Surjo Soekadar | University of Tübingen (original) (raw)

Papers by Surjo Soekadar

Direct brain control of advanced robotic systems promises substantial improvements in health care... more Direct brain control of advanced robotic systems promises substantial improvements in health care, for example, to restore intuitive control of hand movements required for activities of daily living in quadriplegics, like holding a cup and drinking, eating with cutlery, or manipulating different objects. However, such integrated, brain- or neural-controlled robotic systems have yet to enter broader clinical use or daily life environments. We demonstrate full restoration of independent daily living activities, such as eating and drinking, in an everyday life scenario across six paraplegic individuals (five males, 30 ± 14 years) who used a noninvasive, hybrid brain/neural hand exoskeleton (B/NHE) to open and close their paralyzed hand. The results broadly suggest that brain/neural-assistive technology can restore autonomy and independence in quadriplegic individuals’ everyday life

Stroke, 2017

The laterality of the lesioned hemisphere is often overlooked in stroke recovery research due to ... more The laterality of the lesioned hemisphere is often overlooked in stroke recovery research due to small sample sizes. Here, we used a well-powered dataset from ENIGMA Stroke Recovery (a consortium that harmonizes post-stroke MRIs and behavioral data worldwide; http://enigma.usc.edu) to analyze the effects of left (LHL) versus right (RHL) hemisphere lesions on motor performance. Given the different functional roles of each hemisphere, we hypothesized that the LHL group should show better motor performance, and, consequently, different brain-behavior relationships, compared to the RHL group. Data from over 2000 stroke patients across 20 sites worldwide has been committed. To date, structural T1-weighted MRIs from n=343 (10 sites) have been analyzed (LHL n=174; RHL n=169). ENIGMA protocols extracted volumes of subcortical regions of interest and provided quality control. Regression analyses examined brain volumes as predictors of motor outcomes. Motor scores were combined across scales/...

Data in Brief, 2021

Transcranial alternating current stimulation (tACS) can affect perception, learning and cognition... more Transcranial alternating current stimulation (tACS) can affect perception, learning and cognition, but the underlying mechanisms are not well understood. A promising strategy to elucidate these mechanisms aims at applying tACS while electric or magnetic brain oscillations targeted by stimulation are recorded. However, reconstructing brain oscillations targeted by tACS remains a challenging problem due to stimulation artifacts. Besides lack of an established strategy to effectively supress such stimulation artifacts, there are also no resources available that allow for the development and testing of new and effective tACS artefact suppression algorithms, such as adaptive spatial filtering using beamforming or signal-space projection. Here, we provide a full dataset comprising encephalographic (EEG) recordings across six healthy human volunteers who underwent 10-Hz amplitude-modulated tACS (AM-tACS) during a 10-Hz steady-state visually evoked potential (SSVEP) paradigm. Moreover, data...

Brain Communications, 2021

Up to two-thirds of stroke survivors experience persistent sensorimotor impairments. Recovery rel... more Up to two-thirds of stroke survivors experience persistent sensorimotor impairments. Recovery relies on the integrity of spared brain areas to compensate for damaged tissue. Deep grey matter structures play a critical role in the control and regulation of sensorimotor circuits. The goal of this work is to identify associations between volumes of spared subcortical nuclei and sensorimotor behaviour at different timepoints after stroke. We pooled high-resolution T1-weighted MRI brain scans and behavioural data in 828 individuals with unilateral stroke from 28 cohorts worldwide. Cross-sectional analyses using linear mixed-effects models related post-stroke sensorimotor behaviour to non-lesioned subcortical volumes (Bonferroni-corrected, P < 0.004). We tested subacute (≤90 days) and chronic (≥180 days) stroke subgroups separately, with exploratory analyses in early stroke (≤21 days) and across all time. Sub-analyses in chronic stroke were also performed based on class of sensorimotor...

SpringerBriefs in Electrical and Computer Engineering, 2019

Controlling advanced robotic systems with brain signals promises substantial improvements in heal... more Controlling advanced robotic systems with brain signals promises substantial improvements in health care, for example, to restore intuitive control of hand movements after severe stroke or spinal cord injuries (SCI). However, such integrated, brain- or neural-controlled robotic systems have yet to enter broader clinical use or daily life environments. The main challenge to integrate such systems in everyday life environments relates to the reliability of brain-control, particularly when brain signals are recorded non-invasively. Using a non-invasive, hybrid EEG-EOG-based brain/neural hand exoskeleton (B/NHE), we demonstrate full restoration of activities of daily living (ADL), such as eating and drinking, across six paraplegic individuals (five males, 30 ± 14 years) outside the laboratory. In a second set of experiments, we show that even whole-arm exoskeleton control is feasible and safe by combining hybrid brain/neural control with vision-guided and context-sensitive autonomous robotics. Given that recent studies indicate neurological recovery after chronic stroke or SCI when brain-controlled assistive technology is repeatedly used for 1–12 months, we suggest that combining an assistive and rehabilitative approach may further promote brain-machine interface (BMI) technology as a standard therapy option after stroke and SCI. In such scenario, brain/neural-assistive technology would not only have an immediate impact on the quality of life and autonomy of individuals with brain or spinal cord lesions but would also foster neurological recovery by stimulating functional and structural neuroplasticity.

Brain oscillations, e.g. measured by electro- or magnetoencephalography (EEG/MEG), are causally l... more Brain oscillations, e.g. measured by electro- or magnetoencephalography (EEG/MEG), are causally linked to brain functions that are fundamental for perception, cognition and learning. Recent advances in neurotechnology provide means to non-invasively target these oscillations using frequency-tuned amplitude-modulated transcranial alternating current stimulation (AM-tACS). However, online adaptation of stimulation parameters to ongoing brain oscillations remains an unsolved problem due to stimulation artifacts that impede such adaptation, particularly at the target frequency. Here, we introduce a real-time compatible artifact rejection algorithm (Stimulation Artifact Source Separation, SASS) that overcomes this limitation. SASS is a spatial filter (linear projection) removing EEG signal components that are maximally different in the presence versus absence of stimulation. This enables the reliable removal of stimulation-specific signal components, while leaving physiological signal co...

Human Brain Mapping, 2020

The goal of the Enhancing Neuroimaging Genetics through Meta-Analysis (ENIGMA) Stroke Recovery wo... more The goal of the Enhancing Neuroimaging Genetics through Meta-Analysis (ENIGMA) Stroke Recovery working group is to understand brain and behavior relationships using well-powered meta-and mega-analytic approaches. ENIGMA Stroke Recovery has data from over 2,100 stroke patients collected across 39 research studies and K01HD091283,

Sensors, 2019

When combined with assistive robotic devices, such as wearable robotics, brain/neural-computer in... more When combined with assistive robotic devices, such as wearable robotics, brain/neural-computer interfaces (BNCI) have the potential to restore the capabilities of handicapped people to carry out activities of daily living. To improve applicability of such systems, workload and stress should be reduced to a minimal level. Here, we investigated the user’s physiological reactions during the exhaustive use of the interfaces of a hybrid control interface. Eleven BNCI-naive healthy volunteers participated in the experiments. All participants sat in a comfortable chair in front of a desk and wore a whole-arm exoskeleton as well as wearable devices for monitoring physiological, electroencephalographic (EEG) and electrooculographic (EoG) signals. The experimental protocol consisted of three phases: (i) Set-up, calibration and BNCI training; (ii) Familiarization phase; and (iii) Experimental phase during which each subject had to perform EEG and EoG tasks. After completing each task, the NASA...

Scientific Reports, 2019

Self-initiated voluntary acts, such as pressing a button, are preceded by a surface-negative elec... more Self-initiated voluntary acts, such as pressing a button, are preceded by a surface-negative electrical brain potential, the Bereitschaftspotential (BP), that can be recorded over the human scalp using electroencephalography (EEG). While the BP's early component (BP1, generated in the supplementary and cingulate motor area) was linked to motivational, intentional and timing properties, the BP's late component (BP2, generated in the primary motor cortex) was found to be linked to motor execution and performance. Up to now, the BP required to initiate voluntary acts has only been recorded under well-controlled laboratory conditions, and it was unknown whether possible life-threatening decision making, e.g. required to jump into a 192-meter abyss, would impact this form of brain activity. Here we document for the first time pre-movement brain activity preceding 192-meter bungee jumping. We found that the BP's spatiotemporal dynamics reflected by BP1 and BP2 are comparable before 192-meter bungee jumping and jumping from 1-meter. These results, possible through recent advancements in wireless and portable EEG technology, suggest that possible life-threatening decisionmaking has no impact on the BP's spatiotemporal dynamics.

This checklist is intended to encourage robust experimental design and clear reporting for clinic... more This checklist is intended to encourage robust experimental design and clear reporting for clinical and cognitive-behavioural neurofeedback experiments.

Neuromodulation: Technology at the Neural Interface, 2018

Objectives: Dorsal root ganglion stimulation (DRGS) has been used successfully against localized ... more Objectives: Dorsal root ganglion stimulation (DRGS) has been used successfully against localized neuropathic pain. Nevertheless, the effects of DRGS on pain processing, particularly at the cortical level, remain largely unknown. In this study, we investigated whether positive responses to DRGS treatment would alter patients' laser-evoked potentials (LEP). Methods: We prospectively enrolled 12 adult patients with unilateral localized neuropathic pain in the lower limbs or inguinal region and followed them up for six months. LEPs were assessed at baseline, after one month of DRGS, and after six months of DRGS. Clinical assessment included the Numerical Rating Scale (NRS), Brief Pain Inventory (BPI), SF-36, and Beck Depression Inventory (BDI). For each patient, LEP amplitudes and latencies of the N2 and P2 components on the deafferented side were measured and compared to those of the healthy side and correlated with pain intensity, as measured with the NRS. Results: At the one-and six-month follow-ups, N2-P2 amplitudes were significantly greater and NRS scores were significantly lower compared with baseline (all p's < 0.01). There was a negative correlation between LEP amplitudes and NRS scores (r s = −0.31, p < 0.10). Conclusions: DRGS is able to restore LEPs to normal values in patients with localized neuropathic pain, and LEP alterations are correlated with clinical response in terms of pain intensity.

eLife, 2018

To date there exists no reliable method to non-invasively upregulate or downregulate the state of... more To date there exists no reliable method to non-invasively upregulate or downregulate the state of the resting human motor system over a large dynamic range. Here we show that an operant conditioning paradigm which provides neurofeedback of the size of motor evoked potentials (MEPs) in response to transcranial magnetic stimulation (TMS), enables participants to self-modulate their own brain state. Following training, participants were able to robustly increase (by 83.8%) and decrease (by 30.6%) their MEP amplitudes. This volitional up-versus down-regulation of corticomotor excitability caused an increase of late-cortical disinhibition (LCD), a TMS derived read-out of presynaptic GABAB disinhibition, which was accompanied by an increase of gamma and a decrease of alpha oscillations in the trained hemisphere. This approach paves the way for future investigations into how altered brain state influences motor neurophysiology and recovery of function in a neurorehabilitation context.

Scientific Reports, 2018

Arm and finger paralysis, e.g. due to brain stem stroke, often results in the inability to perfor... more Arm and finger paralysis, e.g. due to brain stem stroke, often results in the inability to perform activities of daily living (ADLs) such as eating and drinking. Recently, it was shown that a hybrid electroencephalography/electrooculography (EEG/EOG) brain/neural hand exoskeleton can restore hand function to quadriplegics, but it was unknown whether such control paradigm can be also used for fluent, reliable and safe operation of a semi-autonomous whole-arm exoskeleton restoring ADLs. To test this, seven abled-bodied participants (seven right-handed males, mean age 30 ± 8 years) were instructed to use an EEG/EOG-controlled whole-arm exoskeleton attached to their right arm to perform a drinking task comprising multiple sub-tasks (reaching, grasping, drinking, moving back and releasing a cup). Fluent and reliable control was defined as average 'time to initialize' (TTI) execution of each sub-task below 3 s with successful initializations of at least 75% of sub-tasks within 5 s. During use of the system, no undesired side effects were reported. All participants were able to fluently and reliably control the vision-guided autonomous whole-arm exoskeleton (average TTI 2.12 ± 0.78 s across modalities with 75% successful initializations reached at 1.9 s for EOG and 4.1 s for EEG control) paving the way for restoring ADLs in severe arm and hand paralysis. Arm and hand paralysis due to lesions of the central or peripheral nervous system is the most common reason for long-term disability in the adulthood 1. Particularly high-cervical spinal cord injuries, stroke or plexus brachialis avulsions resulting in a complete loss of arm and finger function have a substantial impact on the ability to perform various activities of daily living (ADLs), e.g. eating and drinking independently 2,3. Over the last years, various upper-limb robotic systems were developed to mobilize the upper limb and fingers, e.g. in the context of rehabilitation therapies 4-7. Other promising robotic approaches to restore ADLs include gaze-based teleprosthetics 8. While these systems were often immobile and designed to be used in rehabilitation facilities, recent advances in systems integration yielded the development of portable robotic arms with grippers 9,10 or lightweight whole-arm 11 or hand exoskeletons 12,13 that can be used in everyday life environments to assist in ADLs. While assistive robotic arms were mainly designed for individuals with complete tetraplegia and

Annals of clinical and translational neurology, 2018

Brain-computer interfaces (BCIs) can provide sensory feedback of ongoing brain oscillations, enab... more Brain-computer interfaces (BCIs) can provide sensory feedback of ongoing brain oscillations, enabling stroke survivors to modulate their sensorimotor rhythms purposefully. A number of recent clinical studies indicate that repeated use of such BCIs might trigger neurological recovery and hence improvement in motor function. Here, we provide a first meta-analysis evaluating the clinical effectiveness of BCI-based post-stroke motor rehabilitation. Trials were identified using MEDLINE, CENTRAL, PEDro and by inspection of references in several review articles. We selected randomized controlled trials that used BCIs for post-stroke motor rehabilitation and provided motor impairment scores before and after the intervention. A random-effects inverse variance method was used to calculate the summary effect size. We initially identified 524 articles and, after removing duplicates, we screened titles and abstracts of 473 articles. We found 26 articles corresponding to BCI clinical trials, of t...

Psychopharmacology, 2018

Sleep-dependent memory consolidation depends on the concerted reactivation of memories in the hip... more Sleep-dependent memory consolidation depends on the concerted reactivation of memories in the hippocampo-neocortical system. The communication of reactivated information from the hippocampus to the neocortex is assumed to be enabled by low levels of acetylcholine, particularly during slow-wave sleep (SWS). Recent studies suggest that the reactivation of memories does not only occur spontaneously but can also be externally triggered by re-presenting learning-associated cues during sleep. Here we investigated whether the beneficial effect of cued memory reactivation during sleep depends on similar mechanisms as spontaneous reactivation, and specifically on low cholinergic tone. In two experimental nights, healthy volunteers learned a visuo-spatial memory task in the presence of an odor before going to sleep for 40 min. In one night, subjects were presented with the odor again during SWS, whereas in the other night they received an odorless vehicle. In half of the subjects, the availab...

Science (New York, N.Y.), Jun 30, 2017

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Science Robotics, 2016

A noninvasive, hybrid brain/neural hand exoskeleton restored intuitive control of grasping motion... more A noninvasive, hybrid brain/neural hand exoskeleton restored intuitive control of grasping motion, restoring independent activities to quadriplegics.

Frontiers in cellular neuroscience, 2016

Frontal midline theta (FMT) oscillations (4-8 Hz) are strongly related to cognitive and executive... more Frontal midline theta (FMT) oscillations (4-8 Hz) are strongly related to cognitive and executive control during mental tasks such as memory processing, arithmetic problem solving or sustained attention. While maintenance of temporal order information during a working memory (WM) task was recently linked to FMT phase, a positive correlation between FMT power, WM demand and WM performance was shown. However, the relationship between these measures is not well understood, and it is unknown whether purposeful FMT phase manipulation during a WM task impacts FMT power and WM performance. Here we present evidence that FMT phase manipulation mediated by transcranial alternating current stimulation (tACS) can block WM demand-related FMT power increase (FMTΔpower) and disrupt normal WM performance. Twenty healthy volunteers were assigned to one of two groups (group A, group B) and performed a 2-back task across a baseline block (block 1) and an intervention block (block 2) while 275-sensor m...

Handbook of Neuroethics, 2014