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We present novel voltage stimulation buffers with controlled output current, along with recording circuits featuring adjustable high-pass cut-off filtering to perform efficient stimulation while actively suppressing stimulation artifacts in high-density microelectrode arrays. Owing to the dense packing and close proximity of the electrodes in such systems, a stimulation through one electrode can cause large electrical artifacts on neighboring electrodes that easily saturate the corresponding recording amplifiers. To suppress such artifacts, the high-pass corner frequencies of all available 2048 recording channels can be raised from several Hz to several kHz by applying a “soft-reset” or pole-shifting technique. With the implemented artifact suppression technique, the saturation time of the recording circuits, connected to electrodes in immediate vicinity to the stimulation site, could be reduced to less than 150 μs. For the stimulation buffer, we developed a circuit, which can operate in two modes: either control of only the stimulation voltage, or control of current and voltage during stimulation. The voltage-only controlled mode employs a local common-mode feedback operational transconductance amplifier with a near rail-to-rail input/output range, suitable for driving high capacitive loads. The current/voltage controlled mode is based on a positive current conveyor generating adjustable output currents, while its upper and lower output voltages are limited by two feedback loops. The current/voltage controlled circuit can generate stimulation pulses up to 30 μA with less than ±0.1% linearity error in the low-current mode, and up to 300 μA with less than ±0.2% linearity error in the high-current mode.

Biological cells are characterized by highly complex phenomena and processes that are, to a great extent, interdependent. To gain detailed insights, devices designed to study cellular phenomena need to enable tracking and manipulation of multiple cell parameters in parallel; they have to provide high signal quality and high-spatiotemporal resolution. To this end, we have developed a CMOS-based microelectrode array system for in vitro applications that integrates six measurement and stimulation functions, the largest number to date. Moreover, the system features the largest active electrode array area to date ( $4.48 \times 2.43$ mm2) to accommodate 59 760 electrodes, while its power consumption, noise characteristics, and spatial resolution (13.5- $\mu$ m electrode pitch) are comparable to the best state-of-the-art devices. The system includes: 2048 action potential (AP, bandwidth: 300 Hz–10 kHz) recording units, 32 local-field-potential (LFP, bandwidth: 1 Hz–300 Hz) recording units, 32 current recording units, 32 impedance measurement units, and 28 neurotransmitter detection units, in addition to the 16 dual-mode voltage-only or current/voltage-controlled stimulation units. The electrode array architecture is based on a switch matrix, which allows for connecting any measurement/stimulation unit to any electrode in the array and for performing different measurement/stimulation functions in parallel.

The countries of Central Asia belong mainly to Turkish speaking area, thus the Islamic religion and culture. Islam began to spread across this territory through new cultural contacts around 700 AD as a result of conquest, distant trade and missionary activities. Tendencies of Russia and Turkey towards Central Asia are increasing the danger of the conflict outbreak in the critical areas of the region. From the early 2000s until now, Central Asia has become much more divided interethnically than it was during the Soviet period. At the end of 1970s the establishment of new Islamic Movements began. The most active movements today are: Hizb Ut-Tahrir, the Islamic Movement of Uzbekistan and the Islamic Renaissance Party of Tajikistan. Extremism and radicalism are the most active, but also the smallest part of the Islamic movement in the whole world, including Central Asia. These movements have different tactics that are manifested in the form of various methods and means used for achieving objectives.

Extracellular voltage fields, produced by a neuron's action potentials, provide a widely used means for studying neuronal and neuronal-network function. The neuron's soma and dendrites are thought to drive the extracellular action potential (EAP) landscape, while the axon's contribution is usually considered less important. However, by recording voltages of single neurons in dissociated rat cortical cultures and Purkinje cells in acute mouse cerebellar slices through hundreds of densely packed electrodes, it is found, instead, that the axon initial segment dominates the measured EAP landscape, and, surprisingly, the soma only contributes to a minor extent. As expected, the recorded dominant signal has negative polarity (charge entering the cell) and initiates at the distal end. Interestingly, signals with positive polarity (charge exiting the cell) occur near some but not all dendritic branches and occur after a delay. Such basic knowledge about which neuronal compartments contribute to the extracellular voltage landscape is important for interpreting results from all electrical readout schemes. Finally, initiation of the electrical activity at the distal end of the axon initial segment (AIS) and subsequent spreading into the axon proper and backward through the proximal AIS toward the soma are confirmed. The corresponding extracellular waveforms across different neuronal compartments could be tracked.

Extracellular voltage fields produced by a neuron’s action potentials provide a primary means for studying neuron function, yet their biophysical sources remain ambiguous. The neuron’s soma and dendrites are thought to drive the extracellular action potential (EAP), while the axon is usually ignored. However, by recording voltages of single neurons in dissociated rat cortical cultures and Purkinje cells in acute mouse cerebellar slices at hundreds of sites, we find instead that the axon initial segment dominates the EAP, and, surprisingly, the soma shows little or no influence. As expected, this signal has negative polarity (charge entering the cell) and initiates at the distal end. Interestingly, signals with positive polarity (charge exiting the cell) occur near some but not all dendritic branches and occur after a delay. Such basic knowledge about which neuronal compartments contribute to the extracellular voltage field is important for interpreting results from all electrical readout schemes. Moreover, this finding shows that changes in the AIS position and function can be observed in high spatiotemporal detail by means of high-density extracellular electrophysiology.Key points summaryThe neuron’s soma and dendrites are thought to give rise to its extracellular voltage signal, while signals from the axon are usually considered negligible.Instead, we found that the largest amplitude of the extracellular signal originates from the axon initial segment, not from the soma.This finding shows that changes in the AIS position and function can be observed in high spatiotemporal detail by means of high-density extracellular electrophysiology.AbbreviationsACSFartificial cerebrospinal fluidAISaxon initial segmentAnkGankyrin-GCMOScomplementary-metal-oxide-semiconductorDMEMDulbecco’s modified eagle mediumEAPextracellular action potentialGAD67-GFPglutamic acid decarboxylase 67-green fluorescent proteinMAP2microtubule-associated protein 2.

Studies on information processing and learning properties of neuronal networks would benefit from simultaneous and parallel access to the activity of a large fraction of all neurons in such networks. Here, we present a CMOS-based device, capable of simultaneously recording the electrical activity of over a thousand cells in in vitro neuronal networks. The device provides sufficiently high spatiotemporal resolution to enable, at the same time, access to neuronal preparations on subcellular, cellular, and network level. The key feature is a rapidly reconfigurable array of 26 400 microelectrodes arranged at low pitch (17.5 μm) within a large overall sensing area (3.85 × 2.10 mm2). An arbitrary subset of the electrodes can be simultaneously connected to 1024 low-noise readout channels as well as 32 stimulation units. Each electrode or electrode subset can be used to electrically stimulate or record the signals of virtually any neuron on the array. We demonstrate the applicability and potential of this device for various different experimental paradigms: large-scale recordings from whole networks of neurons as well as investigations of axonal properties of individual neurons., Lab on a Chip, 15 (13), ISSN:1473-0197, ISSN:1473-0189

A high-density microelectrode arrays (HDMEA) with 3,150 electrodes per square millimetre was used to capture neuronal activity across various scales, including axons, dendrites, and networks. We present a new method for high-throughput segmentation of axons based on the spatial smoothness of signal delays. Comparison with both ground truth and receiver operator characteristics shows that the new segmentation method outperforms previous methods based on the signal-amplitude-to-noise ratio. Structural and functional neuronal network connectivity were reconstructed using a common extension of “Peter’s rule” and a inter-spike histogram method, respectively. Approximately one third of these connections are putative chemical synapses. We evaluated the spike patterns but did not find evidence for “polychronisation” (non-synchronous but precisely timed spike sequences). The developed framework can be used to investigate the relationship between the topology of neuronal connections and emerging temporal spike patterns observed in dissociated neuronal cultures.

We present a novel, all-electric approach to record and to precisely control the activity of tens of individual presynaptic neurons. The method allows for parallel mapping of the efficacy of multiple synapses and of the resulting dynamics of postsynaptic neurons in a cortical culture. For the measurements, we combine an extracellular high-density microelectrode array, featuring 11’000 electrodes for extracellular recording and stimulation, with intracellular patch-clamp recording. We are able to identify the contributions of individual presynaptic neurons - including inhibitory and excitatory synaptic inputs - to postsynaptic potentials, which enables us to study dendritic integration. Since the electrical stimuli can be controlled at microsecond resolution, our method enables to evoke action potentials at tens of presynaptic cells in precisely orchestrated sequences of high reliability and minimum jitter. We demonstrate the potential of this method by evoking short- and long-term synaptic plasticity through manipulation of multiple synaptic inputs to a specific neuron., Scientific Reports, 7, ISSN:2045-2322

Tethering polymers to surfaces represents the cornerstone of a wide range of applications, including the stabilization of colloids/biomolecules and the preparation of functional coatings. Unfortunately, despite the prevalence of protein-tethered polymers in the pharmaceutical sector, the analysis of such polymer monolayers on a molecular level is difficult. In this work, simple 1H NMR spectroscopy and the catalytic properties of α-chymotrypsin are used to analyze the conformational/permeability properties of protein-bound monolayers of poly(oligoethyleneglycol monomethylether methacrylate) (pOEGMA), a biocompatible comb-polymer of interest in the biomedical field. By analyzing >100 distinct conjugates of α-chymotrypsin and pOEGMA, a detailed picture of the behavior of pOEGMA on the surface of a protein was obtained. Remarkably, control of polymer conformation and inter-penetration produced a thus far overlooked molecular sieving effect. The application of this effect for the “smart” PEGylation of proteins is portrayed, from which insight is provided for the design of other therapeutic bioconjugates and functional coatings with selective permeability properties.

A novel system to cultivate and record brain slices directly on high-density microelectrode arrays (HD-MEA) was developed. This system allows to continuously record electrical activity of selected individual neurons at high spatial resolution, while monitoring neuronal network activity at the same time. For the first time, properties of single neurons and the corresponding neuronal network in an organotypic hippocampal slice culture were studied over four consecutive weeks at daily intervals., 2015 18th International Conference on Solid-State Sensors, Actuators and Microsystems (TRANSDUCERS), 2015 Transducers, ISBN:978-1-4799-8955-3, ISBN:978-1-4799-8954-6

We present a reliable and versatile microelectrode-array-device-packaging method for use in neurobiological research. The new packaging is simple, user-friendly, durable, and obviates any contamination of the sensitive electrodes (Figure 1). The packaging consists of a custom-designed injection-molded polycarbonate ring that is bonded to the surface of the CMOS chip with a specifically selected biocompatible adhesive. The utilization of capillary effects (Figure 3) in the packaging design eliminates any contamination and flooding of the sensitive electrode array by the adhesive compound or other substances. During the development phase, an automated setup was designed to measure the lifespan of the packaging; this setup was used to determine the optimal dimensions, appropriate adhesive compound and other required parameters., Procedia Engineering, 87, EUROSENSORS 2014, the 28th European Conference on Solid-State Transducers

Bursts of action potentials within neurons and throughout networks are believed to serve roles in how neurons handle and store information, both in vivo and in vitro. Accurate detection of burst occurrences and durations are therefore crucial for many studies. A number of algorithms have been proposed to do so, but a standard method has not been adopted. This is due, in part, to many algorithms requiring the adjustment of multiple ad-hoc parameters and further post-hoc criteria in order to produce satisfactory results. Here, we broadly catalog existing approaches and present a new approach requiring the selection of only a single parameter: the number of spikes N comprising the smallest burst to consider. A burst was identified if N spikes occurred in less than T ms, where the threshold T was automatically determined from observing a probability distribution of inter-spike-intervals. Performance was compared vs. different classes of detectors on data gathered from in vitro neuronal networks grown over microelectrode arrays. Our approach offered a number of useful features including: a simple implementation, no need for ad-hoc or post-hoc criteria, and precise assignment of burst boundary time points. Unlike existing approaches, detection was not biased toward larger bursts, allowing identification and analysis of a greater range of neuronal and network dynamics., Frontiers in Computational Neuroscience, 7, ISSN:1662-5188

Axons are traditionally considered stable transmission cables, but evidence of the regulation of action potential propagation demonstrates that axons may have more important roles. However, their small diameters render intracellular recordings challenging, and low-magnitude extracellular signals are difficult to detect and assign. Better experimental access to axonal function would help to advance this field. Here we report methods to electrically visualize action potential propagation and network topology in cortical neurons grown over custom arrays, which contain 11,011 microelectrodes and are fabricated using complementary metal oxide semiconductor technology. Any neuron lying on the array can be recorded at high spatio-temporal resolution, and simultaneously precisely stimulated with little artifact. We find substantial velocity differences occurring locally within single axons, suggesting that the temporal control of a neuron's output may contribute to neuronal information processing.

We present a highly configurable, high-temporal-and-spatial-resolution microelectrode array (MEA) system, fabricated in CMOS technology, featuring 26'400 platinum microelectrodes (5×9 μm 2 ) with a pitch of 17.5 μm, arranged in a rectangular grid within an overall area of 3.8×2.1 mm 2 . The array constitutes a very flexible bidirectional interface to electrogenic cells. High-throughput, subcellular-resolution recording and stimulation of large networks of neurons enable studies of information processing and learning capabilities of neurons. An exemplary recording session demonstrates the flexibility in electrode selection and shows the system's capabilities to record from widely-spaced sets of electrodes that provide a network level overview and to subsequently perform subcellular-resolution single cell recordings of selected areas of interest., The 17th International Conference on Solid-State Sensors, Actuators and Microsystems (2013 Transducers & Eurosensors XXVII), ISBN:978-1-4673-5983-2

Understanding plasticity of neural networks is a key to comprehending their development and function. A powerful technique to study neural plasticity includes recording and control of pre- and post-synaptic neural activity, e.g., by using simultaneous intracellular recording and stimulation of several neurons. Intracellular recording is, however, a demanding technique and has its limitations in that only a small number of neurons can be stimulated and recorded from at the same time. Extracellular techniques offer the possibility to simultaneously record from larger numbers of neurons with relative ease, at the expenses of increased efforts to sort out single neuronal activities from the recorded mixture, which is a time consuming and error prone step, referred to as spike sorting. In this mini-review, we describe recent technological developments in two separate fields, namely CMOS-based high-density microelectrode arrays, which also allow for extracellular stimulation of neurons, and real-time spike sorting. We argue that these techniques, when combined, will provide a powerful tool to study plasticity in neural networks consisting of several thousand neurons in vitro., Frontiers in Neural Circuits, 6, ISSN:1662-5110

To advance our understanding of the functioning of neuronal ensembles, systems are needed to enable simultaneous recording from a large number of individual neurons at high spatiotemporal resolution and good signal-to-noise ratio. Moreover, stimulation capability is highly desirable for investigating, for example, plasticity and learning processes. Here, we present a microelectrode array (MEA) system on a single CMOS die for in vitro recording and stimulation. The system incorporates 26,400 platinum electrodes, fabricated by in-house post-processing, over a large sensing area (3.85 × 2.10 mm2) with sub-cellular spatial resolution (pitch of 17.5 μm). Owing to an area and power efficient implementation, we were able to integrate 1024 readout channels on chip to record extracellular signals from a user-specified selection of electrodes. These channels feature noise values of 2.4 μVrms in the action-potential band (300 Hz-10 kHz) and 5.4 μVrms in the local-field-potential band (1 Hz-300 Hz), and provide programmable gain (up to 78 dB) to accommodate various biological preparations. Amplified and filtered signals are digitized by 10 bit parallel single-slope ADCs at 20 kSamples/s. The system also includes 32 stimulation units, which can elicit neural spikes through either current or voltage pulses. The chip consumes only 75 mW in total, which obviates the need of active cooling even for sensitive cell cultures.