Extracellular Electrical Recordings Research Articles

GRINtrode: a neural implant for simultaneous two-photon imaging and extracellular electrophysiology in freely moving animals.

In vivo imaging and electrophysiology are powerful tools to explore neuronal function that each offer unique complementary information with advantages and limitations. Capturing both data types from the same neural population in the freely moving animal would allow researchers to take advantage of the capabilities of both modalities and further understand how they relate to each other. Here, we present a head-mounted neural implant suitable for in vivo two-photon imaging of neuronal activity with simultaneous extracellular electrical recording in head-fixed or fiber-coupled freely moving animals. A gradient refractive index (GRIN) lens-based head-mounted neural implant with extracellular electrical recording provided by tetrodes on the periphery of the GRIN lens was chronically implanted. The design of the neural implant allows for recording from head-fixed animals, as well as freely moving animals by coupling the imaging system to a coherent imaging fiber bundle. We demonstrate simultaneous two-photon imaging of GCaMP and extracellular electrophysiology of neural activity in awake head-fixed and freely moving mice. Using the collected information, we perform correlation analysis to reveal positive correlation between optical and local field potential recordings. Simultaneously recording neural activity using both optical and electrical methods provides complementary information from each modality. Designs that can provide such bi-modal recording in freely moving animals allow for the investigation of neural activity underlying a broader range of behavioral paradigms.

A comparison of probe geometries for neuronal localization.

Extracellular electrical recordings capture the spiking activity of multiple neurons in the vicinity of a probe. Typically, the features of interest in these recordings are action potentials and their timing. However, for planar probes that span tens or hundreds of neurons, it is possible to identify relative spatial locations of neurons. Such spatial information may be useful for reconstructing local network structure or for improving the quality of spike sorting. We propose a Bayesian modification of a dipole-based method for estimating neural positions from waveforms recorded on multi contact probes and investigate how sensitive it is to prior knowledge about the equivalent dipole sizes of neurons and the geometry of the recording probe. In addition, we determine the probe spacing and number of contacts which produce optimal localization accuracy within the class of planar, circularly symmetric contact configurations.

Spontaneous rapid leaf movements and action potentials in Mimosa pudica L.

Movements and action potentials of Mimosa pudica L. plants, commonly known for their sensitivity to touch, were measured using time-lapse photography and extracellular electrical potential recording methods in 4-day experiments. In intact plants, spontaneous rapid leaf movements (RLMs) were revealed. The rapid downward movement of the leaf lasted approx. 1 s and the return to the previous position took approx. 17 min. Additionally, spontaneous action potentials (SAPs) with amplitudes of 3-100 mV and half-time of approx. 15 s were observed for the first time in M. pudica. Spontaneous APs propagated basipetally or acropetally with a velocity of 3-75 cm min-1 . 36% of SAPs passing along the shoots were accompanied by RLMs. There was a delay between the appearance of SAP and RLM, indicating that SAPs may trigger the RLMs.

SPARC: Modelling a Bidirectional Bioelectric Pelvic Nerve Interface

BackgroundMicturition (urination) and continence are controlled by the autonomic nervous system; disruptions to urinary control due to disease or injury significantly impair patients’ quality‐of‐life. The pelvic nerves (in human, the pelvic splanchnic nerves) provide the primary source of autonomic sensory and motor innervation to the bladder and are prime targets for electrical stimulation to treat over‐ or under‐active bladder. The pelvic nerves in both human and rat are fasciculated, but differ from other well‐studied nerves such as the vagus or sciatic nerves in largely lacking a resistive epineurium. The pelvic nerves also comprise a much higher proportion of smaller‐caliber axons than are currently implemented in existing myelinated axon models.ObjectiveTo determine the significance of the macro‐ and micro‐anatomical properties of the pelvic nerve on the stimulation and recording performance of bioelectric neural interfaces.MethodsThe functional composition of the different fascicles of the pelvic nerve were determined using a combination of immunolabeling and tract tracing from the specific regions of the lower urinary tract or large intestine in male rats. Using this data, a model of the pelvic nerves and electrode array was implemented in SIM4LIFE (zmt.swiss) and EIDORS (eidors.org) to simulate electrical stimulation and recording, respectively. Established models for myelinated and unmyelinated axons were adapted to the small‐diameter axons found in the pelvic nerve and implemented in NEURON (neuron.yale.edu), and parameter sensitivity was established using Sobel’ sensitivity analysis for different fascicle arrangements and orientations.ResultsThe pelvic nerve consists of mixed sensory and motor fascicles, with sensory projections to lower urinary or intestinal tracts projecting in distinct fascicles. Sensitivity profiles to extracellular stimulation depend on the size and orientation of the fascicles, as well as their axon type and diameter. Within‐fascicle selectivity is enhanced in the largest fascicles of the pelvic nerve, and overall thresholds are reduced in the smallest fascicles. The stimulus thresholds and conduction velocities of the small myelinated axons depend on the ultrastructural geometry of the nodal and internodal regions, with less dependence on the juxtanode, in an axon‐type‐dependent manner. Extracellular recording sensitivity profiles for clinically realistic electrodes were computed in EIDORS and validated in SIM4LIFE for predicting spontaneous and electrically evoked activity recordings. Extracellular recording sensitivity and stimulus thresholds were both most closely correlated with axon‐electrode distance.ConclusionThe macroscopic and microscopic structure of the pelvic nerve alters its sensitivity to electrical stimulation, as well as the selectivity of extracellular electrical recording. EIDORS can be used to accurately simulate extracellular recording in complex, heterogenous neural geometries.Support or Funding InformationNIH SPARC 3OT2OD023872‐01S4

Bioelectronic Recordings of Cardiomyocytes with Accumulation Mode Electrolyte Gated Organic Field Effect Transistors

Organic electronic materials offer an untapped potential for novel tools for low-invasive electrophysiological recording and stimulation devices. Such materials combine semiconducting properties with tailored surface chemistry, elastic mechanical properties and chemical stability in water. In this work, we investigate solution processed Electrolyte Gated Organic Field Effect Transistors (EGOFETs) based on a small molecule semiconductor. We demonstrate that EGOFETs based on a blend of soluble organic semiconductor 2,8-Difluoro-5,11-bis(triethylsilylethynyl)anthradithiophene (diF-TES-ADT) combined with an insulating polymer show excellent sensitivity and long-term recording under electrophysiological applications. Our devices can stably record the extracellular potential of human pluripotent stem cell derived cardiomyocyte cells (hPSCs-CMs) for several weeks. In addition, cytotoxicity tests of pharmaceutical drugs, such as Norepinephrine and Verapamil was achieved with excellent sensitivity. This work demonstrates that organic transistors based on organic blends are excellent bioelectronics transducer for extracellular electrical recording of excitable cells and tissues thus providing a valid alternative to electrochemical transistors.

Correntropy based Robust Decomposition of Neuromodulations.

Neuromodulations as observed in the extracellular electrical potential recordings obtained from Electroencephalograms (EEG) manifest as organized, transient patterns that differ statistically from their featureless noisy background. Leveraging on this statistical dissimilarity, we propose a non-iterative robust classification algorithm to isolate, in time, these neuromodulations from the temporally disorganized but structured background activity while simultaneously incorporating temporal sparsity of the events. Specifically, we exploit the ability of correntropy to asses higher - order moments as well as imply the degree of similarity between two random variables in the joint space regulated by the kernel bandwidth. We test our algorithm on DREAMS Sleep Spindle Database and further elaborate on the hyperparameters introduced. Finally, we compare the performance of the algorithm with two algorithms designed on similar ideas; one of which is a quick, simple norm based technique while the other parallels the state-of-the-art Robust Principal Component Analysis (RPCA) to achieve classification. The algorithm is able to match the performance of the state-of-the-art techniques while saving tremendously on computation time and complexity.

High-density extracellular probes reveal dendritic backpropagation and facilitate neuron classification.

Different neuron types serve distinct roles in neural processing. Extracellular electrical recordings are extensively used to study brain function but are typically blind to cell identity. Morphoelectrical properties of neurons measured on spatially dense electrode arrays have the potential to distinguish neuron types. We used high-density silicon probes to record from cortical and subcortical regions of the mouse brain. Extracellular waveforms of each neuron were detected across many channels and showed distinct spatiotemporal profiles among brain regions. Classification of neurons by brain region was improved with multichannel compared with single-channel waveforms. In visual cortex, unsupervised clustering identified the canonical regular-spiking (RS) and fast-spiking (FS) classes but also indicated a subclass of RS units with unidirectional backpropagating action potentials (BAPs). Moreover, BAPs were observed in many hippocampal RS cells. Overall, waveform analysis of spikes from high-density probes aids neuron identification and can reveal dendritic backpropagation. NEW & NOTEWORTHY It is challenging to identify neuron types with extracellular electrophysiology in vivo. We show that spatiotemporal action potentials measured on high-density electrode arrays can capture cell type-specific morphoelectrical properties, allowing classification of neurons across brain structures and within the cortex. Moreover, backpropagating action potentials are reliably detected in vivo from subpopulations of cortical and hippocampal neurons. Together, these results enhance the utility of dense extracellular electrophysiology for cell-type interrogation of brain network function.

Scaling Spike Detection and Sorting for Next-Generation Electrophysiology.

Reliable spike detection and sorting, the process of assigning each detected spike to its originating neuron, are essential steps in the analysis of extracellular electrical recordings from neurons. The volume and complexity of the data from recently developed large-scale, high-density microelectrode arrays and probes, which allow recording from thousands of channels simultaneously, substantially complicate this task conceptually and computationally. This chapter provides a summary and discussion of recently developed methods to tackle these challenges and discusses the important aspect of algorithm validation, and assessment of detection and sorting quality.

Local transmural action potential gradients are absent in the isolated, intact dog heart but present in the corresponding coronary-perfused wedge.

The left ventricular (LV) coronary‐perfused canine wedge preparation is a model commonly used for studying cardiac repolarization. In wedge studies, transmembrane potentials typically are recorded; whereas, extracellular electrical recordings are commonly used in intact hearts. We compared electrically measured activation recovery interval (ARI) patterns in the intact heart with those recorded at the same location in the LV wedge preparation. We also compared electrically recorded and optically obtained ARIs in the LV wedge preparation. Five Langendorff‐perfused canine hearts were paced from the right atrium. Local activation and repolarization times were measured with eight transmural needle electrodes. Subsequently, left ventricular coronary‐perfused wedge preparations were prepared from these hearts while the electrodes remained in place. Three electrodes remained at identical positions as in the intact heart. Both electrograms and optical action potentials were recorded (pacing cycle length 400–4000 msec) and activation and repolarization patterns were analyzed. ARIs found in the subepicardium were shorter than in the subendocardium in the LV wedge preparation but not in the intact heart. The transmural ARI gradient recorded at the cut surface of the wedge was not different from that recorded internally. ARIs recorded internally and at the cut surface in the LV wedge preparation, both correlated with optically recorded action potentials. ARI and RT gradients in the LV wedge preparation differed from those in the intact canine heart, implying that those observations in human LV wedge preparations also should be extrapolated to the intact human heart with caution.

Extracellular gastrointestinal electrical recordings: movement not electrophysiology.

Extracellular gastrointestinal electrical recordings: movement not electrophysiology.

The powerful advantages of extracellular electrical recording.

The powerful advantages of extracellular electrical recording.

Patterned photostimulation via visible-wavelength photonic probes for deep brain optogenetics.

.Optogenetic methods developed over the past decade enable unprecedented optical activation and silencing of specific neuronal cell types. However, light scattering in neural tissue precludes illuminating areas deep within the brain via free-space optics; this has impeded employing optogenetics universally. Here, we report an approach surmounting this significant limitation. We realize implantable, ultranarrow, silicon-based photonic probes enabling the delivery of complex illumination patterns deep within brain tissue. Our approach combines methods from integrated nanophotonics and microelectromechanical systems, to yield photonic probes that are robust, scalable, and readily producible en masse. Their minute cross sections minimize tissue displacement upon probe implantation. We functionally validate one probe design in vivo with mice expressing channelrhodopsin-2. Highly local optogenetic neural activation is demonstrated by recording the induced response—both by extracellular electrical recordings in the hippocampus and by two-photon functional imaging in the cortex of mice coexpressing GCaMP6.

Extracellular electrical recording of pH-triggered bursts in C6 glioma cell populations.

Glioma patients often suffer from epileptic seizures because of the tumor's impact on the brain physiology. Using the rat glioma cell line C6 as a model system, we performed long-term live recordings of the electrical activity of glioma populations in an ultrasensitive detection method. The transducer exploits large-area electrodes that maximize double-layer capacitance, thus increasing the sensitivity. This strategy allowed us to record glioma electrical activity. We show that although glioma cells are nonelectrogenic, they display a remarkable electrical burst activity in time. The low-frequency current noise after cell adhesion is dominated by the flow of Na+ ions through voltage-gated ion channels. However, after an incubation period of many hours, the current noise markedly increased. This electric bursting phenomenon was not associated with apoptosis because the cells were viable and proliferative during the period of increased electric activity. We detected a rapid cell culture medium acidification accompanying this event. By using specific inhibitors, we showed that the electrical bursting activity was prompted by extracellular pH changes, which enhanced Na+ ion flux through the psalmotoxin 1-sensitive acid-sensing ion channels. Our model of pH-triggered bursting was unambiguously supported by deliberate, external acidification of the cell culture medium. This unexpected, acidosis-driven electrical activity is likely to directly perturb, in vivo, the functionality of the healthy neuronal network in the vicinity of the tumor bulk and may contribute to seizures in glioma patients.

Problems with extracellular recording of electrical activity in gastrointestinal muscle

Motility patterns of the gastrointestinal tract are important for efficient processing of nutrients and waste. Peristalsis and segmentation are based on rhythmic electrical slow waves that generate the phasic contractions fundamental to gastrointestinal motility. Slow waves are generated and propagated actively by interstitial cells of Cajal (ICC), and these events conduct to smooth muscle cells to elicit excitation-contraction coupling. Extracellular electrical recording has been utilized to characterize slow-wave generation and propagation and abnormalities that might be responsible for gastrointestinal motility disorders. Electrode array recording and digital processing are being used to generate data for models of electrical propagation in normal and pathophysiological conditions. Here, we discuss techniques of extracellular recording as applied to gastrointestinal organs and how mechanical artefacts might contaminate these recordings and confound their interpretation. Without rigorous controls for movement, current interpretations of extracellular recordings might ascribe inaccurate behaviours and electrical anomalies to ICC networks and gastrointestinal muscles, bringing into question the findings and validity of models of gastrointestinal electrophysiology developed from these recordings.

Effects of Dopamine D2-Like Receptor Antagonists on Light Responses of Ganglion Cells in Wild-Type and P23H Rat Retinas.

In animal models of retinitis pigmentosa the dopaminergic system in the retina appears to be dysfunctional, which may contribute to the debilitated sight experienced by retinitis pigmentosa patients. Since dopamine D2-like receptors are known to modulate the activity of dopaminergic neurons, I examined the effects of dopamine D2-like receptor antagonists on the light responses of retinal ganglion cells (RGCs) in the P23H rat model of retinitis pigmentosa. Extracellular electrical recordings were made from RGCs in isolated transgenic P23H rat retinas and wild-type Sprague-Dawley rat retinas. Intensity-response curves to flashes of light were evaluated prior to and during bath application of a dopamine D2-like receptor antagonist. The dopamine D2/D3 receptor antagonists sulpiride and eticlopride and the D4 receptor antagonist L-745,870 increased light sensitivity of P23H rat RGCs but decreased light sensitivity in Sprague-Dawley rat RGCs. In addition, L-745,870, but not sulpiride or eticlopride, reduced the maximum peak responses of Sprague-Dawley rat RGCs. I describe for the first time ON-center RGCs in P23H rats that exhibit an abnormally long-latency (>200 ms) response to the onset of a small spot of light. Both sulpiride and eticlopride, but not L-745,870, reduced this ON response and brought out a short-latency OFF response, suggesting that these cells are in actuality OFF-center cells. Overall, the results show that the altered dopaminergic system in degenerate retinas contributes to the deteriorated light responses of RGCs.

Measuring Gastrointestinal Electrical Activity With Extracellular Electrodes: Author's Reply.

TO THE EDITOR: In our recent paper1 we found that 2 points of intracellular microelectrode recording were insufficient to describe significant disruptions in gastric motor patterns that were caused by inhibition of acetylcholinesterase. Thus, we employed video imaging and analyzed data by image processing routines developed by Dr Hennig.1 The resulting motility maps described the aberrant patterns of gastric contractions when tissue cholinesterases were inhibited in much more detail that could be achieved using electrical recording. In describing our rationale for the technology chosen, we made reference to the unsuitability of extracellular electrical recording as a means to measure changes in slow waves, because movement artifacts dominate these measurements.2 In a previous study we found that when movements are blocked, under conditions in which slow waves are unaffected, the signals recorded with extracellular metal electrodes and many have attributed to electrophysiological events (slow waves), are inhibited.2 Thus the signals monitored by extracellular electrodes are largely artifacts of movement and do not represent authentic slow wave activity. In light of these observations, which have been reproduced in mouse, dog, monkey and human gastric muscles when movement is suppressed, it is important for studies utilizing extracellular electrical recording to be accompanied by rigorous tests insuring that the electrical signals claimed to be slow waves persist after movement is stabilized. O’Grady et al3 have invested a great effort in writing letters to editors when we have commented in several papers on the unsuitability of extracellular recording for electrophysiological measurements in GI muscles. We feel compelled to comment on the artifacts of extracellular electrical recording, because this technique has been used and continues to be used for research studies and for patient evaluations, yet adequate validation of the technique has not been provided. Extracellular array electrodes might be selected as a means to record integrated signals from slow waves, smooth muscle electrical activity and muscle contractions in the absence of other recording techniques, but the steps required to “deconvolute” these signals would be extremely complex. Modeling such signals as descriptions of gastric electrophysiology seems folly. In our view a better use of time than writing letters would be to perform rigorous and convincing control experiments that demonstrate unequivocally the degree to which movements contaminate extracellular signals. Neglecting such control experiments to exclude the possibility of movement artifacts will continue to cloud their results, and it was this skepticism about the validity of extracellular recordings and our own empirical tests that caused us to avoid this technique in our recent study.1 O’Grady et al3 claim they have performed adequate controls for movement4 but the tests they performed stopped well short of providing convincing evidence that their recordings are not the result of movement artifacts. As we have detailed previously, it may not be feasible to stabilize movements of muscular tissues in vivo to the extent required to remove any suspicion of movement artifacts from extracellular recordings in GI muscles.5 We have directly measured movement artifacts in smooth muscle sheets that are similar to the waveforms of the signals O’Grady et al3 consider as “ideal” electrical recording in response to movements of less than 50 μm. Respiratory movements, circulation of blood and muscle contractions uncontrolled by dihydropyridines are all possible sources of such tiny movements in the in vivo tests they performed.4 We have suggested that the best approach to make clear association between extracellular recording and authentic slow waves is rigorous stabilization of movements in vitro, as described in the addendum of our previous paper.2 If one is determined to monitor contraction by just looking at the tissue, then relatively high power objectives would be needed to allow observations of the tiny movements that cause significant signals (ie, several 10 seconds of μVs) to be picked up by extracellular electrodes. We fully realize the time, effort and resources that O’Grady et al3 have invested in extracellular recording and modeling the data derived from these measurements, and we sincerely hope new ideas might be developed to alleviate movement artifacts or amplify the field potentials caused by slow waves to a level where they can be captured by extracellular recording. But as things stand, this technique has not been validated as a measurement of the field potentials resulting from the transmembrane currents occurring during electrical slow waves, and as such, its authenticity in describing electrophysiological events in visceral smooth muscles will continue to be questioned. If, as claimed, extracellular recording is the “gold standard” for interpretation of slow wave frequency and patterns in gastrointestinal muscles, then how about providing a rigorous assay of the gold?

Principles of high–fidelity, high–density 3–d neural recording

New probe technologies, neural amplifier systems, and data acquisition systems enable the extracellular electrical recording of ever greater numbers of neurons in the live mammalian brain. These recordings have the potential to increase our understanding of neuronal network dynamics, but much remains uncharacterized about the possibilities and limitations of extracellular techniques. We explore these possibilities and limitations in the context of spike sorting and probe design. Spike sorting is a critical analysis step for extracellular data, which attempts to separate raw electrode traces into the activity patterns of individual neurons. Given the labor associated with manual spike sorting of large datasets, the necessity for automated spike sorting method will only increase. An automated method would ideally commit no errors in spike assignment – that is, it would associate each extracted individual neuron with all the spikes fired by a single neuron, and with no spikes not fired by that same neuron. The elimination of errors would reduce the reliance on manual validation, saving large amounts of analysis time, and also reduce downstream biases in data analyses introduced by errors in spike sorting. We explore designs for multi-electrode probes and spike sorting methods that in combination allow high accuracy in spike assignment with many neurons extracted. To this end, first, we ask if an automated spike sorting method with zero spike assignment errors is possible. Second, we explore what multi-electrode probe designs produce optimal yield using this method. We have constructed a spike sorting method for the case of spatially dense high channel count extracellular recordings, first applying a well-established source separation technique called Independent Components Analysis (ICA) to continuous recordings. Second, we apply a classifier to the ICA components, keeping only putative single neuron units that are well separated from noise and other units. To test this algorithm, we simulated multielectrode probe data that encompasses many of the realistic variations and noisinesses of natural neural data, including spatial non-linearities in spike shape from individual cells. Running this algorithm against this simulated data, for a wide range of classifier parameters, we find that no spike assignment errors are committed. This result is robust to changes in neural firing rate, neural density, Gaussian noise, and increasing electrode density on the probes. However, for probes with electrode counts similar to those in commercial probes (10-50), only a handful of neurons are extracted. Exploring the space of probe designs, we find that designing probes with higher electrode density (for a fixed area) can compensate for this low yield. As the electrode density on the probe increases, the number of neurons extracted increases to some saturation. We also find that as the electrode density increases, we are able to extract neurons with spike peak magnitudes below the thresholding noise floor. Thus, the construction of very high density multielectrode arrays, coupled to the algorithm here proposed, may yield experimental approaches for recording very large numbers of neurons in the live brain, and automatically analyzing the resulting spike trains.

On-chip optical stimulation and electrical recording from cells

We present an optoelectrical device capable of in vitro optical stimulation and electrophysiological recording. The device consists of an array of micropixellated InGaN light-emitting diodes coupled to a custom-made ultrathin planar microelectrode array. Cells can be cultured directly on the chip for short- and long-term electrophysiological experiments. To show the functionality of the device, we transfected a cardiomyocyte-like cell line (HL-1) with a light-sensitive protein channelrhodopsin. We monitored action potentials of individual, spontaneously beating, HL-1 cells growing on the chip by extracellular electrical recordings. On-chip optical stimulation was demonstrated by triggering network activity in a confluent HL-1 cell culture and visualized by calcium imaging. We see the potential of our system for electrophysiological experiments with optogenetically modified cells. Optical stimulation can be performed directly on the chip without additional optical components or external light sources.

A New Concept for Pacemaker Activity in the Human Stomach (J Physiol 2011:589[Pt 24];6105-6118)

Rhee et al1 has reported a study entitled Analysis of pacemaker activity in the human stomach in the December issue of Journal of Physiology 2011. Extracellular electrical recording techniques using animal models have contributed to establish important concepts of human gastric physiology.2,3 The electrical quiescence in the gastric fundus, 3 cycles per minute (cpm) pacemaker activity in corpus and antrum, and proximal-to-distal slow wave frequency gradient tended to accept as standard concepts. However, several findings which do not concur with those classic concepts have been presented in Rhee's study. Rhee et al1 experimented using human gastric muscles obtained from patients undergoing gastric resection for gastric cancer and investigated the slow wave pacemaker activity recorded with intracellular microelectrodes, the contractions recorded by isometric force techniques and the distribution of interstitial cells of Cajal (ICC). Interestingly, different from the recent studies, slow waves were routinely recorded from gastric fundic muscles. And similar waveforms as slow waves in more distal regions were presented with couple to phasic contractions. Also gastric slow wave frequency was significantly greater than 3 cpm in all regions of the stomach. Additionally antral slow wave frequency often exceeded the highest frequency of pacemaker activity in the corpus. These observations could not be explained as chronotropic mechanisms such as muscarinic and prostaglandin receptor binding, stretch, extracelluar Ca2+ and temperature. After all, muscles from all regions through the thickness of the muscularis demonstrated intrinsic pacemaker activity, and this corresponded with the widespread distribution in ICC.

Response from Sean M. Ward and Kenton M. Sanders

Response from Sean M. Ward and Kenton M. Sanders