David M.A. Mehler

David M.A. Mehler
RWTH Aachen University

MD PhD
Junior group leader at RWTH Aachen University

About

53
Publications
24,205
Reads
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1,031
Citations
Introduction
I am a physician scientist (MD/PhD) focusing on neuroimaging and rehabilitation in Neurology and Psychiatry. My PhD focused on fMRI-neurofeedback in motor rehabilitation and depression at Cardiff University Brain Imaging Centre. My MD (Dr. med.) focused on studying motor learning in redundancy using a robotic manipulandum at University College London. Where possible I provide Open Access to my research materials, data and code: https://osf.io/feg4j/
Additional affiliations
August 2018 - August 2021
University of Münster
Position
  • PostDoc Position
October 2014 - October 2018
Cardiff University
Position
  • PhD, MD candidate
September 2012 - October 2013
University College London
Position
  • Researcher

Publications

Publications (53)
Preprint
Full-text available
Significance: The expansion of fNIRS methodology and analysis tools give rise to various design and analytical decisions researchers have to make. Several recent efforts have developed guidelines for preprocessing, analyzing, and reporting practices. For the planning stage of fNIRS studies, similar guidance would be desirable. Study preregistration...
Preprint
Full-text available
This preregistration template guides researchers who wish to preregister their EEG projects, more specifically studies investigating event-related potentials (ERPs) in the sensor space.
Preprint
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Machine learning (ML) techniques have gained popularity in the neuroimaging field due to their potential for classifying neuropsychiatric disorders based on brain patterns. However, the diagnostic predictive power of the existing algorithms has been limited by small sample sizes, lack of representativeness, data leakage, and/or overfitting. Here, w...
Article
Full-text available
Purpose: Motor symptoms of patients suffering from Parkinson’s disease (PD) are currently mainly treated with dopaminergic pharmacology, and where indicated, with deep brain stimulation. In the last decades, a substantial body of literature has described neurophysiological correlates related to both motor symptoms and treatment effects. These mecha...
Article
Full-text available
Neuroanatomical abnormalities have been reported along a continuum from at-risk stages, including high schizotypy, to early and chronic psychosis. However, a comprehensive neuroanatomical mapping of schizotypy remains to be established. The authors conducted the first large-scale meta-analyses of cortical and subcortical morphometric patterns of sc...
Preprint
Full-text available
Background Retrospective self-reports of childhood maltreatment are widely used in research and clinical practice. However, their validity has been questioned due to potential depressive bias. Yet, systematic investigations of this matter are sparse. Thus, we investigate if and to what extent retrospective maltreatment reports vary in relation to l...
Article
Full-text available
Early career researchers (ECRs) are faced with a range of competing pressures in academia, making self-management key to building a successful career. The Organization for Human Brain Mapping undertook a group effort to gather helpful advice for ECRs in self-management. Bielczyk et al.
Article
Full-text available
Dementia describes a set of symptoms that occur in neurodegenerative disorders and that is characterized by gradual loss of cognitive and behavioral functions. Recently, non-invasive neurofeedback training has been explored as a potential complementary treatment for patients suffering from dementia or mild cognitive impairment. Here we systematical...
Article
Full-text available
We currently observe a disconcerting phenomenon in machine learning studies in psychiatry: While we would expect larger samples to yield better results due to the availability of more data, larger machine learning studies consistently show much weaker performance than the numerous small-scale studies. Here, we systematically investigated this effec...
Preprint
Full-text available
Neuroanatomical abnormalities have been reported along a continuum from at-risk stages, including high schizotypy, to early and chronic psychosis. However, a comprehensive neuroanatomical mapping of schizotypy remains to be established. The authors conducted the first large-scale meta-analyses of cortical and subcortical morphometric patterns of sc...
Preprint
Full-text available
Dementia describes a set of symptoms that occur in neurodegenerative disorders and that is characterized by gradual loss of cognitive and behavioral functions. Recently, non-invasive neurofeedback training has been explored as a potential complementary treatment for patients suffering from dementia or mild cognitive impairment. Here we systematical...
Article
Background Major depressive disorder (MDD) and type 2 diabetes (T2D) are known to share clinical comorbidity and to have genetic overlap. Besides their shared genetics, both diseases seem to be associated with alterations in brain structural connectivity and impaired cognitive performance, but little is known about the mechanisms by which genetic r...
Preprint
Background: Non-invasive neurofeedback training is currently explored as a potential add-on therapy to treat patients suffering from major depressive disorder, and first trials show promising clin-ical effects. The temporal evolution of therapeutic change, however, remains unclear. Methods: Profile of mood states (POMS) questionnaire ratings were c...
Preprint
Increased appetite and body weight are core features of atypical depression. While previous research has consistently highlighted the presence of distinct immunometabolic profiles in atypical depression, little is still known about the neural correlates of atypical symptoms in major depression. Even though obesity and increased body-mass index have...
Article
Major depressive disorder (MDD) is the leading cause of disability worldwide. Neurofeedback training has been suggested as a potential additional treatment option for MDD patients not reaching remission from standard care (i.e., psychopharmacology and psychotherapy). Here we systematically reviewed neurofeedback studies employing electroencephalogr...
Article
Full-text available
These authors contributed equally to this work. All other authors are listed in reverse alphabetical order. Neurofeedback has begun to attract the attention and scrutiny of the scientific and medical mainstream. Here, neurofeedback researchers present a consensus-derived checklist that aims to improve the reporting and experimental design standards...
Preprint
Major depressive disorder (MDD) is the leading cause of disability worldwide. Neurofeedback training has been suggested as a potential additional treatment option for MDD patients not reaching remission from psychopharmacology and psychotherapy. Here we systematically reviewed neurofeedback studies employing electroencephalography, or functional ma...
Article
Full-text available
Background: The effects of electroencephalography (EEG) and functional magnetic resonance imaging (fMRI)-neurofeedback on brain activation and behaviors have been studied extensively in the past. More recently, researchers have begun to investigate the effects of functional near-infrared spectroscopy-based neurofeedback (fNIRS-neurofeedback). FNIRS...
Article
Full-text available
Ischemic stroke of the middle cerebral artery (MCA), a major brain vessel that supplies the primary motor and premotor cortex, is one of the most common causes for severe upper limb impairment. Currently available motor rehabilitation training largely lacks satisfying efficacy with over 70% of stroke survivors showing residual upper limb dysfunctio...
Article
Full-text available
A key objective in the field of translational psychiatry over the past few decades has been to identify the brain correlates of major depressive disorder (MDD). Identifying measurable indicators of brain processes associated with MDD could facilitate the detection of individuals at risk, and the development of novel treatments, the monitoring of tr...
Article
Early career researchers (ECRs) are faced with a range of competing pressures in academia, making self-management key to building a successful career. The Organization for Human Brain Mapping undertook a group effort to gather helpful advice for ECRs in self-management.
Article
Full-text available
Background: MD-PhD programmes throughout the world provide a platform for medical trainees to commit to a physician-scientist career, qualifying with both a medical degree (MD or equivalent) and Doctor of Philosophy (PhD). However, there are limited studies assessing the characteristics of MD-PhD programmes in Europe and the outcomes of MD-PhD stu...
Article
Full-text available
The organising principle of human motor cortex does not follow an anatomical body map, but rather a distributed representational structure in which motor primitives are com- bined to produce motor outputs. Electrophysiological recordings in primates and human imaging data suggest that M1 encodes kinematic features of movements, such as joint positi...
Article
Full-text available
Neurofeedback has begun to attract the attention and scrutiny of the scientific and medical mainstream. Here, neurofeedback researchers present a consensus-derived checklist that aims to improve the reporting and experimental design standards in the field.
Preprint
Full-text available
Background: The effects of electroencephalography (EEG)- and functional magnetic resonance imaging (fMRI)-neurofeedback on brain-activation, and behaviors have been studied extensively in the past. More recently, researchers have begun to investigate the effects of functional near-infrared spectroscopy-based neurofeedback (fNIRS-neurofeedback). FNI...
Preprint
Full-text available
We currently observe a disconcerting phenomenon in machine learning studies in psychiatry: While we would expect larger samples to yield better results due to the availability of more data, larger machine learning studies consistently show much weaker performance than the numerous small-scale studies. Here, we systematically investigated this effec...
Article
Full-text available
[This corrects the article DOI: 10.1371/journal.pbio.3000246.].
Preprint
Full-text available
A key objective in the field of translational psychiatry over the past few decades has been to identify the brain correlates common to individuals with major depressive disorder (MDD). Identifying measurable indicators of brain processes associated with MDD could facilitate the detection of individuals at risk, and the development of novel treatmen...
Article
Full-text available
Hypothesis tests for which the null hypothesis cannot be rejected ("null findings") are often seen as negative outcomes in psychology. Null findings can, however, bear important insights about the validity of theories and hypotheses. In addition, the tendency to publish mainly significant findings is considered a key reason for failures to replicat...
Article
Full-text available
Statistical hypothesis tests for which the null hypothesis cannot be rejected ("null findings") are often seen as negative outcomes in the life and social sciences and are thus scarcely published. Null findings can, however, bear important insights about the validity of theories and hypotheses. In fact, the tendency to publish mainly significant fi...
Article
Full-text available
The movement towards open science is a consequence of seemingly pervasive failures to replicate previous research. This transition comes with great benefits but also significant challenges that are likely to affect those who carry out the research, usually early career researchers (ECRs). Here, we describe key benefits, including reputational gains...
Preprint
Full-text available
Hand movements are controlled by neuronal networks in primary motor cortex (M1). The organising principle encoding hand movements in M1 does not follow an anatomical body map, but rather a distributed representational structure in which motor primitives are combined to produce motor outputs. Electrophysiological recordings in primates suggest that...
Chapter
Many scientific disciplines including medicine and psychology currently face a replication challenge: researchers who repeat published experiments fail to find results similar to those previously being reported. Failed replications thus imperil the credibility science and those who carry it out. We will review some bad practices that have led to fa...
Article
Transparent communication of research is key to foster understanding within and beyond the scientific community. An increased focus on reporting effect sizes in addition of p-value based significance statements or Bayes Factors may improve scientific communication with the general public. Across three studies (N = 652), we compared subjective infor...
Preprint
Full-text available
This checklist is intended to encourage robust experimental design and clear reporting for clinical and cognitive-behavioural neurofeedback experiments.
Preprint
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This checklist is intended to encourage robust experimental design and clear reporting for clinical and cognitive-behavioural neurofeedback experiments. Available at https://psyarxiv.com/nyx84
Preprint
Full-text available
As neuroscientists we want to understand how causal interactions or mechanisms within the brain give rise to perception, cognition, and behavior. It is typical to estimate interaction effects from measured activity using statistical techniques such as functional connectivity, Granger Causality,or information flow, whose outcomes are often falsely t...
Preprint
Full-text available
The movement towards open science is an unavoidable consequence of seemingly pervasive failures to replicate previous research. This transition comes with great benefits but also significant challenges that are likely to afflict those who carry out the research, usually Early Career Researchers (ECRs). Here, we describe key benefits including reput...
Article
Full-text available
There is increasing interest in exploring the use of functional MRI neurofeedback (fMRI-NF) as a therapeutic technique for a range of neurological conditions such as stroke and Parkinson's disease (PD). One main therapeutic potential of fMRI-NF is to enhance volitional control of damaged or dysfunctional neural nodes and networks via a closed-loop...
Article
Full-text available
Functional magnetic resonance imaging neurofeedback (fMRI-NF) training of areas involved in emotion processing can reduce depressive symptoms by over 40% on the Hamilton Depression Rating Scale (HDRS). However, it remains unclear if this efficacy is specific to feedback from emotion-regulating regions. We tested in a single-blind, randomised, contr...
Article
Full-text available
Statistical power is essential for robust science and replicability, but a meta-analysis by Button et al. in 2013 diagnosed a "power failure" for neuroscience. In contrast, Nord et al. (J Neurosci 37: 8051-8061, 2017) re-analyzed these data and suggested that some studies feature high power. We illustrate how publication and researcher bias might h...
Preprint
Full-text available
Transparent communication of research is key to foster understanding within and beyond the scientific community. Increased focus on reporting effect sizes in addition of p-value based significance statements may improve scientific communication with the general public. Across two studies (N = 446), we compared informativeness ratings for five effec...
Preprint
Full-text available
Transparent communication of research is key to foster understanding within and beyond the scientific community. Increased focus on reporting effect sizes in addition of p-value based significance statements may improve scientific communication with the general public. Across two studies (N = 446), we compared informativeness ratings for five effec...
Thesis
Neurofeedback training represents a form of biofeedback training with a history of over 50 years. During neurofeedback training participants aim to gain control over a feedback signal that represents the activity of a brain region or network of interest. As such, it holds promise for clinical translation as an add-on treatment for psychiatric and n...
Article
Full-text available
Reaching movements are comprised of the coordinated action across multiple joints. The human skeleton is redundant for this task because different joint configurations can lead to the same endpoint in space. How do people learn to use combinations of joints that maximize success in goal-directed motor tasks? To answer this question, we used a 3-deg...
Article
Full-text available
Objectives: Neurofeedback is a technique that aims to teach a subject to regulate a brain parameter measured by a technical interface to modulate his/her related brain and cognitive activities. However, the use of neurofeedback as a therapeutic tool for psychiatric disorders remains controversial. The aim of this review is to summarize and to comm...
Article
Full-text available
Dysphagia is a relevant symptom in Parkinson's disease, whose pathophysiology is poorly understood. It is mainly attributed to degeneration of brainstem nuclei. However, alterations in the cortical contribution to deglutition control in the course of Parkinson's disease have not been investigated. Here, we sought to determine the patterns of cortic...

Questions

Questions (3)
Question
Hello,
I am currently playing around with priors to decide which one makes most sense for the data I am expecting from an experiment that I want to preregister. My understanding about Cauchy priors is that they include larger effect sizes because of their heavy tails, whereas half normal does not. Here my questions:
1) I would have expected that a half normal is more sensitive to smaller effects compared to a Cauchy with default prior (0.707) because it puts no weight to these extreme effects. However, when I observe a relatively small effect, the Cauchy returns a larger BF than the half normal does, and vice versa when I observe a relatively large effect. Could someone explain this to me?
2) The Cauchy prior scaling "r" translates to 0.5 probability mass of effect sizes that one expects (e.g. for default r = 0.707, 50% fall in -0.707 to 0.707), whereas half normal priors are scaled by the (unstandardized) size of the effect under the alternative, (which is entered as the standard deviation of the distribution). Because of the shape of a normal, this thus should then translate to 0.68 probability mass?
3) Cauchy priors seems to be mostly used and I suppose this makes sense because they work in standardized (not native measurement units) and thus allow comparisons between studies. However, if a study acquires an internal validation measure against which learning effects can be compared, for example, it might make sense to test for effects using a (half) normal working with native units?
4) I guess one aspect to guide this decision is whether you are subjective or objective Bayesian. Besides this, is there anything else you think one should take into account?
Many thanks,
David
Question
Hello, 
 
We are currently piloting a simultaneoues EEG-fMRI experiment and struggle in particular with removing the BCG (cardioballistic) artefact. We have been using the latest version of BrainVision Analyzer so far and found the results to be not reliable.
If you have experience in removing such artefacts, I would be grateful for any advice regarding software that has implemented algorithms that work reliably.
Cheers,
David
Question
For multiple comparison correction of a whole brain analysis of patient fMRI data, I am wondering which technique of multiple comparison correction would be "more appropriate", RGF or Monte Carlo Simulation Cluster Thresholding?  From my understanding RGF is the more conservative approach. For a sample size n=32 (two groups, n=16 each) and an appropriate spatial smoothing kernel being used in the preprocessing, what in your opinion would be the "more" appropriate multiple comparison correction method? What are the pros and cons?  Cheers!

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