Research

Interests

• Working Memory
• Attention
• Connectivity Measures

• Visual System
• EEG

Projects

• Dispositionelle Achtsamkeit, Emotionsdysregulation und Lebensqualität bei Multipler Sklerose

  A study that started as a simple student project but found its way into clinic

  Objective:

  Multiple Sclerosis is a common disease which from the medical as well as health psychological point of view isn’t fully understood. Fatigue is one of its most common symptoms. While trait mindfullness and emotion regulation have made their way into mindsets of multiple sclerosis, fatigue did not.

  Method:

  A cross-sectional online survey was conducted with the German items of the questionnaires EUROHIS-QUOL, Difficulties in Emotion Regulation Scale, Fatigue Severity Scale, Five Facet Mindfulness Questionnaire, Stress-Coping Inventory and the WHO-5. Mediation analyses were conducted in SPSS and Process.

  Results:

  107 particpitants diagnosed with MS (M/Alter = 45 Jahre, SD = 10.85, Min. = 21, Max. = 69) were included for analyses. Mediating effects were found for the relationship between trait mindfullness and quality of life with mediators social support and emotion regulation. Fatigue however did not have a significant effect on this relation.

  Conclusion:

  We confirmed the mediating effects in the relation between trait mindfullness and quality of life that were seen in previous studies. However, we were not able to frame fatigue in the existing model. To find further starting points for patient-centred treatment, we see a necessity to understand intrapersonal pathomechanisms in MS and to further develop the model of stress and coping in MS.

  Keywords: Multiple Sclerosis, Fatigue, Quality of Life

• Recover from vision loss in subacute stroke:

  Are there advantages of tDCS treatment?

  Background

  Although recovery processes in visual cortex are still controversial, there is some evidence of plastic reorganisation of neural tissue after occipital stroke seen in fMRI (Brodtmann et al., 2007, 2008, 2015, Dilks et al., 2007). Bola et al. investigated the importance of fronto-occipital network dynamics in visual processing and the effect of transcranial alternating current stimulation (tACS) on those networks and on the restoration of blindness after optic nerve damage (Bola et al., 2014). All investigations regarding stroke-treatment in visual system damage were carried out in chronic phase (Alber et al. 2015) although neuroplasticity after the neural damage is pronounced in the first weeks after the damage. Since transcranial direct current stimulation (tDCS) is considered to be safe even in acute and sub-acute phase, we conducted this study not only looking at behavioural data but rather investigating neurophysiological correlates in terms of dynamics in the time course of the first 6 months after the event.

   

  Aim:

  Uncover the effects of tDCS in subacute stroke patients.

   

  Question:

  Does tDCS show similar effects in stroke recovery than tACS and would it – employed in an earlier stage – show any advantages compared to tACS?

   

  Methods:

  In a randomized, sham-controlled, double-blind clinical trial, nineteen sub-acute stroke patients diagnosed with unilateral posterior cerebral artery ischemia were enrolled. Patients were randomized in a verum and a sham group controlled for age, gender, mean sensitivity (MS) in threshold perimetry. The groups underwent a baseline resting-state and checkerboard-VEP EEG recording, a tDCS sham or verum treatment, then another EEG post-treatment recording after ten days and a final follow-up recording after three months.

   

  Results:

  Mean sensitivity increased significantly after treatment but dropped after 3 months in both groups (see chart). We calculated absolute change of power (post-treatment – baseline, follow-up – post-treatment; see graph) in all frequency bands to compare the change between hemispheres, groups and again link them with the change in our outcome variables. Verum and sham group showed significant differences in absolute change from baseline to post-treatment in Delta (t₁₅=2.615, p=.020), Theta (t₁₅=2.483, p=.025) and low Alpha (t₁₅=2.457, p=.027), and from post-treatment to follow-up in low Alpha (t₁₂=-2.297, p=.040) and high Alpha (t₁₂=-2.449, p.031), but only in the intact side. In general, verum group increased in power, whereas sham group decreased in power. When we compared both hemispheres, only in sham group low Alpha (t₈=-2.809, p=.023) and high Alpha (t₈=-2.891, p=.020) decreased significantly more in intact than in damaged hemisphere.

  Conclusion: When looking at resting state EEG power analyses, it seems that neurophysiological changes appear after some time after the stroke. Possibly, specific training induces physiological changes which could be interpreted as compensational mechanisms of the intact hemisphere. tDCS could have some protective effect in terms of stabilizing alpha power (see difference between verum und sham at t2). At follow up there is no difference anymore. Probably longer stimulation might stabilize the seen effect (mean sensitivity and alpha drop to follow up stronger in verum than in sham).

• Certainty of uncertainty:

  Prestimulus prediction of perception in the damaged visual system

  Background: In near-threshold stimuli experiments researches were able to determine several pre-stimulus EEG oscillations being correlated to behavioral performance (Kundu et al., 2014; van Dijk, 2008, Weisz et al., 2014). In some of these studies the research was focused on pre-stimulus frequencies that find their correlates in cognitive discrimination such as high-alpha activity. But however there is a gap so far in investigation on the pre-stimulus differences between the healthy and damaged brain.

   

  Aim: We try to find pre-stimulus correlates for vision discrimination not only in the healthy but also in the damaged brain. Research showed that damaged areas of vision seem to have an ability to recover when being activated but still the mechanisms of the treatment’s effectiveness are for the most part still unknown. With this study we not only try to investigate the brain’s ability to compensate input from an insufficient sensual source but we also try to encourage further research in the field of pre-stimulus brain state.

   

  Question: Do patients suffering from vision loss show a different pre-stimulus cognitive brain state compared to healthy controls?

   

  Methods: We investigated 34 subjects’ (19 suffering from monocular partial vision loss of different aetiologies, 15 controls) visual fields for “intermediate vision”-areas which in healthy controls were found around the blind spot (graph 1). We performed a monocular visual discrimination task while recording EEG, presenting 180 stimuli in each of six spots of “intermediate” vision. Subjects were asked to respond by button press once they see a stimulus while fixating a central spot. As an ex-post threshold experiment we only performed further investigation on spots of a .6/.4 up to .4/.6 discrimination rate to distinguish a sensitive pre-stimulus brain state (graph 2). We analysed prestimulus spectral power amplitudes and network parameters over PLV, comparing hit and miss epochs as well as between patients and healthy controls.

   

  Results: Spectral analysis showed a nearly significant difference between hit and miss epochs in beta band for patients: With p=0.058 occipital beta amplitude was stronger in hit than miss epochs. Between groups, with p=0.056 delta amplitude reached a nearly significantly higher level in patients than in controls. In the PLV analysis strong differences between the groups of patients and controls could be found (graphs 3-7). Not only is delta connectivity significantly stronger over the patients’ whole cortices but also certain connections are found to be significantly stronger over the patients’ cortices. These can be found both, within groups and between conditions as well as between conditions and within groups.

   

  Conclusion: Our findings not only support the importance of pre-stimulus brain state for cognitive discrimination but also show that the brain has a certain ability to compensate malfunctioned input from sensual sources. The graph analysis in combination with the spectral analysis supports an idea of regional – such as beta oscillations – and global processes – such as delta oscillations – going hand in hand (Handel et al, 2009; Jensen at al., 2007; Knyazev et al., 2006; Knyazev, 2011; López-Azcárate et al., 2013; Schutter et al., 2004; Schutter et al., 2012; Zhang et al., 2013). Furthermore an impairment of sensual input can be compensated by strengthening these structures. We strongly encourage further pre-stimulus research in the field of brain damage to investigate the compensatory effects of brain plasticity.