Pitches and demonstrations:
- 8D Games – Maarten Stevens
- Basalt – Dick-Jan Zijda
- Motek – Frans Steenbrink
- InMotionVR – Patrick Faber
- TMSi – Leonie ter Stege & Joost Herijgers
Improved Classification of Chronic Pain Patients using a Random Forrest Classifier
Boudewijn van den Berg – University of Twente
Diagnosis and stratification of chronic pain patients is difficult due to a lack of sensitive biomarkers for altered nociceptive and pain processing. Recent developments enabled to preferentially stimulate epidermal nerve fibers and simultaneously quantify the psychophysical detection probability and neurophysiological EEG responses. In this work, we study whether using one or a combination of both outcome measures could aid in the observation of altered nociceptive processing and the classification of patients with chronic pain based on the outcomes. We used a random forest classifier to study whether psychophysical features, EEG features or a combination can improve the classification accuracy.
The impact of electrode interaction on the auditory processing of CI users
Elisabeth Noordanus – Radboud University
Cochlear implant (CI) users display a large variability in speech recognition in silence and – even more – in noise. Possible sources of this variability are multifold. These can be device-related, for example, 1) differences in the precise locations of CI electrodes in the cochlea, and 2) interference between electrodes because of overlapping auditory nerve populations, together with 3) suboptimal individual settings of the sound processor. Alternatively, or in addition, the cause of variability may be subject–related, for example 4) degeneration of the auditory nerve, 5) deficiencies in the more central auditory processing, or 6) cognitive factors. Currently, no methods are available to disentangle the influence of these six sources of variability on speech recognition. We investigate two new methods to determine the spectro-temporal resolution on electrode-level and take, in a controlled way, the impact of CI electrode interactions on the processing of temporal and spectral information into account, excluding influences of the sound processor (point 3) and largely excluding cognitive influences (point 6). Both new methods use direct stimulation of the CI electrodes, bypassing the sound processor. In our first experiments we stimulated two electrodes with the same pulse rate (1300 pps, in the clinical range), each with a different modulation frequency. One method measures with EEG the response to this known input, without any active involvement of the subject, the other detects the reaction time of the subject to a change in the modulation frequency of one of the electrodes or a change in stimulated electrode.
We tested the two new methods with 20 CI users. In addition, we used existing measurement methods to characterize the device (impedance measurements and Electrode Field Imaging) and the response of the auditory nerve (electrical Compound Action Potential and Spread of Excitation). Further, we determined the spectro-temporal performance also using the clinical sound processor and measured phoneme and speech recognition in noise. Preliminary analysis indicates that both new methods give relevant results. The interpretation of the results of the reaction time based method is more straightforward and the implementation of this method for clinical use is easier than that of the EEG based method. Further analysis will focus on the correlation of the results of the whole set of measurements, to relate outcomes of the new test methods to those of the device, the auditory nerve and to speech performance.
Non-individualized tES in chronic stroke patients leads to unpredictable stimulation of the motor hand area
Joris van der Cruijsen – Erasmus MC
“Transcranial electric stimulation (tES) is suggested to reduce functional impairments following stroke. However, reviews of tES on the motor system show minor and inconsistent effects. Interindividual differences in anatomy, stroke lesion location and size, and functional brain reorganisation after stroke may contribute to these inconsistent effects. Here, we investigated by simulation if variability in (lesion) anatomy and functional (re)organisation could explain tES effects in chronic stroke subjects.
In 21 chronic stroke patients and ten age-matched healthy controls, we used MRI to construct individualised FEM head models for tES simulation and analysed functional reorganisation using source localisation of HD-EEG recorded during a wrist manipulator task. We simulated conventional anodal transcranial direct current stimulation (tDCS; anode on C3 or C4; cathode on Fp1 or Fp2) in each subject. We extracted the normal component of the electric field (EN) in the contralateral motor hand knob and a functional target based on the source-localised EEG. Subsequently, we optimised the electrode locations to maximise the normal component of the electric field within these two targets.
Simulation of conventional anodal tDCS showed that EN varied between stroke subjects in the motor hand knob. The conventional electrode configuration resulted in both negative and positive electric fields, depending on anatomy and target location (median: 0.150 V/m range: -0.044 – 0.251 V/m) and in the functional target (median: 0.024 V/m range: -0.318 – 0.316 V/m). Stimulation intensity was lower in stroke patients compared to healthy subjects (z=2.179; p=0.029). Optimisation increased stimulation intensity for patients and healthy controls to similar levels (z=1.353; p=0.176).
In conclusion, we found that conventional anodal stimulation targeting the anatomical hand motor area or an EEG-based functional target is unsuitable for stroke patients. Therefore, an individualised optimisation of tES is required to prevent negligible or even opposite stimulation of the motor hand area.
Implementation of realistic electrode properties in forward volume conduction models
Meron Vermaas – Radboudumc
In applications like epilepsy treatment and brain-computer interfaces, electrocorticography (ECoG) electrode grids are often implanted in patients to detect normal and abnormal brain activity. In these applications, there is the need to assess the sensitivity of current or newly-designed ECoG grids, whether the sensitivity could be improved, and how to eventually optimize the grid. These investigations can be conducted numerically, with adequate and adapted volume conduction models.
Commonly, in such models, electrodes are considered to record the potential in just a single point. However, we have shown the importance of explicitly including electrode properties in volume conduction models for accurately interpreting ECoG measurements. To achieve this type of simulation, the Finite Element Method for useful neuroscience simulations (FEMfuns) was developed and tested. FEMfuns allows knowledgeable neuroscientists to solve the forward problem in a variety of different geometrical domains, including various types of source models and electrode properties, such as resistive and capacitive materials, and the double layer that exists at the electrode-tissue interface. As part of the project Into the Brain, we will incorporate FEMfuns into FieldTrip to make these analyses more readily available to the neuroscience community.
As the first step, we have created functions to add electrodes to an existing finite element head model. The head model and electrode positions are created within FieldTrip, after which the forward solution will be found using FEMfuns. Next, the full integration between FieldTrip and FEMfuns will be developed to allow for the integrated use of pre-processing/source analysis routines and detailed forward simulations.
AMBITION: Measuring Stroke Recovery
Mohamed Irfan Mohamed Refai
Requirements for self-directed home-based and personalized arm rehabilitation for stroke patients, using a user centered design approach
Nienja Langerak – Erasmus MC
Introduction: To improve upper limb capacity in stroke patients, a high number of exercise repetitions is recommended. However, during usual therapy sessions the intensity often remains low. Telerehabilitation interventions have the opportunity to achieve high intensities of exercise therapy performed by the patient independently from a therapist. Despite the advantages of telerehabilitation, both patients and therapists experience barriers in using such devices in clinical practice and daily life situations. Therefore, this study describes the requirements for a upper limb telerehabilitation device for stroke patients (ArmCoach4Stroke), form a user perspective.
Methods: This study is based on a user-centered design approach to define the requirements for the ArmCoach4Stroke. We performed a literature review, conducted several interviews and focus groups with end-users: patients, therapists and caregivers. We discussed the results of the literature study, interviews and focus groups within our project meetings iteratively and developed a user journey and user scenario’s. Based on those discussions we performed a requirement analysis, using the MoSCoW method for prioritizing the requirements.
Results: We present a list of functional requirements for the AC4S.
Spatial Summation Investigated using Intraepidermal Electrical Stimulation
Niels Jansen – University of Twente
Spatial summation to nociceptive stimuli is a central mechanism which has been found to be altered in several chronic pain syndromes such as knee osteoarthritis and lateral epicondylalgia, while being unaltered in others such as fibromyalgia or low back pain. In this study, it is explored whether and how spatial summation can be evaluated via intra-epidermal electrical stimulation (IES). To explore this, in 15 healthy subjects thresholds to three stimulus types were simultaneously tracked: single-pulse (SP) stimuli provided through either one of two IES-electrodes placed on the right volar forearm (~2 cm apart), or through both electrodes (DE stimuli) simultaneously. In order to evaluate spatial summation with this protocol, the threshold to one electrode may not be dominant (i.e. significantly lower threshold) over the other electrode. In about all cases, the thresholds to the SP stimuli to the two IES electrodes started equal. In about half of the cases the thresholds to the SP stimuli remained approximately equal, and spatial summation to the DE stimuli could be observed. In the other half of the cases, the threshold to the SP stimuli to one electrode became significantly lower than the other over the course of the experiment. In these cases, spatial summation to the DE stimuli could not be observed as the threshold was equal to the threshold to the SP stimuli of the dominant electrode. Unequal thresholds to the SP stimuli to either one of the two IES electrodes were expected due to differences in the electrocutaneous interface, but then to emerge already from the start – instead of over the course – of the experiment. These findings provide insights into mechanisms resulting in habituation to the stimuli.