Revisiting Transcranial Light Stimulation as a Stroke Therapeutic-Hurdles and Opportunities

Near-infrared laser therapy, a special form of transcranial light therapy, has been tested as an acute stroke therapy in three large clinical trials. While the NEST trials failed to show the efficacy of light therapy in human stroke patients, there are many lingering questions and lessons that can be learned. In this review, we summarize the putative mechanism of light stimulation in the setting of stroke, highlight barriers, and challenges during the translational process, and evaluate light stimulation parameters, dosages and safety issues, choice of outcomes, effect size, and patient selection criteria. In the end, we propose potential future opportunities with transcranial light stimulation as a cerebroprotective or restorative tool for future stroke treatment.

Numerical and experimental evaluation of low-intensity transcranial focused ultrasound wave propagation using human skulls for brain neuromodulation

BACKGROUND

Low-intensity transcranial focused ultrasound (tFUS) has gained considerable attention as a promising noninvasive neuromodulatory technique for human brains. However, the complex morphology of the skull hinders scholars from precisely predicting the acoustic energy transmitted and the region of the brain impacted during the sonication. This is due to the fact that different ultrasound frequencies and skull morphology variations greatly affect wave propagation through the skull.

PURPOSE

Although the acoustic properties of human skull have been studied for tFUS applications, such as tumor ablation using a multielement phased array, there is no consensus about how to choose a single-element focused ultrasound (FUS) transducer with a suitable frequency for neuromodulation. There are interests in exploring the magnitude and dimension of tFUS beam through human parietal bone for modulating specific brain lobes. Herein, we aim to investigate the wave propagation of tFUS on human skulls to understand and address the concerns above.

METHODS

Both experimental measurements and numerical modeling were conducted to investigate the transmission efficiency and beam pattern of tFUS on five human skulls (C3 and C4 regions) using single-element FUS transducers with six different frequencies (150-1500 kHz). The degassed skull was placed in a water tank, and a calibrated hydrophone was utilized to measure acoustic pressure past it. The cranial computed tomography scan data of each skull were obtained to derive a high-resolution acoustic model (grid point spacing: 0.25 mm) in simulations. Meanwhile, we modified the power-law exponent of acoustic attenuation coefficient to validate numerical modeling and enabled it to be served as a prediction tool, based on the experimental measurements.

RESULTS

The transmission efficiency and -6 dB beamwidth were evaluated and compared for various frequencies. An exponential decrease in transmission efficiency and a logarithmic decrease of -6 dB beamwidth with an increase in ultrasound frequency were observed. It is found that a >750 kHz ultrasound leads to a relatively lower tFUS transmission efficiency (<5%), whereas a <350 kHz ultrasound contributes to a relatively broader beamwidth (>5 mm). Based on these observations, we further analyzed the dependence of tFUS wave propagation on FUS transducer aperture size.

CONCLUSIONS

We successfully studied tFUS wave propagation through human skulls at different frequencies experimentally and numerically. The findings have important implications to predict tFUS wave propagation for ultrasound neuromodulation in clinical applications, and guide researchers to develop advanced ultrasound transducers as neural interfaces.

In vivo Measurements of Electric Fields During Cranial Electrical Stimulation in the Human Brain

Cranial electrical stimulation (CES) has been applied at various current levels in both adults and children with neurological conditions with seemingly promising but somewhat inconsistent results. Stimulation-induced spatial electric fields (EFs) within a specific brain region are likely a significant contributing factor for the biological effects. Although several simulation models have been used to predict EF distributions in the brain, these models actually have not been validated by in vivo CES-induced EF measurements in the live human brain. This study directly measured the CES-induced voltage changes with implanted stereotactic-electroencephalographic (sEEG) electrodes in twenty-one epilepsy participants (16 adults and 5 children) and then compared these measured values with the simulated ones obtained from the personalized models. In addition, we further investigated the influence of stimulation frequency, intensity, electrode montage and age on EFs in parts of participants. We found both measured voltages and EFs obtained in vivo are highly correlated with the predicted ones in our cohort (Voltages: r = 0.93, p &lt; 0.001; EFs: r = 0.73, p &lt; 0.001). In white matter and gray matter, the measured voltages linearly increased when the stimulation intensity increased from 5 to 500 μA but showed no significant changes (averaged coefficient of variation &lt;4.10%) with changing stimulation frequency from 0.5 to 200 Hz. Electrode montage, but not age, significantly affects the distribution of the EFs (n = 5, p &lt; 0.01). Our in vivo measurements demonstrate that the individualized simulation model can reliably predict the CES-induced EFs in both adults and children. It also confirms that the CES-induced EFs highly depend on the electrode montages and individual anatomical features.

Abstract WMP37: Differential Montage Effect On Cortical Excitability In Ischemic Stroke Patients By Single Session Of High Amperage Transcranial Direct Current Stimulation

Background and Objective: We aim to assess the cortical excitability under three montages with single session of transcranial direct current stimulation (tDCS) at 4 mA on ischemic stroke patients.

Methods: Adult subjects with first-ever unilateral ischemic stroke ≥6 months and inducible motor evoked potentials (MEP) underwent 3 sessions (washed out ≥2 days apart) of 30 minutes 4 mA tDCS in anodal, cathodal or bihemispheric montage (in pseudorandom order) combined with t upper extremity repetitive task training administered by an Occupational Therapist. We collected MEP responses to transcranial magnetic stimulation (TMS) single pulse, short intracortical inhibition (SICI, 3 ms) and intracortical facilitation (ICF, 15 ms) on bilateral abductor pollicis brevis (APB) muscles at baseline and four post-stimulation timepoints 12 minutes apart. We also monitored safety by recording adverse events, surveying subjects with a questionnaire on tolerability issues and collecting biometric measures (body resistance, skin temperature under the tDCS electrode).

Results: Eighteen subjects completed 54 tDCS sessions in total. We observed montage ( P <0.0001) and time ( P <0.01) effects only on the lesioned hemisphere, with bihemispheric tDCS showing relatively higher peak-to-peak MEP. Lack of montage effect in baseline ( P >0.949) suggested sufficient washout interval across the visits. No subjects experienced any adverse events. Biometric measures and tolerability were comparable across the three montages. The most common tolerability issue was transient redness under the tDCS electrodes (70% at anode, 48% at cathode).

Conclusions: The bihemispheric montage increased ipsilateral cortical excitability the most in a single session of 4 mA tDCS in chronic ischemic stroke patients. Additionally, a current level of 4 mA is safe and tolerable over multiple sessions.

Structural and Functional Imaging of the Retina in Central Retinal Artery Occlusion - Current Approaches and Future Directions

Central retinal artery occlusion (CRAO) is a form of acute ischemic stroke which affects the retina. Intravenous thrombolysis is emerging as a compelling therapeutic approach. However, it is not known which patients may benefit from this therapy because there are no imaging modalities that adequately distinguish viable retina from irreversibly infarcted retina. The inner retina receives arterial supply from the central retinal artery and there is robust collateralization between this circulation and the outer retinal circulation, provided by the posterior ciliary circulation. Fundus photography can show canonical changes associated with CRAO including a cherry-red spot, arteriolar boxcarring and retinal pallor. Fluorescein angiography provides 2-dimensional imaging of the retinal circulation and can distinguish a complete from a partial CRAO as well as central versus peripheral retinal non-perfusion. Transorbital ultrasonography may assay flow through the central retinal artery and is useful in the exclusion of other orbital pathology that can mimic CRAO. Optical coherence tomography provides structural information on the different layers of the retina and exploratory work has described its utility in determining the time since onset of ischemia. Two experimental techniques are discussed. 1) Retinal functional imaging permits generation of capillary perfusion maps and can assay retinal oxygenation and blood flow velocity. 2) Photoacoustic imaging combines the principles of optical excitation and ultrasonic detection and - in animal studies - has been used to determine the retinal oxygen metabolic rate. Future techniques to determine retinal viability in clinical practice will require rapid, easily used, and reproducible methods that can be deployed in the emergency setting.

Effect of Low Intensity Transcranial Ultrasound Stimulation on Neuromodulation in Animals and Humans: An Updated Systematic Review

Background: Although low-intensity transcranial ultrasound stimulation (LI-TUS) has received more recognition for its neuromodulation potential, there remains a crucial knowledge gap regarding the neuromodulatory effects of LI-TUS and its potential for translation as a therapeutic tool in humans.

Objective: In this review, we summarized the findings reported by recently published studies regarding the effect of LI-TUS on neuromodulation in both animals and humans. We also aim to identify challenges and opportunities for the translation process.

Methods: A literature search of PubMed, Medline, EMBASE, and Web of Science was performed from January 2019 to June 2020 with the following keywords and Boolean operators: [transcranial ultrasound OR transcranial focused ultrasound OR ultrasound stimulation] AND [neuromodulation]. The methodological quality of the animal studies was assessed by the SYRCLE's risk of bias tool, and the quality of human studies was evaluated by the PEDro score and the NIH quality assessment tool.

Results: After applying the inclusion and exclusion criteria, a total of 26 manuscripts (24 animal studies and two human studies) out of 508 reports were included in this systematic review. Although both inhibitory (10 studies) and excitatory (16 studies) effects of LI-TUS were observed in animal studies, only inhibitory effects have been reported in primates (five studies) and human subjects (two studies). The ultrasonic parameters used in animal and human studies are different. The SYRCLE quality score ranged from 25 to 43%, with a majority of the low scores related to performance and detection bias. The two human studies received high PEDro scores (9/10).

Conclusion: LI-TUS appears to be capable of targeting both superficial and deep cerebral structures to modulate cognitive or motor behavior in both animals and humans. Further human studies are needed to more precisely define the effective modulation parameters and thereby translate this brain modulatory tool into the clinic.

Abstract P592: Admission Hyperglycemia is Associated With Subsequent Ischemic Stroke After Transient Ischemic Attack or Minor Stroke: A Secondary Analysis of the POINT Trial

Introduction: Hyperglycemia is associated with increased lesion volume and worse functional outcome after acute ischemic stroke, however, it is not known whether it is associated with further cerebrovascular events. The aim of this study was to examine the association between admission hyperglycemia and subsequent ischemic stroke.

Methods: This was an exploratory analysis of the Platelet Oriented Inhibition in New TIA and Minor Ischemic Stroke (POINT) trial, which compared combined clopidogrel/aspirin with aspirin alone with respect to the primary outcome of subsequent ischemic stroke, myocardial infarction, or vascular death. We dichotomized patients based on a serum glucose threshold of 180mg/dl (chosen a priori based on the upper boundary of the active control arm of SHINE). We calculated hazard ratios (HR) for subsequent ischemic stroke at 90 days via a Cox proportional hazards model adjusting for age, sex, study treatment assignment and vascular risk factors. We performed sensitivity analyses excluding patients with a known history of diabetes and in patients whose index event was a TIA vs. minor stroke.

Results: Of 4,878 patients in this analysis (mean age 64.6 years), 594 (12.2%) were hyperglycemic on presentation and 267 (5.5%) had a subsequent ischemic stroke within 90 days. Admission hyperglycemia was associated with subsequent ischemic stroke (HR 1.88; 95% CI:1.39-2.53, p<0.01). This association persisted after adjustment for relevant covariates (aHR 1.86, 95% CI: 1.37-2.52, p<0.01), in non-diabetic patients (n=3,529, aHR 3.1, 95% CI:1.7-5.7, p<0.01), in patients with TIA (n=2,327, aHR 2.2, 95% CI: 1.2-4.1, p<0.01), and in patients with minor ischemic stroke (n=2,304, aHR = 1.5, 95% CI: 1.1-2.2, p=0.02).

Conclusions: Hyperglycemia portends a higher risk of subsequent ischemic stroke after adjusting for known predictors of stroke recurrence. This study may provide further support to pursuing aggressive secondary prevention strategies in this population.

Abstract MP46: Internal Carotid Artery Web and Acute Ischemic Stroke - A Systematic Review and Meta-Analysis

Introduction: The carotid web is a compelling potential mechanism of embolic ischemic stroke. In this study, we perform a systematic review and meta-analysis to determine the prevalence of ipsilesional carotid webs in patients with acute ischemic stroke.

Methods: We performed a systematic review of prospective and retrospective observational studies enrolling consecutive patients with acute ischemic stroke. We included only studies in which high quality imaging of the cervical vessels was performed and in which the presence or absence of carotid web was adjudicated based on established criteria. The prevalence of carotid web was calculated in each study and pooled prevalence calculated via a random effects model. We also calculated relative risks of carotid web ipsilateral versus contralateral to stroke in the same pool of patients and performed sensitivity analyses including patients with cryptogenic stroke, patients less than 60 and patients with cryptogenic stroke <60.

Results: A systematic review yielded 3,814 patients from 11 studies of whom 1,127 had cryptogenic stroke. We identified 4 studies in which we could derive data on patients <60 with cryptogenic stroke, a total of 332 patients. The relative risk of carotid web ipsilateral versus contralateral to ischemic stroke was 2.6 (95%: 1.6-4.3, p<0.01) in all patients with acute ischemic stroke and 3.0 (95% CI: 1.6-5.8, p<0.01) in patient less than 60 with cryptogenic stroke ( Figure A-C ). The pooled prevalence of ipsilateral carotid web in patients <60 with cryptogenic stroke was 13% (95% CI: 7%-22%; I 2 = 66.1%) ( Figure D ).

Discussion: Carotid webs are more common in young patients with ESUS than in other stroke subtypes. Future studies concerning the diagnosis and secondary prevention of stroke associated with carotid web should focus on this population.

Abstract TMP39: Further Evidence of Safety and Tolerablity on 4 mA Transcranial Direct Current Stimulation (tDCS) in Patients With Ischemic Stroke

Introduction: By the proof of concept, a phase I tDCS current escalation safety study established the safety and tolerability of up to 4 mA with single session application in ischemic stroke patients; however, the sample size is relatively small with only 3 subjects received 4 mA dose in the 3+3 design. We aim to further investigate the safety and tolerability of tDCS at 4 mA currents with multiple sessions.

Hypothesis: tDCS in 4 mA strength is safe and tolerable in three montage conditions (anodal, cathodal and bihemispheric)

Methods: Eighteen aging stroke patients underwent 3 sessions of 4 mA tDCS that are at least 2 days apart: anodal (Anode: lesional C3/C4, Cathode: non-lesional FP1/FP2), cathodal (Anode: lesional FP1/FP2, Cathode: non-lesional C3/C4), or bihemispheric (Anode: lesional C3/C4, Cathode: non-lesional C3/C4). We monitored safety by looking for any adverse event (AE) or serious adverse event (SAE). We measured tolerability using questionnaire/examination. We implemented biometric monitoring (body resistance, skin temperature at tDCS application sites) to ensure the patient safety.

Results: All 18 patients completed all 54 sessions of tDCS (3 sessions per subject) without any adverse event or serious adverse event. Per Questionnaire, the most common tolerability issue was transient redness at tDCS application sites (70% at anode, 48% at cathode, see A). Body resistance was comparable across montages and skin temperature was below body temperature in all tDCS sessions (see B).

Conclusion: Our findings provide further evidence that tDCS at 4 mA is safe and tolerable. The efficacy of 4 mA tDCS is being investigated by NIH StrokeNet-funded study called TRANSPORT2.

Abstract TMP43: Differential Cortical Effect Modulated by Anodal, Cathodal and Bihemispheric Transcranial Direct Current Stimulation (tDCS) in Patients With Ischemic Stroke

Introduction: The differential brain modulatory effects across hemispheres from different montages in stroke patients is not well established. We aimed to investigate the cortical excitability on lesional and contra-lesional hemisphere modulated by anodal, cathodal and bihemispheric montage at 4 mA tDCS strengths.

Hypothesis: Bihemispheric tDCS montage induces more cortical excitability on the lesional hemisphere.

Methods: Eighteen aging stroke patients with unilateral ischemic stroke of 6 or more months and inducible motor evoked potentials (MEP) underwent 3 sessions of 30 minutes 4 mA tDCS combined with occupational therapy. Each session was at least 2 days apart and consisted of one of the 3 different montages: anodal (Anode: lesional C3/C4, Cathode: non-lesional FP1/FP2), cathodal (Anode: lesional FP1/FP2, Cathode: non-lesional C3/C4), or bihemispheric (Anode: lesional C3/C4, Cathode: non-lesional C3/C4). We collected MEP size, short intracortical inhibition (SICI, 3 ms) and intracortical facilitation (ICF, 15 ms) on bilateral abductor pollicis brevis (APB) muscles using single or paired pulse TMS at 5 timepoints (baseline and four post-tDCS 12 minutes apart sessions).

Results: All 18 subjects had comparable resting motor threshold (rMT) across 3 montages (see A). Bihemispheric tDCS montage offered significantly larger peak-to-peak MEP responses on the lesioned cortex (ANOVA, F=8.97, P<0.01) but not on the non-lesioned cortex (ANOVA, F=0.86, P=0.42). These differences were apparent in single pulse, SICI and ICF (see B).

Conclusion: Our findings support that bihemispheric montage is better suited in post-stroke motor recovery tDCS applications.

National Institutes of Health StrokeNet Training Core

Background and Purpose- The National Institutes of Health (NIH) StrokeNet provides a nationwide infrastructure to advance stroke research. Capitalizing on this unique opportunity, the NIH StrokeNet Training Core (NSTC) was established with the overarching goal of enhancing the professional development of a diverse spectrum of professionals who are embedded in the stroke clinical trials network of the NIH StrokeNet. Methods- This special report provides a descriptive account of the rationale, organization, and activities of the NSTC since its inception in 2013. Current processes and their evolution over time for facilitating training of NIH StrokeNet trainees have been highlighted. Data collected for monitoring training are summarized. Outcomes data (publications and grants) collected by NSTC was supplemented by publicly available resources. Results- The NSTC comprises of cross-network faculty, trainees, and education coordinators. It helps in the development and monitoring of training programs and organizes educational and career development activities. Trainees are provided directed guidance towards their mandated research projects, including opportunities to present at the International Stroke Conference. The committee has focused on developing sustainable models of peer-to-peer interaction and cross-institutional mentorships. A total of 124 professionals (43.7% female, 10.5% underrepresented minorities) have completed training between 2013 and 2018, of whom 55% were clinical vascular neurologists. Of the total, 85% transitioned to a formal academic position and 95% were involved in stroke research post-training. Altogether, 1659 indexed publications have been authored or co-authored by NIH StrokeNet Trainees, of which 58% were published during or after their training years. Based on data from 109 trainees, 33% had submitted 72 grant proposals as principal or co-principal investigators of which 22.2% proposals have been funded. Conclusions- NSTC has provided a foundation to foster nationwide training in stroke research. Our data demonstrate strong contribution of trainees towards academic scholarship. Continued innovation in educational methodologies is required to adapt to unique training opportunities such as the NIH StrokeNet.

Mesenchymal Stem Cell Therapy in Stroke: A Systematic Review of Literature in Pre-Clinical and Clinical Research

Exogenous stem cell therapy (SCT) has been recognized recently as a promising neuroregenerative strategy to augment recovery in stroke survivors. Mesenchymal stem cells (MSCs) are the primary source of stem cells used in the majority of both pre-clinical and clinical studies in stroke. In the absence of evidence-based guidelines on the use of SCT in stroke patients, understanding the progress of MSC research across published studies will assist researchers and clinicians in better achieving success in translating research. We conducted a systematic review on published literature using MSCs in both pre-clinical studies and clinical trials between 2008 and 2017 using the public databases PubMed and Ovid Medline, and the clinical trial registry ( www.clinicaltrials.gov ). A total of 78 pre-clinical studies and eight clinical studies were identified. While majority of the pre-clinical and clinical studies demonstrated statistically significant effects, the clinical significance of these findings was still unclear. Effect sizes could not be measured mainly due to reporting issues in pre-clinical studies, thus limiting our ability to compare results across studies quantitatively. The overall quality of both pre-clinical and clinical studies was sub-optimal. By conducting a systematic review of both pre-clinical and clinical studies on MSCs therapy in stroke, we assessed the quality of current evidence and identified several issues and gaps in translating animal studies to human trials. Addressing these issues and incorporating changes into future animal studies and human trials may lead to better success of stem cells-based therapeutics in the near future.

Evidence of transcranial direct current stimulation-generated electric fields at subthalamic level in human brain in vivo

BACKGROUND

Transcranial direct current stimulation (tDCS) is a promising brain modulation technique for several disease conditions. With this technique, some portion of the current penetrates through the scalp to the cortex and modulates cortical excitability, but a recent human cadaver study questions the amount. This insufficient intracerebral penetration of currents may partially explain the inconsistent and mixed results in tDCS studies to date. Experimental validation of a transcranial alternating current stimulation-generated electric field (EF) in vivo has been performed on the cortical (using electrocorticography, ECoG, electrodes), subcortical (using stereo electroencephalography, SEEG, electrodes) and deeper thalamic/subthalamic levels (using DBS electrodes). However, tDCS-generated EF measurements have never been attempted.

OBJECTIVE

We aimed to demonstrate that tDCS generates biologically relevant EF as deep as the subthalamic level in vivo.

METHODS

Patients with movement disorders who have implanted deep brain stimulation (DBS) electrodes serve as a natural experimental model for thalamic/subthalamic recordings of tDCS-generated EF. We measured voltage changes from DBS electrodes and body resistance from tDCS electrodes in three subjects while applying direct current to the scalp at 2 mA and 4 mA over two tDCS montages.

RESULTS

Voltage changes at the level of deep nuclei changed proportionally with the level of applied current and varied with different tDCS montages.

CONCLUSIONS

Our findings suggest that scalp-applied tDCS generates biologically relevant EF. Incorporation of these experimental results may improve finite element analysis (FEA)-based models.

Abstract WP139: Transcranial Direct Current Stimulation (tDCS) Generates Electric Fields (EF) at the Level of Deep Nuclei of the Human Brain in vivo

Introduction: tDCS is an investigational neuromodulatory therapy for stroke recovery and data has been inconsistent and mixed. The general perception for tDCS is that the majority of current gets shunted at the level of scalp and only minor portion penetrates to the superficial cortex. We aimed to detect electrical field (EF) via deep brain stimulation (DBS) leads in human brain.

Hypothesis: Scalp-applied tDCS generates EF across the brain and forms detectable voltage gradient across DBS leads.

Methods: We recruited patients undergoing DBS stage 2 procedure (implantable pulse generator or IPG implantation). We connected our recording setup to the IPG end of the DBS lead(s), which is otherwise unavailable except this specific surgical procedure. We applied 2 mA and 4 mA of tDCS using bitemporal and occipitofrontal montage and recorded voltage gradients across electrodes of DBS lead(s), while monitoring the applied voltage, injected current and body resistance through tDCS setup.

Results: We recruited 3 patients with unilateral or bilateral DBS leads and found that tDCS application results in changed voltage gradient across contact points of the leads. Because of side-by-side orientation of the leads, bitemporal montage induces in voltage gradient in dose-dependent manner, but occipitofrontal montage did not detect any voltage gradient across the DBS leads because of their relatively equidistant positioning from the anode/cathode. Finally, 4 mA of tDCS resulted in lower body resistance (~20-30% less) when compared to 2 mA of tDCS.

Conclusions: tDCS-generated EF were detected at the level of deep nuclei. Our findings offer insights into the body’s changing resistance to tDCS in a dose-dependent manner that can optimize tDCS simulation models towards improving tDCS efficacy in stroke recovery.

Mobile health as a viable strategy to enhance stroke risk factor control: A systematic review and meta-analysis

BACKGROUND

With the rapid growth worldwide in cell-phone use, Internet connectivity, and digital health technology, mobile health (mHealth) technology may offer a promising approach to bridge evidence-treatment gaps in stroke prevention. We aimed to evaluate the effectiveness of mHealth for stroke risk factor control through a systematic review and meta-analysis.

METHODS

We searched PubMed from January 1, 2000 to May 17, 2016 using the following keywords: mobile health, mHealth, short message, cellular phone, mobile phone, stroke prevention and control, diabetes mellitus, hypertension, hyperlipidemia and smoking cessation. We performed a meta-analysis of all eligible randomized control clinical trials that assessed a sustained (at least 6months) effect of mHealth.

RESULTS

Of 78 articles identified, 13 met eligibility criteria (6 for glycemic control and 7 for smoking cessation) and were included for the final meta-analysis. There were no eligible studies for dyslipidemia or hypertension. mHealth resulted in greater Hemoglobin A1c reduction at 6months (6 studies; 663 subjects; SMD: -0.44; 95% CI: [-0.82, -0.06], P=0.02; Mean difference of decrease in HbA1c: -0.39%; 95% CI: [-0.74, -0.04], P=0.03). mHealth also lead to relatively higher smoking abstinence rates at 6months (7 studies; 9514 subjects; OR: 1.54; 95% CI: [1.24, 1.90], P<0.0001).

CONCLUSIONS

Our meta-analysis supports that use of mHealth improves glycemic control and smoking abstinence rates.

Safety and tolerability of transcranial direct current stimulation to stroke patients - A phase I current escalation study

BACKGROUND AND OBJECTIVE

A prior meta-analysis revealed that higher doses of transcranial direct current stimulation (tDCS) have a better post-stroke upper-extremity motor recovery. While this finding suggests that currents greater than the typically used 2 mA may be more efficacious, the safety and tolerability of higher currents have not been assessed in stroke patients. We aim to assess the safety and tolerability of single session of up to 4 mA in stroke patients.

METHODS

We adapted a traditional 3 + 3 study design with a current escalation schedule of 1»2»2.5»3»3.5»4 mA for this tDCS safety study. We administered one 30-min session of bihemispheric montage tDCS and simultaneous customary occupational therapy to patients with first-ever ischemic stroke. We assessed safety with pre-defined stopping rules and investigated tolerability through a questionnaire. Additionally, we monitored body resistance and skin temperature in real-time at the electrode contact site.

RESULTS

Eighteen patients completed the study. The current was escalated to 4 mA without meeting the pre-defined stopping rules or causing any major safety concern. 50% of patients experienced transient skin redness without injury. No rise in temperature (range 26°C-35 °C) was noted and skin barrier function remained intact (i.e. body resistance >1 kΩ).

CONCLUSION

Our phase I safety study supports that single session of bihemispheric tDCS with current up to 4 mA is safe and tolerable in stroke patients. A phase II study to further test the safety and preliminary efficacy with multi-session tDCS at 4 mA (as compared with lower current and sham stimulation) is a logical next step. ClinicalTrials.gov Identifier: NCT02763826.

Abstract TP68: The Characteristics of Acute Ischemic Stroke Treatment Clinical Trials Over the Past Twenty Years: Implications for Future Trial Design

Introduction: There was a 20 years span between the landmark NINDS r-tPA trials and the recent spate of positive endovascular trials of acute ischemic stroke. The evolution of clinical trial design, characteristics of subjects, and nature of background standard care have not been properly studied. Such information could have consequences for future clinical trial designs.

Objective: To systematically search the literature for randomized controlled trials of acute ischemic stroke and identify key patterns.

Methods: We interrogated Pubmed from 1995 to 2015 with MeSH terms (Fig 1A). Inclusion criteria are: 1) acute intervention delivered within 24 hours of onset; 2) randomized trial with a control (either placebo or standard care) group with ≥20 subjects in each arm; 3) mRS used as an outcome at 3 months; 4) published in the English language. Data were extracted and effect sizes were calculated for both mortality and favorable outcome (mRS: 0-1). We also extracted data for baseline characteristics and analyzed trends over time.

Results: Forty-six clinical trials were included with 19951 subjects and 38.5% of them were females. There were 8 phase II and 11 phase III trials, nine out of 46 are positive trials . Average number of subjects per trial was 443 and number of patient enrollments per year ranged from 23-270. Study-wise odd’s ratio ranged 0.15 - 3.97 for mortality and 0.30- 3.06 for favorable outcomes. Rate of mortality was 13.6% (0-44%) and favorable outcomes ranged 6-37% in control and 7.5-74.8% in intervention arm. Median onset of treatment ranged from 90 - 972 minutes. There are trends of increased NIHSS score at baseline for studies over the years. The type of intervention and baseline NIHSS are major determinants of mortality rate.

Conclusions: Patterns existed in the acute ischemic stroke treatment trials. Understanding these patterns may inform the stroke community to better design trials in the future.

Abstract 100: A Simple Bedside Grading Scale Can Effectively Predict Severe Post-stroke Upper-extremity Spasticity

Introduction: Upper-limb spasticity is a very disabling complication after stroke. There has been no simple clinical standard scale to predict spasticity immediately after stroke. This study aims to develop a simple bedside grading scale with the information collected during the acute phase to predict spasticity at 3 month post-stroke

Methods: This is a prospective cohort study (Prediction and Imaging Biomarker of Post-stroke Motor Recovery) of patients with first-ever acute ischemic stroke with various degrees of motor impairment. NIH stroke scale (NIHSS) was assessed 2-7 days after onset of stroke symptoms. Modified Ashworth Spasticity Scale was used as an assessment tool in biceps, wrist flexors and finger flexors at 90 days (± 15 days) and score ≥2 at any muscle was considered as severe spasticity. Infarction volume was measured based on the lesion on MRI/DWI. Independent predictors of upper-limb spasticity at 90 days were identified by multivariate logistic regression. A risk stratification scale was developed with weighting independent predictors based on beta coefficient.

Results: One hundred twenty three patients were recruited for this study. Covariates associated with upper-limb spasticity are NIHSS arm score (p<0.0001), sub-cortical location (p=0.004) and lesion volume >65 cc (p=0.025). The proposed grading scale is summation of individual points as followed: NIHSS Arm Score: =4 (2 point), <4 (0 point); infarct location: sub-cortical (1 point), non sub-cortical (0 point); infarct volume: ≥65 cc (1 point), <65cc (0 point). The rates of severe upper limb spasticity for the bedside spasticity scale, in order 0-4, are 8.9%, 29.2%, 65%, 88.7%, 96.2%. In other words, the likelihood of developing severe spasticity increases steadily using the score.

Conclusion: A simple bedside grading scale can effectively predict severe post-stroke upper-limb spasticity at 90 days. Validation with an independent external dataset is a planned next step.

Abstract 103: A Phase I Current Escalation Study for Transcranial Direct Current Stimulation in Ischemic Stroke Patients

Introduction: Positive dose-response relationship with the use of Transcranial direct current stimulation (tDCS) in post-stroke upper limb motor recovery demands investigating the efficacy of higher tDCS doses. Safety and tolerability of tDCS current higher than typically used 2 mA has not been investigated in stroke patients.

Hypothesis: tDCS application up to 4 mA for 30 minutes is safe and tolerable in stroke patients

Methods: A 3+3 study design with current escalation schedule of 1, 2, 2.5, 3, 3.5 and 4 mA was adopted for this tDCS safety study ( Fig. A ). Patients with first-ever ischemic stroke and unilateral hemiparesis were recruited. Single session of tDCS and customatory occupational therapy for 30 minutes using a device (Chattanooga Ionto) with 5х7 cm 2 sponge electrodes (Soterix Medical) on a bihemispheric montage (C3/C4, anode on lesional side) were administered. Stopping rules were (1) second degree scalp burn, or (2) seizure, or (3) new lesion(s) on DWI sequence of MRI or decreased ADC. Tolerability was assessed by tDCS questionnaire administered before and after tDCS. Body resistance and skin temperature at electrode contact site were monitored in real time.

Results: Eighteen patients were enrolled and completed the study. The current was escalated to 4 mA without any major safety concerns (stopping rule). 50% of patients revealed transient skin redness at anodal site and 17% at cathodal side. No patient had any persistent skin perception issues at the end of tDCS ( Fig. B ). We also present real-time monitoring of body resistance and skin temperature to ensure safety during tDCS administration ( Fig. C ). Skin barrier remained intact through tDCS, as demonstrated by absence of abrupt decrease in body resistance (<400 Ω). Skin temperatures remained well below body temperature (range 26°C-35°C)

Conclusion: Our data support that tDCS current up to 4 mA is safe and tolerable in ischemic stroke patients. Efficacy and safety should be further tested in a phase II study.

Abstract TMP13: Safety and Efficacy of Lower Dose versus Standard Dose r-tPA: A Meta-Analysis

Introduction: Intravenous r-tPA at a dose of 0.9 mg/kg of body weight is an established effective treatment for acute ischemic stroke with increased risk for symptomatic intracranial hemorrhage(sICH); however, r-tPA at dose <0.9 mg/kg has been investigated in different studies with mixed results in terms of safety and efficacy. We aimed to conduct a meta-analysis on existing clinical trials that compare the standard dose (0.9 mg/kg) with the low-dose group.

Hypothesis: Patients receiving intravenous low dose r-tPA will have equivalent favorable outcomes, lower risk of sICH and mortality rate as compared with standard dose.

Methods: We searched Pubmed from 1992 to 2015 with terms of “low dosage”, “tPA” and “ischemic stroke” (Fig 1A). Inclusion criteria are: 1) randomized or non-randomized studies with two arms (0.9 mg/kg vs. <0.9 mg/kg); 2) mortality was available in the manuscript; 3) modified Rankin Scale(mRS) was used as the primary or secondary outcome at 3 months; 4) published in English language. Data were extracted and summary odds ratios were calculated for sICH, the mortality rate, favorable outcome (mRS of 0-1).

Results: Ten clinical studies met inclusion criteria and were included with 14,321 subjects among which 43.7% were females. Low-dose groups ranged from 0.5 to 0.85 mg/kg. The summary odds ratio for low-dose group vs. standard dose group is 1.02 [0.36-2.85, p=0.97] for sICH; 1.20 [0.81-1.78, p=0.65] for mortality rate; 0.88 [0.77-0.95, p=0.004] for favorable outcome at 3 months.

Conclusions: Our results from meta-analysis show that low dose of r-tPA is less likely associated with favorable outcome at 3 months, although the risk of sICH and mortality rate are equivalent as compared with the standard dose group.

Abstract TMP98: Could Mobile Health be an Effective Strategy for Enhancing Stroke Prevention?

Background: The overwhelming majority of strokes can be prevented via optimal vascular risk factor control. However, there remains an evidence practice gap with regard to treatment of vascular risk factors. With the rapid growth worldwide in cell-phone use, Internet connectivity, and digital health technology, mobile health (mHealth) technology may offer a promising approach to bridge these treatment gaps and reduce the global burden of stroke.

Objective: To evaluate the effectiveness of mHealth in vascular risk factor control through a systemic review and meta-analysis.

Methods: We searched PubMed from January 1, 2000 to May 17, 2016 using keywords: mobile health, mhealth, short message, cellular phone, mobile phone, stroke prevention and control, diabetes mellitus, hypertension, hyperlipidemia and smoking cessation. We performed a meta-analysis of all eligible randomized control clinical trials that assessed the long-term (at 6 months) effect of mHealth.

Results: Of 79 articles identified, 13 of them met eligibility criteria (6 for glycemic control and 7 for smoking cessation) and were included for the final meta-analysis. There were no eligible studies for dyslipidemia or hypertension. mHealth resulted in greater HbA1c reduction at 6 months (6 studies; 663 subjects; SMD: -0.44; 95% CI: [-0.82, -0.06], P =0.02; Mean difference of decrease in HbA1c: -0.39%; 95% CI: [-0.74,-0.04], P =0.03). mHealth also led to relatively higher smoking abstinence rates at 6 months (7 studies; 9,514 subjects; OR: 1.54; 95% CI: [1.24, 1.90], P <0.0001).

Conclusion: Use of mHealth improves glycemic control and smoking abstinence rates, two factors that may lead to better stroke outcomes. Future mHealth studies should focus on modifying premier vascular risk factors like hypertension, specifically in people with or at risk of stroke.

Neural correlates of single-vessel haemodynamic responses in vivo

Neural activation increases blood flow locally. This vascular signal is used by functional imaging techniques to infer the location and strength of neural activity. However, the precise spatial scale over which neural and vascular signals are correlated is unknown. Furthermore, the relative role of synaptic and spiking activity in driving haemodynamic signals is controversial. Previous studies recorded local field potentials as a measure of synaptic activity together with spiking activity and low-resolution haemodynamic imaging. Here we used two-photon microscopy to measure sensory-evoked responses of individual blood vessels (dilation, blood velocity) while imaging synaptic and spiking activity in the surrounding tissue using fluorescent glutamate and calcium sensors. In cat primary visual cortex, where neurons are clustered by their preference for stimulus orientation, we discovered new maps for excitatory synaptic activity, which were organized similarly to those for spiking activity but were less selective for stimulus orientation and direction. We generated tuning curves for individual vessel responses for the first time and found that parenchymal vessels in cortical layer 2/3 were orientation selective. Neighbouring penetrating arterioles had different orientation preferences. Pial surface arteries in cats, as well as surface arteries and penetrating arterioles in rat visual cortex (where orientation maps do not exist), responded to visual stimuli but had no orientation selectivity. We integrated synaptic or spiking responses around individual parenchymal vessels in cats and established that the vascular and neural responses had the same orientation preference. However, synaptic and spiking responses were more selective than vascular responses--vessels frequently responded robustly to stimuli that evoked little to no neural activity in the surrounding tissue. Thus, local neural and haemodynamic signals were partly decoupled. Together, these results indicate that intrinsic cortical properties, such as propagation of vascular dilation between neighbouring columns, need to be accounted for when decoding haemodynamic signals.

Abstract 74: An Update on Meta-analysis of Transcranial Direct Current Stimulation in Post-stroke Motor Recovery

Introduction: Prior meta-analyses have demonstrated positive summary effect of tDCS on Fugl-Meyer upper extremity scores (FM-UE) improvement as well as dose-response relationship. With new published manuscripts, we are not sure whether this positive effect still holds.

Hypothesis: tDCS leads to better improvements in post-stroke motor recovery when compared to sham, and in a dose-dependent manner.

Methods: We identified sham-controlled, randomized studies with ≥5 tDCS sessions from PubMed until July 2015. We derived effect size as standardized mean differences (Hedge’s g) of change scores, defined as FM-UE improvements. We calculated summary effect size by using random effect model, taking any data heterogeneity into account. We plotted current, charge (current х duration), total charge (charge х sessions) and their density counterparts (by dividing each with pad size). To assess the dose-response relationship, inverse-variance-based meta-regression was performed.

Results: We identified 9 studies with 234 subjects comparing active stimulation (anodal, cathodal or bihemispheric) with sham stimulation against FM-UE change scores. Stroke patients receiving tDCS improved significantly better than sham (summary Hedge’s g = 0.65, 95% CI = [0.18, 1.13], p = 0.03), with superior results in patients with chronic stroke (average time since stroke >2 years, summary Hedge’s g = 1.11, 95% CI = [0.43, 1.83], p = 0.001) than those with acute stroke (average time since stroke <2 months, summary Hedge’s g = 0.18, 95% CI = [-0.30, 0.66], p = 0.47). Dose-response relationship showed that FM-UE change scores correlated positively with charge density (R2 = 0.20, p = 0.036) and negatively with pad size (smaller the pad, better the effect; R2 = 0.58, p = 0.002).

Conclusion: This updated meta-analysis supports that tDCS leads to better improvement in UE motor outcome than with sham, especially in patients with chronic stroke.

Abstract WMP55: Racial Disparities in Stroke Recovery: a Meta-analysis

Introduction: While it is well known that Blacks have a higher risk of death after an index stroke compared to their White counterparts, the influence of Black race on recovery after a stroke is unclear.

Objective: To qualitatively and quantitatively examine the association of Black vs. White race on stroke recovery utilizing a systematic review and meta-analysis.

Methods: We searched PubMed for cohort studies that investigated racial variation issues in stroke motor recovery between January 1970 and July 2015, in which outcome was measured by Functional Independence Measures (FIM) scale. Change scores (the difference score between discharge and admission) or endpoint scores (at the time of discharge) were compared between Whites and Blacks by calculating standardized mean differences (Hedge’s g ) to derive a summary effect size. Random Effects model was used to account for data heterogeneity.

Results: We identified six studies (4 studies with changes scores and 4 studies with endpoint scores available) with a total 151,361 subjects. Overall, there was no difference between blacks vs. Whites (Hedge’s g = 0.02, 95% CI = [-0.08, 0.13], p = 0.89) if endpoint scores were used, but Whites seemed to show a non-significant pattern of greater improvement than Blacks during the inpatient hospital rehabilitation (FIM change scores, Hedge’s g = 0.12, 95% CI = [-0.05, 0.30], p = 0.17). This qualitative discrepancy maybe explained by the difference in admission score between the two groups (Hedge’s g = 0.16, 95% CI = [-0.01, 0.34], p = 0.06). Better FIM change scores in Whites maybe explained by longer stays in hospital (Hedge’s g = 0.13, 95% CI = [0.00, 0.25], p = 0.06).

Conclusions: This analysis identifies a significant evidence gap for racial disparities in stroke recovery. Additional studies to assess change scores are needed to address these gaps.

Abstract 72: A Novel VLSM-CST Lesion Load Model is a Superior Predictor of Motor Outcomes of Acute Stroke Patients

Introduction: Lesion load of the Corticospinal Tract (CST-LL) can predict 64% of the variance in 3-months outcome of acute stroke patients. Voxel-based lesion symptom mapping (VLSM) studies have revealed brain voxels associated with motor impairment. A combined VLSM- CST-LL approach may give particular weight to voxels that are both part of an impairment map and the descending motor tracts.

Hypothesis: A combined VLSM-wCST-LL model can predict acute motor outcome better than weighted CST-LL alone.

Methods: We derived the VLSM map from a group of 50 chronic patients with variable motor deficits relating voxels of patients’ lesions to Upper Extremity Fugl-Meyer (UE-FM) scores. A correction for multiple comparisons was applied at FDR<0.05. Resulting VLSM T-maps were multiplied using our probabilistic CST maps, and then summed to form a canonical VLSM-weighted CST tract. Individual lesion maps from 76 acute stroke patients were overlaid onto the VLSM-weighted CST map to calculate lesion load. Patients were assessed for motor impairment (UE-FM) at baseline and at 3 months. Linear regressions were fit for baseline UE-FM, wCST-LL, and Days-of-Therapy (DoT) to determine predictions of 3-months outcome. A multivariate regression was run using VSLM-weighted CST-LL, controlling for baseline UE-FM and DoT. Age was not a significant regressor. Akaike Information Criterion was run to select the best fit model.

Results: The VLSM analysis determined that voxels of lesions in the precentral gyrus, premotor regions, the corona radiata region, and within the descending motor tracts were significantly related to chronic motor impairment. VLSM-CST-LL applied to a group of acute stroke patients with motor impairment predicted 85% of the variance at 3 months motor outcome. AIC results confirmed with 99% certainty that VLSM is the best fit model.

Conclusions: VLSM-weighted CST-LL is the superior fit model compared to the weighted CST-LL model for predicting 3 months outcome.

Corticospinal tract lesion load: An imaging biomarker for stroke motor outcomes

OBJECTIVE

The aim of this work was to investigate whether an imaging measure of corticospinal tract (CST) injury in the acute phase can predict motor outcome at 3 months in comparison to clinical assessment of initial motor impairment.

METHODS

A two-site prospective cohort study followed up a group of first-ever ischemic stroke patients using the Upper-Extremity Fugl-Meyer (UE-FM) Scale to measure motor impairment in the acute phase and at 3 months. A weighted CST lesion load (wCST-LL) was calculated by overlaying the patient's lesion map on magnetic resonance imaging with a probabilistic CST constructed from healthy control subjects. Regression models were fit to assess the predictive value of wCST-LL and compared with initial motor impairment.

RESULTS

Seventy-six patients (37 from cohort 1 and 39 from cohort 2) completed the study. wCST-LL as well as assessment of motor impairment (UE-FM) in the acute phase correlated with motor impairment (UE-FM) at 3 months in both cohort 1 (R(2)  = 0.69 vs. R(2)  = 0.67; p = 0.43) and cohort 2 (R(2)  = 0.69 vs. R(2)  = 0.62; p = 0.25). In the severely impaired subgroup (defined as UE-FM ≤ 10 at baseline), wCST-LL correlated with outcomes significantly better than clinical assessment (R(2)  = 0.47 vs. R(2)  = 0.11; p = 0.03). In the nonseverely impaired subgroup, stroke patients recovered approximately 70% of their maximal recovery potential. All stroke patients in both cohorts had poor motor outcomes at 3 months (defined as UE-FM ≤ 25) when wCST-LL was ≥ 7.0 cc (positive predictive value was 100%).

INTERPRETATION

wCST-LL, an imaging biomarker determined in the acute phase, can predict poststroke motor outcomes at 3 months, especially in patients with severe impairment at baseline.

Transcranial Direct Current Stimulation Post-Stroke Upper Extremity Motor Recovery Studies Exhibit a Dose-Response Relationship

BACKGROUND AND PURPOSE

Transcranial direct current stimulation (tDCS) has shown mixed results in post-stroke motor recovery, possibly because of tDCS dose differences. The purpose of this meta-analysis was to explore whether the outcome has a dose-response relationship with various dose-related parameters.

METHODS

The literature was searched for double-blind, randomized, sham-controlled clinical trials investigating the role of tDCS (≥5 sessions) in post-stroke motor recovery as measured by the Fugl-Meyer Upper Extremity (FM-UE) scale. Improvements in FM-UE scores were compared between active and sham groups by calculating standardized mean differences (Hedge's g) to derive a summary effect size. Inverse-variance-weighted linear meta-regression across individual studies was performed between various tDCS parameters and Hedge's g to test for dose-response relationships.

RESULTS

Eight studies with total of 213 stroke subjects were included. Summary Hedge's g was statistically significant in favor of the active group (Hedge's g = 0.61, p = 0.02) suggesting moderate effect. Specifically, studies that used bihemispheric tDCS montage (Hedge's g = 1.30, p = 0.08) or that recruited chronic stroke patients (Hedge's g = 1.23, p = 0.02) showed large improvements in the active group. A positive dose-response relationship was found with current density (p = 0.017) and charge density (p = 0.004), but not with current amplitude. Moreover, a negative dose-response relationship was found with electrode size (p < 0.001, smaller electrodes were more effective).

CONCLUSIONS

Our meta-analysis and meta-regression results suggest superior motor recovery in the active group when compared to the sham group and dose-response relationships relating to electrode size, charge density and current density. These results need to be confirmed in future dedicated studies.

Improved blood velocity measurements with a hybrid image filtering and iterative Radon transform algorithm

Neural activity leads to hemodynamic changes which can be detected by functional magnetic resonance imaging (fMRI). The determination of blood flow changes in individual vessels is an important aspect of understanding these hemodynamic signals. Blood flow can be calculated from the measurements of vessel diameter and blood velocity. When using line-scan imaging, the movement of blood in the vessel leads to streaks in space-time images, where streak angle is a function of the blood velocity. A variety of methods have been proposed to determine blood velocity from such space-time image sequences. Of these, the Radon transform is relatively easy to implement and has fast data processing. However, the precision of the velocity measurements is dependent on the number of Radon transforms performed, which creates a trade-off between the processing speed and measurement precision. In addition, factors like image contrast, imaging depth, image acquisition speed, and movement artifacts especially in large mammals, can potentially lead to data acquisition that results in erroneous velocity measurements. Here we show that pre-processing the data with a Sobel filter and iterative application of Radon transforms address these issues and provide more accurate blood velocity measurements. Improved signal quality of the image as a result of Sobel filtering increases the accuracy and the iterative Radon transform offers both increased precision and an order of magnitude faster implementation of velocity measurements. This algorithm does not use a priori knowledge of angle information and therefore is sensitive to sudden changes in blood flow. It can be applied on any set of space-time images with red blood cell (RBC) streaks, commonly acquired through line-scan imaging or reconstructed from full-frame, time-lapse images of the vasculature.

Towards a naturalistic brain-machine interface: hybrid torque and position control allows generalization to novel dynamics

Realization of reaching and grasping movements by a paralytic person or an amputee would greatly facilitate her/his activities of daily living. Towards this goal, control of a computer cursor or robotic arm using neural signals has been demonstrated in rodents, non-human primates and humans. This technology is commonly referred to as a Brain-Machine Interface (BMI) and is achieved by predictions of kinematic parameters, e.g. position or velocity. However, execution of natural movements, such as swinging baseball bats of different weights at the same speed, requires advanced planning for necessary context-specific forces in addition to kinematic control. Here we show, for the first time, the control of a virtual arm with representative inertial parameters using real-time neural control of torques in non-human primates (M. radiata). We found that neural control of torques leads to ballistic, possibly more naturalistic movements than position control alone, and that adding the influence of position in a hybrid torque-position control changes the feedforward behavior of these BMI movements. In addition, this level of control was achievable utilizing the neural recordings from either contralateral or ipsilateral M1. We also observed changed behavior of hybrid torque-position control under novel external dynamic environments that was comparable to natural movements. Our results demonstrate that inclusion of torque control to drive a neuroprosthetic device gives the user a more direct handle on the movement execution, especially when dealing with novel or changing dynamic environments. We anticipate our results to be a starting point of more sophisticated algorithms for sensorimotor neuroprostheses, eliminating the need of fully automatic kinematic-to-dynamic transformations as currently used by traditional kinematic-based decoders. Thus, we propose that direct control of torques, or other force related variables, should allow for more natural neuroprosthetic movements by the user.

An artery-specific fluorescent dye for studying neurovascular coupling

We demonstrate that Alexa Fluor 633 hydrazide (Alexa Fluor 633) selectively labels neocortical arteries and arterioles by binding to elastin fibers. We measured sensory stimulus-evoked arteriole dilation dynamics in mouse, rat and cat visual cortex using Alexa Fluor 633 together with neuronal activity using calcium indicators or blood flow using fluorescein dextran. Arteriole dilation decreased fluorescence recorded from immediately underlying neurons, representing a potential artifact during neuronal functional imaging experiments.

Comparison of force and power generation patterns and their predictions under different external dynamic environments

Use of neural activity to predict kinematic variables such as position, velocity and direction etc of movements has been implemented in real-time control of robotic systems and computer cursors. In everyday life, however, we generate variable amounts of force to manipulate objects of different inertial properties or to follow the same trajectory under different external dynamic environments like air or water. The resultant work during such movements, and its time derivative power, should depend on the dynamics of the movement. In order to give the users of a brain-machine interface (BMI) comprehensive control of a prosthetic limb under different dynamic conditions, it is imperative to consider the dynamics-related parameters like end-effector forces, joint torques or power. In this paper, we show distribution patterns of two such dynamics parameters - force and power - and their predictive efficiency under different dynamic environmental conditions. We intend to find the force-related parameter, which has optimal predictive efficiency across different dynamic environments that is generalization. Our ultimate goal is to materialize a force-based brain-machine interface (fBMI).

A bio-friendly and economical technique for chronic implantation of multiple microelectrode arrays

Many neurophysiological experiments on rodents and non-human primates involve the implantation of more than one multi-electrode array to record from many regions of the brain. So called 'floating' microelectrode arrays are implanted in cortical regions of interest and are coupled via a flexible cable to their connectors which are fixed to the skull by a cement cap or a titanium pedestal, such as the Cereport system, which has been approved for human use. The use of bone cement has several disadvantages including the creation of infection prone areas at the interface with the skull and surrounding skin. Alternatively, the more biocompatible Cereport has a limited carrying capacity and is far more expensive. In this paper, we describe a new implantation technique, which combines the biocompatibility of titanium, a high carrying capacity with a minimal skull footprint, and a decreased chance of infection, all in a relatively inexpensive package. This technique utilizes an in-house fabricated 'Nesting Platform' (NP), mounted on a titanium headpost to hold multiple connectors above the skin, making the headpost the only transcutaneous object. The use of delrin, a durable, lightweight and easily machinable material, allows easy customization of the NP for a wide variety of floating electrodes and their connectors. The ultimate result is a longer survival time with superior neural recordings that can potentially last longer than with traditional implantation techniques.