Optimal signal filtering parameters for tetrode recording of neuronal activity

Extracellular recording of neuronal spiking is the main method of investigation of involvement of neurons in behavioral tasks. Development of multichannel electrodes made it possible to simultaneously record activity of the same group of neurons from different locations in the brain tissue. That method allows the researches to distinguish spiking of simultaneously recorded neurons by individual set of projection coefficients of amplitude parameters on axes corresponding to different channels of the multichannel electrode. We tested the possibility of effective separation of single unit spiking streams from multiunit activity recorded by tetrode and subjected to different filtering. We described the main limitations for effective spike identification and determined the optimal band of signal filtering for tetrode recording.     

An on-line realtime cardiotachograph]

A realtime cardiotachogram was devised to detect fluctuation of cardiac rhythm. The apparatus is composed of five parts; (1) a "preamplifier" for recording electrical and/or mechanical cardiac activities, (2) a "slicer" to obtain sampling pulses from cardiac activity at a certain trigger level, (3) a "trigger pulse generator" to monitor sampling pulse, (4) an "oscillator" whose output is fed to a pulse counter, and (5) a "pulse counter" which counts the outputs of the oscillator during the gating period determined by the sampling pulses. The count numbers are converted to analog output, thus we can get sawtooth wave whose amplitude is directly proportional to the cardiac interval. The cardiac intervals between 100 ms and 5 seconds can be recorded by this tachograph.     

A simple, PC-dedicated, implanted digital PIM-radiotelemetric system. Part 2: The multichannel system.

The paper, which is a continuation of the previous one, describes a six-channel, PC-dedicated implanted telemetry system, including the schematic drawings, and explanation of all the differences between a single channel and multichannel system approach. The scheme of an additional multichannel analog output, that makes a pure analog recording possible, even without the PC connection, is also presented. Specific methods for both parallel (Centronics) and serial (RS232C) port interfacing are demonstrated and the controlling software principles are discussed. The representative recordings obtained from animal experiments of simultaneous (direct and integrated) multichannel intestinal EMG (MMC) are shown. The device can also be used for the ECG, EEG and uterine smooth muscle electrical activity recording.     

Spectral and Temporal Acoustic Features Modulate Response Irregularities within Primary Auditory Cortex Columns

Assemblies of vertically connected neurons in the cerebral cortex form information processing units (columns) that participate in the distribution and segregation of sensory signals. Despite well-accepted models of columnar architecture, functional mechanisms of inter-laminar communication remain poorly understood. Hence, the purpose of the present investigation was to examine the effects of sensory information features on columnar response properties. Using acute recording techniques, extracellular response activity was collected from the right hemisphere of eight mature cats (felis catus). Recordings were conducted with multichannel electrodes that permitted the simultaneous acquisition of neuronal activity within primary auditory cortex columns. Neuronal responses to simple (pure tones), complex (noise burst and frequency modulated sweeps), and ecologically relevant (con-specific vocalizations) acoustic signals were measured. Collectively, the present investigation demonstrates that despite consistencies in neuronal tuning (characteristic frequency), irregularities in discharge activity between neurons of individual A1 columns increase as a function of spectral (signal complexity) and temporal (duration) acoustic variations.     

A lightweight microdrive for single-unit recording in freely moving rats and pigeons

A design for an inexpensive and reliable subminiature microdrive for recording single neurons in the freely moving animal is presented. The Scribe microdrive is small and lightweight and has been used successfully to record in freely moving rats and pigeons. It would also be suitable for recording in mice. The device is simple and inexpensive yet allows for stable and precise manipulation of the recording electrodes. As a result it supports stable recordings conducted over long periods. Because the Scribe microdrive is a small-diameter device it is also suitable for multisite, multielectrode applications. Here we discuss the construction of the device and comment on its use in recording from freely moving rats and pigeons.     

Network dynamics in nociceptive pathways assessed by the neuronal avalanche model

ABSTRACT: BACKGROUND: Traditional electroencephalography provides a critical assessment of pain responses. The perception of pain, however, may involve a series of signal transmission pathways in higher cortical function. Recent studies have shown that a mathematical method, the neuronal avalanche model, may be applied to evaluate higher-order network dynamics. The neuronal avalanche is a cascade of neuronal activity, the size distribution of which can be approximated by a power law relationship manifested by the slope of a straight line (i.e., the alpha value). We investigated whether the neuronal avalanche could be a useful index for nociceptive assessment. FINDINGS: Neuronal activities were recorded with 4 X 8 multichannel electrode arrays in the primary somatosensory cortex (S1) and anterior cingulate cortex (ACC). Under light anesthesia, peripheral pinch stimulation increased the slope of the alpha value in both the ACC and S1, whereas brush stimulation increased the alpha value only in the S1. The increase in alpha values was blocked in both regions under deep anesthesia. The increase in alpha values in the ACC induced by peripheral pinch stimulation was blocked by medial thalamic lesion, but the increase in alpha values in the S1 induced by brush and pinch stimulation was not affected. CONCLUSIONS: The neuronal avalanche model shows a critical state in the cortical network for noxious-related signal processing. The alpha value may provide an index of brain network activity that distinguishes the responses to somatic stimuli from the control state. These network dynamics may be valuable for the evaluation of acute nociceptive processes and may be applied to chronic pathological pain conditions.     

Colloid-guided assembly of oriented 3D neuronal networks

A central challenge in neuroscience is to understand the formation and function of three-dimensional (3D) neuronal networks. In vitro studies have been mainly limited to measurements of small numbers of neurons connected in two dimensions. Here we demonstrate the use of colloids as moveable supports for neuronal growth, maturation, transfection and manipulation, where the colloids serve as guides for the assembly of controlled 3D, millimeter-sized neuronal networks. Process growth can be guided into layered connectivity with a density similar to what is found in vivo. The colloidal superstructures are optically transparent, enabling remote stimulation and recording of neuronal activity using layer-specific expression of light-activated channels and indicator dyes. The modular approach toward in vitro circuit construction provides a stepping stone for applications ranging from basic neuroscience to neuron-based screening of targeted drugs.     

电突触电流在单个吸气性气管运动神经元中的选择性显示

在呼吸相关神经元或其它任何类型的神经元中,与生理性自发活动相对应的电突触电流（gap junction currents,GJCs）尚未在单个神经元中被记录到,因此电突触如何参与呼吸相关的或其它类型的生理性活动,目前所知甚少。在本研究中,我们假设GJCs可在电压钳记录条件下通过消除跨膜电化学梯度在单个神经元实现选择性记录,并在单个吸气性气管迷走神经节前神经元（inspiratory tracheal preganglionic vagal motor neurons,I-TPVMs）进行验证。结果显示,用这种方法在所有I-TPVMs中均记录到GJCs,且这些神经元的GJCs可被节律性中枢吸气活动所激活。此法可用于快速探测具自发活动的神经元网络中的GJCs。     

A gradient titration apparatus for determining spectrophotometric binding isotherms.

The construction of an automatic gradient titration apparatus using a multichannel peristaltic pump and a recording spectrophotometer is described. The ability of the apparatus to faithfully generate continuous spectrophotometric binding isotherms was tested in experiments studying the interaction of DNA with neutral red. The method has been shown to require low volumes of reactants, and complete binding curves can be produced in less than 15 min. The apparatus was also used to perform automatically the method of continuous variations in experiments determining the binding stoichiometry of calmagite and magnesium ion.     

An image-free opto-mechanical system for creating virtual environments and imaging neuronal activity in freely moving Caenorhabditis elegans

Non-invasive recording in untethered animals is arguably the ultimate step in the analysis of neuronal function, but such recordings remain elusive. To address this problem, we devised a system that tracks neuron-sized fluorescent targets in real time. The system can be used to create virtual environments by optogenetic activation of sensory neurons, or to image activity in identified neurons at high magnification. By recording activity in neurons of freely moving C. elegans, we tested the long-standing hypothesis that forward and reverse locomotion are generated by distinct neuronal circuits. Surprisingly, we found motor neurons that are active during both types of locomotion, suggesting a new model of locomotion control in C. elegans. These results emphasize the importance of recording neuronal activity in freely moving animals and significantly expand the potential of imaging techniques by providing a mean to stabilize fluorescent targets.     

Structure and bioelectricity of single neurons of Helix pomatia in the intact nervous tissue during epileptic activity: Simultaneous evaluations by confocal microscopy and intracellular recordings of membrane potential changes

• 1.1. Neuronal shape during epileptic activity was studied with confocal laser scanning microscopy and intracellular recording of identified neuronal individuals in the buccal ganglia of Helixpomatia. Simultaneous observations of single Lucifer Yellow stained fibers and epileptic activity of the same neuron were done.
• 2.2. During epileptic activity, the development of several types of morphological changes were observed: local and extended swellings, constrictions, stretching of neuronal processes and release of intracellular material.
• 3.3. Morphological alterations did not only occur with epileptic activity but could also appear due to extended laser exposure of fluorescent neuronal processes.
• 4.4. Phototoxicity is discussed as a limiting factor for a valid interpretation of the morphological changes observed by confocal microscopy.

     

Strategies for minimizing 60 Hz pickup during evoked potential recording

Electrical interference at mains power supply frequency can adversely affect the recording of evoked potentials and can be especially destructive in an operating room setting. We investigated 60Hz interference in electrode cables running from subject to preamplifier and further examined methods to eliminate such interference. We conclude that braiding electrode wires is highly efficacious in such interference reduction, presumably by reducing the magnetic flux enclosed by the wires. We further indicate that the use of flexible metal hose fabricated from Permalloy 80 may effect further interference reduction.     

Validation of long-term primary neuronal cultures and network activity through the integration of reversibly bonded microbioreactors and MEA substrates

In vitro recording of neuronal electrical activity is a widely used technique to understand brain functions and to study the effect of drugs on the central nervous system. The integration of microfluidic devices with microelectrode arrays (MEAs) enables the recording of networks activity in a controlled microenvironment. In this work, an integrated microfluidic system for neuronal cultures was developed, reversibly coupling a PDMS microfluidic device with a commercial flat MEA through magnetic forces. Neurons from mouse embryos were cultured in a 100 μm channel and their activity was followed up to 18 days in vitro. The maturation of the networks and their morphological and functional characteristics were comparable with those of networks cultured in macro-environments and described in literature. In this work, we successfully demonstrated the ability of long-term culturing of primary neuronal cells in a reversible bonded microfluidic device (based on magnetism) that will be fundamental for neuropharmacological studies.     

Caspase-3 activity in the rat hippocampal slices reflects changes in synaptic plasticity

Considering the involvement of caspase-3 in neuronal plasticity, we studied caspase-3 activity in the rat hippocampal slices, and electrophysiological characteristics of extracellular responses to paired-pulse stimulation of Schaffer's collaterals in the CA1 subfield of hippocampus. Caspase-3 activity was measured after electrophysiological recording in each slice separately. Maximal caspase-3 activity was observed in the slices with low responsiveness to single afferent stimulation indicative of decreased efficacy of interneuronal interaction. This phenomenon is unrelated to depression of neuronal excitability since paired-pulse stimulation increases the synaptic efficacy to second stimulus thus restoring population spike amplitudes to normal values. In "damaged" slices with impaired spike generation up to disappearing spikes to both stimuli, caspase-3 activity was close to the normal level of the "healthy" slices. The activity of another proteinase, cathepsin B, was increased in the "damaged" slices, no correlation with the modifications of electrophysiological indices being detected. Our data suggest that high caspase-3 activity in hippocampal slices is involved in maintenance of synaptic plasticity but not necessarily related to apoptosis.     

Recording Large-scale Neuronal Ensembles with Silicon Probes in the Anesthetized Rat

Large scale electrophysiological recordings from neuronal ensembles offer the opportunity to investigate how the brain orchestrates the wide variety of behaviors from the spiking activity of its neurons. One of the most effective methods to monitor spiking activity from a large number of neurons in multiple local neuronal circuits simultaneously is by using silicon electrode arrays^1-3.Action potentials produce large transmembrane voltage changes in the vicinity of cell somata. These output signals can be measured by placing a conductor in close proximity of a neuron. If there are many active (spiking) neurons in the vicinity of the tip, the electrode records combined signal from all of them, where contribution of a single neuron is weighted by its ''electrical distance''. Silicon probes are ideal recording electrodes to monitor multiple neurons because of a large number of recording sites (+64) and a small volume. Furthermore, multiple sites can be arranged over a distance of millimeters, thus allowing for the simultaneous recordings of neuronal activity in the various cortical layers or in multiple cortical columns (Fig. 1). Importantly, the geometrically precise distribution of the recording sites also allows for the determination of the spatial relationship of the isolated single neurons⁴. Here, we describe an acute, large-scale neuronal recording from the left and right forelimb somatosensory cortex simultaneously in an anesthetized rat with silicon probes (Fig. 2).     

Image‐guided recording system for spatial and temporal mapping of neuronal activities in brain slice

In this study, we introduce the novel image‐guided recording system (IGRS) for efficient interpretation of neuronal activities in the brain slice. IGRS is designed to combine microelectrode array (MEA) and optical coherence tomography at the customized upright microscope. It allows to record multi‐site neuronal signals and image of the volumetric brain anatomy in a single body configuration. For convenient interconnection between a brain image and neuronal signals, we developed the automatic mapping protocol that enables us to project acquired neuronal signals on a brain image. To evaluate the performance of IGRS, hippocampal signals of the brain slice were monitored, and corresponding with two‐dimensional neuronal maps were successfully reconstructed. Our results indicated that IGRS and mapping protocol can provide the intuitive information regarding long‐term and multi‐sites neuronal signals. In particular, the temporal and spatial mapping capability of neuronal signals would be a very promising tool to observe and analyze the massive neuronal activity and connectivity in MEA‐based electrophysiological studies.      

Redundancy and synergy arising from pairwise correlations in neuronal ensembles

Multielectrode arrays allow recording of the activity of many single neurons, from which correlations can be calculated. The functional roles of correlations can be revealed by measures of the information conveyed by neuronal activity; a simple formula has been shown to discriminate the information transmitted by individual spikes from the positive or negative contributions due to correlations (Panzeri et al., 1999). Here, this analysis, previously applied to recordings from small ensembles, is developed further by considering a model of a large ensemble, in which correlations among the signal and noise components of neuronal firing are small in absolute value and entirely random in origin. Even such small random correlations are shown to lead to large possible synergy or redundancy, whenever the time window for extracting information from neuronal firing extends to the order of the mean interspike interval. In addition, a sample of recordings from rat barrel cortex illustrates the mean time window at which such corrections dominate when correlations are, as often in the real brain, neither random nor small. The presence of this kind of correlations for a large ensemble of cells restricts further the time of validity of the expansion.     

Action potential waveform variability limits multi-unit separation in freely behaving rats

Extracellular multi-unit recording is a widely used technique to study spontaneous and evoked neuronal activity in awake behaving animals. These recordings are done using either single-wire or multiwire electrodes such as tetrodes. In this study we have tested the ability of single-wire electrodes to discriminate activity from multiple neurons under conditions of varying noise and neuronal cell density. Using extracellular single-unit recording, coupled with iontophoresis to drive cell activity across a wide dynamic range, we studied spike waveform variability, and explored systematic differences in single-unit spike waveform within and between brain regions as well as the influence of signal-to-noise ratio (SNR) on the similarity of spike waveforms. We also modelled spike misclassification for a range of cell densities based on neuronal recordings obtained at different SNRs. Modelling predictions were confirmed by classifying spike waveforms from multiple cells with various SNRs using a leading commercial spike-sorting system. Our results show that for single-wire recordings, multiple units can only be reliably distinguished under conditions of high recording SNR (≥ 4) and low neuronal density (≈ 20,000/ mm(3)). Physiological and behavioural changes, as well as technical limitations typical of awake animal preparations, reduce the accuracy of single-channel spike classification, resulting in serious classification errors. For SNR <4, the probability of misclassifying spikes approaches 100% in many cases. Our results suggest that in studies where the SNR is low or neuronal density is high, separation of distinct units needs to be evaluated with great caution.     

PhotoMEA: an opto-electronic biosensor for monitoring in vitro neuronal network activity

PhotoMEA is a biosensor useful for the analysis of an in vitro neuronal network, fully based on optical methods. Its function is based on the stimulation of neurons with caged glutamate and the recording of neuronal activity by Voltage-Sensitive fluorescent Dyes (VSD). The main advantage is that it will be possible to stimulate even at sub-single neuron level and to record with high resolution the activity of the entire network in the culture. A large-scale view of neuronal intercommunications offers a unique opportunity for testing the ability of drugs to affect neuronal properties as well as alterations in the behaviour of the entire network. The concept and a prototype for validation is described here in detail.