Natasha Maurits

Reference values of maximum isometric muscle force obtained in 270 children aged 4-16 years by hand-held dynamometry

Since muscle force and functional ability are not related linearly; maximum force can be reduced while functional ability is still maintained. For diagnostic and therapeutic reasons loss of muscle force should be detected as early and accurately as possible. Because of growth factors, maximum muscle force in children varies with age, which makes detection of force loss difficult. The purpose of this study was to establish reference values for muscle force in children aged 4-16 years, obtained by hand-held dynamometry in 11 muscle groups. In boys muscle force was predicted best by weight whereas in girls weight and age were best predictors. At age 14 boys become significantly stronger for nearly all tested muscle groups. These age-related reference values can be used to quantify muscle weakness in individual muscle groups in children aged 4-16 years and to evaluate the effects of therapy.

Admitting Acute Ischemic Stroke Patients to a Stroke Care Monitoring Unit Versus a Conventional Stroke Unit: A Randomized Pilot Study

Background and Purpose— Pathophysiological considerations and observational studies indicate that elevated body temperature, hypoxia, hypotension, and cardiac arrhythmias in the acute phase of ischemic stroke may aggravate brain damage and worsen outcome. Methods— Both units were organized with the same standard care and multidisciplinary approach to nursing and rehabilitation. A blinded observer assessed functional outcome at 3 months with the modified Rankin scale (mRS) and Barthel Index (BI). End points were (1) poor outcome, defined as either mRS ≥4 or BI <60 or the need for institutional care and (2) mortality. Results— Fifty-four patients meeting the inclusion criteria were randomized. The groups were well matched for baseline characteristics, stroke subtype, stroke severity, vascular risk factors, and prognostic factors. Poor outcome was seen in 7 (25.9%) patients in the SCMU group and in 13 (48.1%) in the SU group (P =0.16). Mortality was lower in the SCMU group than in the SU group (1 [3.7%] vs 7 [25.9%]; odds ratio, 0.11 [95% CI, 0.02 to 0.96], P =0.05). Conclusions— This pilot study suggests that admission of acute stroke patients to an SCMU may reduce mortality and poor outcome. A larger trial is required to confirm these findings.

A Brain-Wide Study of Age-Related Changes in Functional Connectivity

Aging affects functional connectivity between brain areas, however, a complete picture of how aging affects integration of information within and between functional networks is missing. We used complex network measures, derived from a brain-wide graph, to provide a comprehensive overview of age-related changes in functional connectivity. Functional connectivity in young and older participants was assessed during resting-state fMRI. The results show that aging has a large impact, not only on connectivity within functional networks but also on connectivity between the different functional networks in the brain. Brain networks in the elderly showed decreased modularity (less distinct functional networks) and decreased local efficiency. Connectivity decreased with age within networks supporting higher level cognitive functions, that is, within the default mode, cingulo-opercular and fronto-parietal control networks. Conversely, no changes in connectivity within the somatomotor and visual networks, networks implicated in primary information processing, were observed. Connectivity between these networks even increased with age. A brain-wide analysis approach of functional connectivity in the aging brain thus seems fundamental in understanding how age affects integration of information.

μ-Suppression during Action Observation and Execution Correlates with BOLD in Dorsal Premotor, Inferior Parietal, and SI Cortices

The discovery of mirror neurons in the monkey, that fire during both the execution and the observation of the same action, sparked great interest in studying the human equivalent. For over a decade, both functional magnetic resonance imaging (fMRI) and electroencephalography (EEG) have been used to quantify activity in the human mirror neuron system (MNS)—yet, little is still known about how fMRI and EEG measures of the MNS relate to each other. To test the frequent assumption that regions of the MNS as evidenced by fMRI are the origin of the suppression of the EEG μ-rhythm during both action execution and observation, we recorded EEG and BOLD-fMRI signals simultaneously while participants observed and executed actions. We found that the suppression of the μ-rhythm in EEG covaried with BOLD activity in typical MNS regions, inferior parietal lobe (IPL), dorsal premotor (dPM) and primary somatosensory cortex (BA2), during both action observation and execution. In contrast, in BA44, only nonoverlapping voxels correlated with μ-suppression during observation and execution. These findings provide direct support for the notion that μ-suppression is a valid indicator of MNS activity in BA2, IPL, and dPM, but argues against the idea that mirror neurons in BA44 are the prime source of μ-suppression. These results shed light on the neural basis of μ-suppression and provide a basis for integrating more closely the flourishing but often separate literatures on the MNS using fMRI and EEG.

Reduced Specificity of Functional Connectivity in the Aging Brain During Task Performance

The importance of studying connectivity in the aging brain is increasingly recognized. Recent studies have shown that connectivity within the default mode network is reduced with age and have demonstrated a clear relation of these changes with cognitive functioning. However, research on age‐related changes in other functional networks is sparse and mainly focused on prespecified functional networks. Using functional magnetic resonance imaging, we investigated age‐related changes in functional connectivity during a visual oddball task in a range of functional networks. It was found that compared with young participants, elderly showed a decrease in connectivity between areas belonging to the same functional network. This was found in the default mode network and the somatomotor network. Moreover, in all identified networks, elderly showed increased connectivity between areas within these networks and areas belonging to different functional networks. Decreased connectivity within functional networks was related to poorer cognitive functioning in elderly. The results were interpreted as a decrease in the specificity of functional networks in older participants. Hum Brain Mapp 35:319–330, 2014.

Does fetal endoscopic closure of the myelomeningocele prevent loss of neurologic function in spina bifida aperta

Background Spina bifida aperta (SBA) is associated with shuntdependent hydrocephalus and with meningomyelocele (MMC). Fetal endoscopic closure of the MMC may reduce shunt-dependency, but the benefit upon motor function in individual patients is still unclear. An increase in differentiated muscle ultrasound density (dMUD) provides an objective parameter for the extent of muscle damage caudal to the MMC. In this perspective, we aimed to compare dMUD and neurological function between SBA children treated by fetal endoscopic closure (fSBA) and by neonatal closure (nSBA) of the MMC.

Comparison of serum S-100 protein levels following stroke and traumatic brain injury

Temporal changes in serum S-100 protein levels were compared between patients with ischemic stroke, transient ischemic attack (TIA) and traumatic brain injury (TBI). In addition, S-100 levels were correlated with clinical severity and outcome. Measurements were done with a LIA-mat((R)) Sangtec((R)) 100 using an automated immunoluminometric assay. Serum S-100 was measured in 21 stroke patients, 18 TIA patients and ten TBI patients on days 1 (0-24 h), 2, 3, 4, 5 or 6 and 8 or 9. In a control group of 28 healthy volunteers one measurement was done. For the stroke and TIA patients, National Institutes of Health Stroke Scale (NIHSS) scores were obtained on admission and on day 10. For the TBI patients, Glasgow Coma Scale (GCS) scores were obtained on admission and Glasgow Outcome Scale (GOS) scores were obtained after 6 months. Changes in serum S-100 levels over the first 3 days were significantly different between stroke and TBI patients (P=0.014) and between stroke and TIA patients (P=0.006). Peak concentrations of S-100 were most often observed on day 3 or 4 after stroke and on day 1 or 2 after TBI. In the stroke patients individual S-100 peak levels correlated well with the NIHSS score on admission (r=0.58 P=0.014) and the change in NIHSS score between day 10 and day 1 (r=0.65, P=0. 005). In the TBI patients a good correlation between individual peak levels of S-100 and the GCS score on admission (r=-0.81, P=0.010) and the GOS score 6 months after the trauma was found (r=-0.87, P=0. 004). We conclude that there is a significant difference in temporal changes of S-100 levels between ischemic stroke and TBI patients. This suggests different pathophysiological mechanisms. The results of this study further confirm that peak levels of serum S-100 correlate with neurological deficit resulting from either stroke or TBI.

The influence of mental fatigue and motivation on neural network dynamics; an EEG coherence study

The purpose of the present study is to examine the effects of mental fatigue and motivation on neural network dynamics activated during task switching. Mental fatigue was induced by 2 h of continuous performance; after which subjects were motivated by using social comparison and monetary reward as motivating factors to perform well for an additional 20 min. EEG coherence was used as a measure of synchronization of brain activity. Electrodes of interest were identified using a data-driven pre-processing method (ten Caat, M., Lorist, M.M., Bezdan, E., Roerdink, J.B.T.M., Maurits, N.M., 2008a. High-density EEG coherence analysis using functional units applied to mental fatigue. J. Neurosci. Meth. 171, 271-278; ten Caat, M., Maurits, N.M. and Roerdink, J.B.T.M., 2008b. Data-driven visualization and group analysis of multichannel EEG coherence with functional units. IEEE T. Vis. Comp. Gr. 14, 756-771). Performance on repetition trials was faster and more accurate than on switch trials. EEG data revealed more pronounced, frequency specific fronto-parietal network activation in switch trials, while power density was higher in repetition trials. The effects of mental fatigue on power and coherence were widespread, and not limited to specific frequency bands. Moreover, these effects were independent of specific task manipulations. This increase in neuronal activity and stronger synchronization between neural networks did not result in more efficient performance; response speed decreased and the number of errors increased in fatigued subjects. A modulation of the dopamine system is proposed as a common mechanism underlying the observed the fatigue effects.

Relation between muscle and brain activity during isometric contractions of the first dorsal interosseus muscle

We studied the relationship between muscle activity (electromyography, EMG), force, and brain activity during isometric contractions of the index finger, on a group and individual level. Ten subjects contracted their right or left index finger at 5, 15, 30, 50, and 70% of their maximal force. Subjects received visual feedback of the produced force. We focused our analysis on brain activation that correlated with EMG. Brain activity of specific anatomical areas (region‐of‐interest analysis, ROI) was quantified and correlated with EMG activity. Furthermore, we tried to distinguish between brain areas in which activity was modulated by the amount of EMG and areas that were active during the task but in which the activity was not modulated. Therefore, we used two regressors simultaneously: (1) the produced EMG and (2) the task (a categorical regressor). As expected, activity in the motor areas (contralateral sensorimotor cortex, premotor areas, and ipsilateral cerebellum) strongly correlated with the amount of EMG. In contrast, activity in frontal and parietal areas (inferior part of the right precentral sulcus, ipsilateral supramarginal gyrus, bilateral inferior parietal lobule, bilateral putamen, and insular cortex) correlated with activation per se, independently of the amount of EMG. Activity in these areas was equal during contractions of the right or left index finger. We suppose that these areas are more involved in higher order motor processes during the preparatory phase or monitoring feedback mechanisms. Furthermore, our ROI analysis showed that muscle and brain activity strongly correlate in traditional motor areas, both at group and at subject level. Hum Brain Mapp, 2008.

The MesoDyn project: software for mesoscale chemical engineering

Abstract We describe a new class of phenomenological mesoscopic models to simulate the phase separation dynamics in three dimensional complex liquids, based on dynamic density functional methods. These models are generalizations of time-dependent Ginzburg–Landau models and contain a molecular description of the liquids in the free energy functional. Possible applications are in process industries (HIPS, paints, detergents, surfactants,…), petroleum industries (oil recovery), pharmaceutical industries (drug delivery) and consumer product industries (food processing, cosmetics). We show the results of the simulation of the microphase behaviour of aqueous PL64 solutions. The work described here was mainly done within ESPRIT research projects funded by the European Union.