, we study macroeconomic stabilization in the Economic and Monetary Union (EMU) using a dynamic game approach. With the aid of a stylized macroeconomic model, this article analyzes the transmission and interaction of national fiscal policies and monetary policy of the European Central Bank (ECB) in the EMU. A special focus is on the effects of labor market institutions in the participating countries and of the introduction of fiscal stringency criteria like those imposed in the Stability and Growth Pact.

Clustering by publication patterns of senior authors in the social sciences and humanities

This study uses cluster analysis as a tool for mapping diversity of publication patterns in the social sciences and humanities (SSH). By algorithmic clustering of 1828 senior authors affiliated with 16 disciplines at five universities in Flanders, Belgium, based on the similarity of their publication patterns during 2000–2011, we distinguish two broad publication styles, both of which are present within each discipline. We conclude that diversity in SSH publication patterns cuts across disciplinary boundaries. Cluster analysis shows promise for application in research evaluation for the SSH.

EEG in Silent Small Vessel Disease: sLORETA Mapping Reveals Cortical Sources of Vascular Cognitive Impairment No Dementia in the Default Mode Network

Introduction: Vascular cognitive impairment, no dementia (vCIND) is a prevalent and potentially preventable disorder. Clinical presof the small vessel subcortical subtype may be insidious and difficult to diagnose in the initial stage. We investigated electroencephalographic sources of subcortical vCIND in comparison to amnesic multidomain mild cognitive impairment (amdMCI) to determine the additional diagnostic value of quantitative electroencephalograhy (EEG) in this setting. Methods: Fifty-seven community residing patients with an uneventful central neurological history and first presentation of cognitive decline without dementia were included, 35 patients were diagnosed with vCIND and 22 with amdMCI. A cognitive control group, deliberately recruited from a cerebrovascular impaired cohort, consisted of cognitively healthy participants who experienced a fully recovered first ever transient ischemic attack (TIA) without clinical or magnetic resonance imaging evidence of stroke. From standard EEGs, the differences in standardized low-resolution brain electromagnetic tomography (sLORETA) sources were determined for the discrete frequency ranges 1–4 (delta), 4–8 (theta), 8–10.5 (alpha1), 10.5–13 (alpha2), 13–22 (beta1), and 22–30 (beta2) Hz. Results: In vCIND, a statistically significant decrease in parietooccipital alpha1 relative power current density compared with TIA and mild cognitive impairment patients was found. There was a significant decrease in frontal and parietooccipital beta1 relative power current density in vCIND compared with TIA patients. A significant increase in (pre) frontal delta relative power current density in vCIND compared with amdMCI was found as well. In amdMCI, delta relative power current density was significantly increased in the core limbic system. Discussion: Cortical sources of abnormal EEG activity in regions implicated in the default mode network are revealed by sLORETA at an early stage in vascular cognitive impairment. Mapping of parietooccipital alpha1, frontoparietooccipital beta1 and (pre) frontal delta loci in vCIND may reflect early executive and visuospatial dysfunction in this cohort. Standard EEG with sLORETA mapping might be an additional, noninvasive, and cost-effective tool in the diagnostic workup of patients presenting with a cognitive decline.