Feasibility of Direct Current stimulation through hair using a dry electrode: potential for transcranial Direct Current Stimulation (tDCS) application.

Conventional transcranial direct current stimulation (tDCS) protocols typically deliver 2 mA for 20-30 minutes. The most common administration uses a wet electrode approach which dries out in ~60 minutes at room temperature. This restricts its application to limited duration electrode-scalp contact use cases unless additional conductive media (saline, gel, or paste) is re-applied. This problem is further compounded by the subject's hair which not only presents administration challenges (interferes with electrode attachment and adhesion) but also acts as a conduit of current flow into the scalp resulting in current hotspots. This non-uniform current injection results in increased skin sensation. The aim of this study was to determine suitability of a commercially available hydrogel for DC delivery through hair. Experiments involved both non-clinical testing on an agar block and clinical testing on subjects' forearms. Electrodes were positioned on the posterior side of the forearm that has hair for the clinical testing. Typical dose as used in tDCS was delivered and pain scores were collected. Results indicate suitable current delivery performance and all subjects tolerated delivery with pain scores ranging between 0-6. Our study paves the way for future testing on the scalp for tDCS application.Clinical Relevance-This study demonstrates the possibility of delivering tDCS through hair via dry electrodes. Specific use cases that cannot use a traditional wet electrode approach stand to benefit from the results of our work.

Elevated glucose and oligomeric ß-amyloid disrupt synapses via a common pathway of aberrant protein S-nitrosylation.

Metabolic syndrome (MetS) and Type 2 diabetes mellitus (T2DM) increase risk for Alzheimer's disease (AD). The molecular mechanism for this association remains poorly defined. Here we report in human and rodent tissues that elevated glucose, as found in MetS/T2DM, and oligomeric ß-amyloid (Aß) peptide, thought to be a key mediator of AD, coordinately increase neuronal Ca(2+) and nitric oxide (NO) in an NMDA receptor-dependent manner. The increase in NO results in S-nitrosylation of insulin-degrading enzyme (IDE) and dynamin-related protein 1 (Drp1), thus inhibiting insulin and Aß catabolism as well as hyperactivating mitochondrial fission machinery. Consequent elevation in Aß levels and compromise in mitochondrial bioenergetics result in dysfunctional synaptic plasticity and synapse loss in cortical and hippocampal neurons. The NMDA receptor antagonist memantine attenuates these effects. Our studies show that redox-mediated posttranslational modification of brain proteins link Aß and hyperglycaemia to cognitive dysfunction in MetS/T2DM and AD.

Evaluation of Dry Sensors for Neonatal EEG Recordings.

PURPOSE: Neonatal seizures are a common neurologic diagnosis in neonatal intensive care units, occurring in approximately 14,000 newborns annually in the United States. Although the only reliable means of detecting and treating neonatal seizures is with an electroencephalography (EEG) recording, many neonates do not receive an EEG or experience delays in getting them. Barriers to obtaining neonatal EEGs include (1) lack of skilled EEG technologists to apply conventional wet electrodes to delicate neonatal skin, (2) poor signal quality because of improper skin preparation and artifact, and (3) extensive time needed to apply electrodes. Dry sensors have the potential to overcome these obstacles but have not previously been evaluated on neonates. METHODS: Sequential and simultaneous recordings with wet and dry sensors were performed for 1 hour on 27 neonates from 35 to 42.5 weeks postmenstrual age. Recordings were analyzed for correlation and amplitude and were reviewed by neurophysiologists. Performance of dry sensors on simulated vernix was examined. RESULTS: Analysis of dry and wet signals showed good time-domain correlation (reaching >0.8), given the nonsuperimposed sensor positions and similar power spectral density curves. Neurophysiologist reviews showed no statistically significant difference between dry and wet data on most clinically relevant EEG background and seizure patterns. There was no skin injury after 1 hour of dry sensor recordings. In contrast to wet electrodes, impedance and electrical artifact of dry sensors were largely unaffected by simulated vernix. CONCLUSIONS: Dry sensors evaluated in this study have the potential to provide high-quality, timely EEG recordings on neonates with less risk of skin injury.

High-frequency hippocampal oscillations activated by optogenetic stimulation of transplanted human ESC-derived neurons.

After transplantation, individual stem cell-derived neurons can functionally integrate into the host CNS; however, evidence that neurons derived from transplanted human embryonic stem cells (hESCs) can drive endogenous neuronal network activity in CNS tissue is still lacking. Here, using multielectrode array recordings, we report activation of high-frequency oscillations in the ß and γ ranges (10-100 Hz) in the host hippocampal network via targeted optogenetic stimulation of transplanted hESC-derived neurons.

Electrophysiological mapping of embryonic mouse hearts: mechanisms for developmental pacemaker switch and internodal conduction pathway.

INTRODUCTION: Understanding sinoatrial node (SAN) development could help in developing therapies for SAN dysfunction. However, electrophysiological investigation of SAN development remains difficult because mutant mice with SAN dysfunctions are frequently embryonically lethal. Most research on SAN development is therefore limited to immunocytochemical observations without comparable functional studies. METHODS AND RESULTS: We applied a multielectrode array (MEA) recording system to study SAN development in mouse hearts acutely isolated at embryonic ages (E) 8.5-12.5 days. Physiological heart rates were routinely restored, enabling accurate functional assessment of SAN development. We found that dominant pacemaking activity originated from the left inflow tract (LIFT) region at E8.5, but switched to the right SAN by E12.5. Combining MEA recordings and pharmacological agents, we show that intracellular calcium (Ca(2+))-mediated automaticity develops early and is the major mechanism of pulse generation in the LIFT of E8.5 hearts. Later in development at E12.5, sarcolemmal ion channels develop in the SAN at a time when pacemaker channels are down-regulated in the LIFT, leading to a switch in the dominant pacemaker location. Additionally, low micromolar concentrations of tetrodotoxin (TTX), a sodium channel blocker, minimally affect pacemaker rhythm at E8.5-E12.5, but suppress atrial activation and reveal a TTX-resistant SAN-atrioventricular node (internodal) pathway that mediates internodal conduction in E12.5 hearts. CONCLUSIONS: Using a physiological mapping method, we demonstrate that differential mechanistic development of automaticity between the left and right inflow tract regions confers the pacemaker location switch. Moreover, a TTX-resistant pathway mediates preferential internodal conduction in E12.5 mouse hearts.

Noncontact ECG system for unobtrusive long-term monitoring.

This paper describes measurements made using an ECG system with QUASAR's capacitive bioelectrodes integrated into a pad system that is placed over a chair. QUASAR's capacitive bioelectrode has the property of measuring bioelectric potentials at a small separation from the body. This enables the measurement of ECG signals through fabric, without the removal of clothing or preparation of skin. The ECG was measured through the subject's clothing while the subject sat in the chair without any supporting action from the subject. The ECG pad system is an example of a high compliance system that places minimal requirements upon the subject and, consequently, can be used to generate a long-term record from ECG segments collected on a daily basis, providing valuable information on long-term trends in cardiac health.

EEG and eye-tracking based measures for enhanced training.

This paper describes a project whose goal was to establish the feasibility of using unobtrusive cognitive assessment methodologies in order to optimize efficiency and expediency of training. QUASAR, EyeTracking, Inc. (ETI), and Safe Passage International (SPI), teamed to demonstrate correlation between EEG and eye-tracking based cognitive workload, performance assessment and subject expertise on X-Ray screening tasks. Results indicate significant correlation between cognitive workload metrics based on EEG and eye-tracking measurements recorded during a simulated baggage screening task and subject expertise and error rates in that same task. These results suggest that cognitive monitoring could be useful in improving training efficiency by enabling training paradigms that adapts to increasing expertise.

QUASAR's QStates cognitive gauge performance in the cognitive state assessment competition 2011.

The Cognitive State Assessment Competition 2011 was organized by the U.S. Air Force Research Laboratory (AFRL) to compare the performance of real-time cognitive state classification software. This paper presents results for QUASAR's data classification module, QStates, which is a software package for real-time (and off-line) analysis of physiologic data collected during cognitive-specific tasks. The classifier's methodology can be generalized to any particular cognitive state; QStates identifies the most salient features extracted from EEG signals recorded during different cognitive states or loads.

Protection of retinal ganglion cells by caspase substrate-binding peptide IQACRG from N-methyl-D-aspartate receptor-mediated excitotoxicity.

PURPOSE: This study investigated whether the enzymatically inactive caspase mimetic IQACRG protects rat retinal ganglion cells (RGCs) from excitotoxic insults. Minimally invasive delivery of the peptide to the retina was explored, and the mechanisms of neuroprotection were elucidated. METHODS: IQACRG was linked to penetratin (P-IQACRG) to facilitate cellular uptake. RGC labeling by biotinylated-P-IQACRG delivered via intravitreal or subconjunctival injection was demonstrated by avidin-biotin chemistry. The authors used histologic and electrophysiological measures to evaluate the neuroprotective potential of P-IQACRG against RGC death induced by N-methyl-D-aspartate (NMDA) in vitro and in vivo. In addition, they monitored activity of an enzyme that is downstream of caspase-1, matrix metalloproteinase-9 (MMP-9), and protein levels of the caspase-3/7 substrate, myocyte enhancer factor 2C (MEF2C), to determine the effectiveness of IQACRG in blocking excessive caspase activity. RESULTS: IQACRG significantly reduced NMDA-induced RGC death in culture and in vivo. Ex vivo electrophysiological recording of the retina on multielectrode arrays demonstrated functional rescue of RGCs by IQACRG. The authors also found that delivery of IQACRG to the retina inhibited NMDA-triggered MMP-9 activity and prevented cleavage of MEF2C protein that would otherwise have been engendered by caspase activation preceding RGC death. Strikingly, subconjunctival injection of P-IQACRG was very effective in preventing NMDA-induced RGC death in vivo. CONCLUSIONS: These data demonstrate that IQACRG protects RGCs from excitotoxicity in vitro and in vivo. The positive results with subconjunctival administration of P-IQACRG suggest that in the future this treatment may be useful clinically in diseases such as glaucoma and retinal ischemia.

Transcription factor MEF2C influences neural stem/progenitor cell differentiation and maturation in vivo.

Emerging evidence suggests that myocyte enhancer factor 2 (MEF2) transcription factors act as effectors of neurogenesis in the brain, with MEF2C the predominant isoform in developing cerebrocortex. Here, we show that conditional knockout of Mef2c in nestin-expressing neural stem/progenitor cells (NSCs) impaired neuronal differentiation in vivo, resulting in aberrant compaction and smaller somal size. NSC proliferation and survival were not affected. Conditional null mice surviving to adulthood manifested more immature electrophysiological network properties and severe behavioral deficits reminiscent of Rett syndrome, an autism-related disorder. Our data support a crucial role for MEF2C in programming early neuronal differentiation and proper distribution within the layers of the neocortex.

Myocyte enhancer factor 2C as a neurogenic and antiapoptotic transcription factor in murine embryonic stem cells.

Cell-based therapies require a reliable source of cells that can be easily grown, undergo directed differentiation, and remain viable after transplantation. Here, we generated stably transformed murine ES (embryonic stem) cells that express a constitutively active form of myocyte enhancer factor 2C (MEF2CA). MEF2C has been implicated as a calcium-dependent transcription factor that enhances survival and affects synapse formation of neurons as well as differentiation of cardiomyocytes. We now report that expression of MEF2CA, both in vitro and in vivo, under regulation of the nestin enhancer effectively produces "neuronal" progenitor cells that differentiate into a virtually pure population of neurons. Histological, electrophysiological, and behavioral analyses demonstrate that MEF2C-directed neuronal progenitor cells transplanted into a mouse model of cerebral ischemia can successfully differentiate into functioning neurons and ameliorate stroke-induced behavioral deficits.

The impact of neurotechnology on rehabilitation.

This paper present results of a multi-disciplinary project that is developing a microchip-based neural prosthesis for the hippocampus, a region of the brain responsible for the formation of long-term memories. Damage to the hippocampus is frequently associated with epilepsy, stroke, and dementia (Alzheimer's disease) and is considered to underlie the memory deficits related to these neurological conditions. The essential goals of the multi-laboratory effort include: (1) experimental study of neuron and neural network function--how does the hippocampus encode information? (2) formulation of biologically realistic models of neural system dynamics--can that encoding process be described mathematically to realize a predictive model of how the hippocampus responds to any event? (3) microchip implementation of neural system models--can the mathematical model be realized as a set of electronic circuits to achieve parallel processing, rapid computational speed, and miniaturization? and (4) creation of hybrid neuron-silicon interfaces-can structural and functional connections between electronic devices and neural tissue be achieved for long-term, bi-directional communication with the brain? By integrating solutions to these component problems, we are realizing a microchip-based model of hippocampal nonlinear dynamics that can perform the same function as part of the hippocampus. Through bi-directional communication with other neural tissue that normally provides the inputs and outputs to/from a damaged hippocampal area, the biomimetic model could serve as a neural prosthesis. A proof-of-concept will be presented in which the CA3 region of the hippocampal slice is surgically removed and is replaced by a microchip model of CA3 nonlinear dynamics--the "hybrid" hippocampal circuit displays normal physiological properties. How the work in brain slices is being extended to behaving animals also will be described.

Neuronal network morphology and electrophysiologyof hippocampal neurons cultured on surface-treated multielectrode arrays.

Toward the development of biocompatible surfaces for implantable electrode arrays and the creation of patterned neuronal networks, the impact of select biochemical substrates [poly-D-lysine (PDL), polyornithine (PO), polyethylenimine (PEI), and a basement membrane extract (BM)] on network morphology and spontaneous electrophysiological activity of dissociated hippocampal neurons was investigated. Cultured in serum-free Neurobasal medium at 100 000 cells/cm(2), neurons attached to each substrate. PDL, PO, and PEI induced little or no neuronal clustering and process fasciculation, whereas the addition of BM promoted these features. The ratios of somas to processes, and axons to dendrites, as determined by immunohistochemical staining and image analysis were comparable across all substrates. Spontaneous firing was recorded using planar multielectrode arrays (MEAs) at the third week in vitro for the two most divergent morphologies according to Euclidian cluster analysis, namely those induced by PO + BM and PEI. Mean spike amplitude, mean firing rate, median interspike interval (ISI), mean burst rate, and correlation index were analyzed and compared to morphological features. Synchronized bursting was highly correlated with neuronal clustering and process fasciculation. Spike amplitude was negatively correlated with thin branching which was most evident in neurons grown on PEI. These data indicate that factors, which influence adherence of neurons to surfaces, can profoundly impact both neuronal network morphology and electrophysiological activity in vitro.

Receptor-ligand-based specific cell adhesion on solid surfaces: hippocampal neuronal cells on bilinker functionalized glass.

Cell adhesion through binding between specific cell membrane receptors and corresponding cell-adhesion-molecule (CAM)-coated solid surfaces is examined. The morphology of surfaces at various modification steps leading to functionalization with cell-binding CAMs is characterized. In one week neuron cultures, enhanced growth on surfaces modified with neuron-binding versus astrocyte-binding CAMs is observed. However, nonspecific adhesion on a poly-D-lysine-coated positive control surface is found to be even higher. Potential reasons and further studies needed are discussed.

Custom-designed high-density conformal planar multielectrode arrays for brain slice electrophysiology.

Multielectrode arrays have enabled electrophysiological experiments exploring spatio-temporal dynamics previously unattainable with single electrode recordings. The finite number of electrodes in planar MEAs (pMEAs), however, imposes a trade-off between the spatial resolution and the recording area. This limitation was circumvented in this paper through the custom design of experiment-specific tissue-conformal high-density pMEAs (cMEAs). Four configurations were presented as examples of cMEAs designed for specific stimulation and recording experiments in acute hippocampal slices. These cMEAs conformed in designs to the slice cytoarchitecture whereas their high-density provided high spatial resolution for selective stimulation of afferent pathways and current source density (CSD) analysis. The cMEAs have 50 or 60 microm center-to-center inter-electrode distances and were manufactured on glass substrates by photolithographically defining ITO leads, insulating them with silicon nitride and SU-8 2000 epoxy-based photoresist and coating the etched electrode tips with gold or platinum. The ability of these cMEAs to stimulate and record electrophysiological activity was demonstrated by recording monosynaptic, disynaptic, and trisynaptic field potentials. The conformal designs also facilitated the selection of the optimal electrode locations for stimulation of specific afferent pathways (Schaffer collaterals; medial versus lateral perforant path) and recording the corresponding responses. In addition, the high-density of the arrays enabled CSD analysis of laminar profiles obtained through sequential stimulation along the CA1 pyramidal tree.