Hemm-Ode, Simone
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How sample size impacts probabilistic stimulation maps in deep brain stimulation
Probabilistic stimulation maps of deep brain stimulation (DBS) effect based on voxel-wise statistics (p-maps) have increased in literature over the last decade. These p-maps require correction for Type-1 errors due to multiple testing based on the same data. Some analyses do not reach overall significance, and this study aims to evaluate the impact of sample size on p-map computation. A dataset of 61 essential tremor patients treated with DBS was used for the investigation. Each patient contributed with four stimulation settings, one for each contact. From the dataset, 5 to 61 patients were randomly sampled with replacement for computation of p-maps and extraction of high- and low-improvement volumes. For each sample size, the process was iterated 20 times with new samples generating in total 1140 maps. The overall p-value corrected for multiple comparisons, significance volumes, and dice coefficients (DC) of the volumes within each sample size were evaluated. With less than 30 patients (120 simulations) in the sample, the variation in overall significance was larger and the median significance volumes increased with sample size. Above 120 simulations, the trends stabilize but present some variations in cluster location, with a highest median DC of 0.73 for n = 57. The variation in location was mainly related to the region between the high- and low-improvement clusters. In conclusion, p-maps created with small sample sizes should be evaluated with caution, and above 120 simulations in single-center studies are probably required for stable results.
Experimental assessment of the performances of an anisotropic magnetoresistive sensor after exposure to strong magnetic fields
On-chip magnetometers are already integrated within long-term implants such as cardiac implantable electronic devices. They are also good candidates to be integrated within the next generations of brain stimulation electrodes to provide their position and orientation. In all cases, long-term implants are expected to be at least certified as MRI conditional. We investigated the resilience to the exposure to 3 T and 7 T of an anisotropic magnetoresistive sensor integrating a set/reset function. The sensitivity, non-linearity, and offset of a batch of 63 identical sensors were not affected by the exposure. These preliminary results provide new insights on the usability of magnetoresistive sensors for biomedical applications requiring MRI conditionality.
Naming images in aphasia: effects of illustrative and photographic images on naming performance in people with and without aphasia
Background: Picture naming is a common tool in aphasia diagnosis and therapy. However, opin-ions differ as to which type of image (e.g., photographs, drawings) is most suitable for naming tasks and whether there is a difference on naming correctness and latencies based on image type. Moreover, recent studies have mainly analysed colour photographs and black-and-white line drawings leaving out image types like graphic representations that apply image features that can facilitate naming such as colour, controlled size, or texture. Aims: To shed more light on ap-propriate image types for persons with aphasia, we created graphic representations depicting nouns and verbs and compared them to photographic stimuli in a naming task including persons with aphasia (PWA) and a control group (CG). Methods & Procedures: 33 PWA and 33 age matched persons (CG) participated in the study. Naming correctness and latencies were meas-ured in two different conditions: concepts depicted as coloured photographs vs. as graphic rep-resentations. 128 pictures of linguistically controlled German-language concepts (64 nouns, 64 verbs) had to be named. The designed graphic stimuli were developed by professional designers based on photographs. The photographs were selected from stock image databases according to a defined image concept. This image concept was based on empirical findings regarding im-age features that facilitate naming (e.g., colour, texture, shading) and was applied to the selec-tion of the photographs as well as to the creation of the graphic representations. The images were presented in pseudo-randomized sequences on a tablet and all reactions of the participants were videotaped. The data from the main study was analysed using generalized linear mixed models (GLMM) and linear mixed models (LMM).
Kooperation von Logopädinnen und Logopäden in Forschung und klinischer Praxis im Aphasieprojekt «E-Inclusion»
Im Zuge der evidenzbasierten Praxis sind im Bereich der Logopädie/Sprachtherapie neben der Praxisexper - tise wissenschaftliche Erkenntnisse in die Therapie zu integrieren. Dafür wird mehr fachspezifische Forschung benötigt, die auf Unterstützung der Praxis angewiesen ist. Das Ziel des Artikels ist es, die für Logopädie-For - schung notwendige intradisziplinäre Kooperation von logopädischen Forscherinnen und Forschern sowie Prak- tikerinnen und Praktikern anhand des interdisziplinären Aphasieprojektes «E-Inclusion» der Fachhochschule Nordwestschweiz (FHNW) zu beleuchten. Dazu wird das Aphasieprojekt vorgestellt, welches vier Ziele verfolgte: (1) Auswirkungen von Dialekt und Hochdeutsch sowie (2) von Fotografien und Illustrationen auf die Bildbenenn- leistung bei u. a. Personen mit Aphasie zu untersuchen, (3) mithilfe akustisch-objektiver Sprachsignalanalysen Leistungsveränderungen der Aphasie zu ermitteln und (4) aus diesen Erkenntnissen eine Prototypen-Appli- kation zu entwickeln. Nach der Projektvorstellung gewähren logopädische Praktikerinnen und Praktiker aus Partnerinstitutionen sowie das logopädische Forschungsteam Einblick in die intradisziplinäre Kooperation. Ins- besondere die Rekrutierung der Studienteilnehmenden erforderte eine enge Zusammenarbeit. Als Resultat des Artikels zeigt sich, dass die Kooperation auch unter erschwerten Bedingungen wie zunehmender Zeitdruck im klinisch-therapeutischen Setting für beide Seiten erfolgreich, bedeutsam und bereichernd war. Daraus abgelei- tete Erkenntnisse für kooperative Projekte werden im Fazit dieses Artikels formuliert. Zukünftig können so Logo- pädinnen und Logopäden aus Forschung und Praxis, wie auch Betroffene, von der inter- und intradisziplinären Kooperation im Bereich der Logopädie bzw. in Folgeprojekten des «E-Inclusion»-Forschungsteams profitieren.
Test-re-test reliability and dynamics of the Fukuda–Unterberger stepping test
The Fukuda-stepping-test (FST), i.e., repetitive walking on the spot while blindfolded, has been proposed as a means to assess the integrity of the vestibular pathways. While its sensitivity to detect abnormalities in patients is limited, it may be useful in studying the physiology of the subjective-straight-ahead (SSA). Considering reported systematic shifts in SSA in humans, we hypothesize that such asymmetries arise from individual differences in the orientation/configuration of the macular organs and in central processing of vestibular input. We hypothesize that such asymmetries are stable over time in individual subjects. Alternatively, such asymmetries may arise from random noise in the sensory/motor systems involved, demonstrating low reproducibility over time. Materials and methods: Twenty-four subjects walked on the spot over 60 s while blindfolded. Using an inertial measurement unit (IMU) placed at the chest, angular deviations were recorded and compared to manually-measured final positions. Both static (direction, magnitude) and dynamic (time-to-onset of deviation, pattern of deviations) parameters were retrieved from the yaw slopes. Significant deviations were found in 15/24 participants for the manual measurements (leftwards = 8; rightwards = 7), whereas when using the IMU-sensor 13/24 participants showed significant shifts (leftwards = 9; rightwards = 4). There was a high correlation (0.98) between manually measured rotation angles (average absolute deviations = 58.0 deg ± 48.6 deg; intra-individual variability = 39 deg ± 24 deg) and sensor-based yaw slopes (1.00 deg/s ± 0.88 deg/s; 0.67 deg/s ± 0.41 deg/s). Relevant yaw deviation was detected 22.1 s ± 12.3 s (range = 5.6 s-59.2 s) after the onset of marching (no relevant yaw-deviation in 15/139 measurements), showing a mostly linear behavior over time. Conclusion: We observed significant inter-individual variability in task performance in the FST, reproducing findings from previous studies. With test-re-test reliability being moderate only, but at the same time observing a preference in the side of shifts in most trials and subjects, we conclude that likely both individually varying estimates of straight-ahead and random noise contribute to the pattern of angular deviations observed. Using an IMU-sensory based approach, additional dynamic parameters could be retrieved, emphasizing the value of such a quantitative approach over manual measurements. Such an approach may provide useful additional information to distinguish patients from healthy controls.
Towards a new generation of electromagnetic navigation system for deep brain stimulation
Heading direction is significantly biased by preceding whole-body roll-orientation while lying
Background: After a prolonged static whole-body roll-tilt, a significant bias of the internal estimates of the direction of gravity has been observed when assessing the subjective visual vertical. Objective: We hypothesized that this post-tilt bias represents a more general phenomenon, broadly affecting spatial orientation and navigation. Specifically, we predicted that after the prolonged roll-tilt to either side perceived straight-ahead would also be biased. Methods: Twenty-five healthy participants were asked to rest in three different lying positions (supine, right-ear-down, and left-ear-down) for 5 min (“adaptation period”) prior to walking straight-ahead blindfolded for 2 min. Walking was recorded with the inertial measurement unit sensors attached to different body locations and with sensor shoe insoles. The raw data was segmented with a gait–event detection method. The Heading direction was determined and linear mixed-effects models were used for statistical analyses. Results: A significant bias in heading into the direction of the previous roll-tilt position was observed in the post-adaptation trials. This bias was identified in both measurement systems and decreased again over the 2-min walking period. Conclusions: The bias observed further confirms the influence of prior knowledge on spatial orientation and navigation. Specifically, it underlines the broad impact of a shifting internal estimate of direction of gravity over a range of distinct paradigms, illustrating similar decay time constants. In the broader context, the observed bias in perceived straight-ahead emphasizes that getting up in the morning after a good night's sleep is a vulnerable period, with an increased risk of falls and fall-related injuries due to non-availability of optimally tuned internal estimates of the direction of gravity and the direction of straight-ahead.
An online movement and tremor identification algorithm for evaluation during deep brain stimulation
INTRODUCTION: Deep brain stimulation (DBS) is widely used to alleviate symptoms of movement disorders. During intraoperative stimulation the influence of active or passive movements on the neuronal activity is often evaluated but the evaluation remains mostly subjective. The objective of this paper is to investigate the potential of a previously developed Weighted-frequency Fourier Linear combiner and Kalman filter-based recursive algorithm to identify tremor phases and types. METHODS: Ten accelerometer recordings from eight patients were acquired during DBS from which 186 phases were manually annotated into: rest, postural and kinetic phase without tremor, and rest, postural and kinetic phase with tremor. The method first estimates the instantaneous tremor frequency and then decomposes the motion signal into voluntary and tremorous parts. The tremorous part is used to quantify tremor and the voluntary part to differentiate rest, postural and kinetic phases. RESULTS: Instantaneous tremor frequency and amplitude are successfully tracked online. The overall accuracy for tremorous phases only is 89.1% and 76.3% when also non-tremorous phases are considered. Two main misclassification cases are identified and further discussed. CONCLUSION: The results demonstrate the potential of the developed algorithm as an online tremorous movement classifier. It would benefit from a more advanced tremor detector but nevertheless the obtained digital biomarkers offer an evidence-based analysis and could optimize the efficacy of DBS treatment.
Deep brain stimulation: emerging tools for simulation, data analysis, and visualization
Deep brain stimulation (DBS) is a well-established neurosurgical procedure for movement disorders that is also being explored for treatment-resistant psychiatric conditions. This review highlights important consideration for DBS simulation and data analysis. The literature on DBS has expanded considerably in recent years, and this article aims to identify important trends in the field. During DBS planning, surgery, and follow up sessions, several large data sets are created for each patient, and it becomes clear that any group analysis of such data is a big data analysis problem and has to be handled with care. The aim of this review is to provide an update and overview from a neuroengineering perspective of the current DBS techniques, technical aids, and emerging tools with the focus on patient-specific electric field (EF) simulations, group analysis, and visualization in the DBS domain. Examples are given from the state-of-the-art literature including our own research. This work reviews different analysis methods for EF simulations, tractography, deep brain anatomical templates, and group analysis. Our analysis highlights that group analysis in DBS is a complex multi-level problem and selected parameters will highly influence the result. DBS analysis can only provide clinically relevant information if the EF simulations, tractography results, and derived brain atlases are based on as much patient-specific data as possible. A trend in DBS research is creation of more advanced and intuitive visualization of the complex analysis results suitable for the clinical environment.