Analysis and microelectronic design of tubular electrode arrays intended for chronic,multiple singleunit recording from captured nerve fibres

The paper discusses proposals for recording multiple single-unit potentials from nerve fibres that become captured in an array of tube electrodes. Capturing may be through regeneration of cut fibres or by placement of dissected filaments into grooves which are then covered. The factors contributing to signal-to-noise ratios obtainable with this type of electrode are discussed. The design, construction and bench-test results are given for an electrode array in which thin-film microelectronic techniques are used to build a densely packed, flexible, 3-dimensional electrode array consisting of a bundle of plastic tubes with flat metal contacts at midtube.     

A driveable bundle of microwires for collecting single-unit data from freely-moving rats

A technique is described for making a sturdy, driveable electrode array of ten fine wires. This moveable array is a modification of a stationary electrode [4]. It has a number of notable advantages over other electrodes designed for recording single-unit activity in freely-moving small mammals. With this electrode many single cells can be recorded in each animal, cells can be held for many days, and recording quality is very good.     

Laser-drilled multichannel multidepth extracellular microelectrodes

The paper describes the construction and characteristics of a new multichannel, multidepth microelectrode designed for extracellular biopotential recording. The electrode is constructed from a group of six borosilicate glass capillary tubes which are hot drawn to form 40–50 μm tubes. A CO₂ laser of 400 kW cm⁻² peak power is used to cut side holes in the drawn tubes of 30–40 μm diameter and at intervals of 200 μm in respective tubes, thus creating six electrodes at six different depths. When filled with 9·9M NaCl solution typical electrode resistance is 300 kΩ and the interelectrode resistance 800 kΩ. Delay in publication due to temporary withdrawal of paper during patent application     

A rigid setup for microelectrode research in fish

The setup for microelectrode recording in fish includes: (a) a head-holding set of lateral pressor feet mounted on advancing screws, and a rigid mouth tube. The mouth tube is connected to a recirculation system which enables pumping aerated water into the fish's buccopharynx. The head-holding devices are mounted on (b) a plastic box, which contains the fish and rests on (c) a heavy metal plate on which are anchored 2 steel bars. These bars run alongside the fish box and serve to support currently available stereotaxic electrode holders and micromanipulators.     

A procedure for chronic microelectrode recording from cerebellar cortex in the awake cat and monkey

A technique for chronic microelectrode recording from the cerebellar cortex in the conscious cat and monkey is presented. This technique permits recording from specific folia of the cerebellar vermis by providing direct visualization of the area.     

Design considerations in the development and application of microdisc electrode arrays (MDEAs) for implantable biosensors

The use of microlithographically fabricated Microdisc Electrode Arrays (MDEAs) in the development of implantable voltammetric biosensors necessitates design criteria that balances the overall footprint of the device with the advantages to be derived from large separation distances between non-interacting microdisc elements. Using the dynamic electroanalytical techniques of Multiple Scan Rate Cyclic Voltammetry (MSRCV) experiments with finite element simulations and Electrochemical Impedance Spectroscopy with equivalent circuit modeling, three unique MDEA designs; MDEA 050 (r = 25 μm, 5,184 discs), MDEA 100 (r = 50 μm, 1,296 discs) and MDEA 250 (r = 125 μm, 207 discs) of constant critical dimensions (center-to-center d/r = 4) and area (A = 0.1 cm²) were studied in 1.0 mM ferrocene monocarboxylic acid (FcCO₂H) solution (in 0.1 M Tris/0.1 M KCl buffer, pH = 7.2). The critical disc-to-disc spacing (d/r) required to archive 67% of maximal current response was defined as optimal. Based on the predictive model, new MDEA designs; MDEA 001 (r = 0.5 μm, 127,324 discs), MDEA 002.5 (r = 1.25 μm, 20,372 discs), MDEA 005 (r = 2.5 μm, 5,093 discs), MDEA 010 (r = 5 μm, 1,273 discs), MDEA 015 (r = 7.5 μm, 566 discs), MDEA 020 (r = 10 μm, 318 discs) were simulated at 10 and 100 mV/s. The final disc count of each MDEA was dictated by the need to maintain a comparable electroactive area between the MDEAs, which was chosen to be 0.001 cm², which in turn was dictated by the need to generate sufficient electrochemical current to be comfortably measured by common electrochemical detectors.     

Loss of place specificity in hippocampal complex spike cells of senescent rat

Firing characteristics of “place” cells in dorsal CA1 of hippocampus were recorded from 5 young (10–14 months) and 5 old (25–29 months) Fischer-344 rats. Animals were trained to obtain food reward on a radial 8-arm maze. Entry to the arms was controlled by the experimenter so that all 8-arm were visited in random sequence from trial to trial. For each cell, 8 such trials were given (64 arm choices) in order that statistical reliabilty could be obtained for firing rates over the maze surface. Single unit activity and the animal's position on the maze were continuously monitored by digital computer. Twenty-seven cells from each age group were studied in this way. No statistically significant differences were found between age groups in unit spike height, width or firing rates. A large, statistically significant difference, however, was found in both spatial specificity and reliability of firing patterns from trial to trial. These results are discussed in terms of a possible deficit in spatial information processing in the older animals.     

Self-contained dual chronic cryoprobe for deep neural structures.

This new cryoprobe-supporting system being self-contained can therefore be used for chronic animals. It enables 2 cryoprobes to be simultaneously introduced. It is movable which allows the cryoprobe positions to be modified along the 3 axes: anteroposterior, lateral or vertical.     

Microdrive and method for single unit recording in the active rat

A technique for recording single unit activity in the active rat with microelectrodes is described. The microdrive used is small and light enough to be carried in a well that is chronically implanted on the head of the rat. The device permits standard microelectrodes to be lowered without rotation, a feature which reduces chance of damage to the fine tips and to the brain tissue. The microdrive itself may be rotated in the well and several penetrations in a single preparation are possible. The electrodes used are capable of recording unit activity of high amplitude and stability. Units may be held for minutes or hours depending on the intensity of the rat's behavior.     

A low-cost,high-precision scope calibrator

A simple scope calibrator for voltage and time calibration is described. A square pulse of calibrated amplitude and pulse-width can be triggered in synchrony with CRO seeep, and displayed, with an adjustable delay, simultaneously with biological signals on CRO screen. The output of the device is isolated from ground and has a low output impedance (less than 50 for most ranges). Both the amplitude (10 V–1V) and pulse-width (0.2–1000 ms) of the outputs cover wide ranges in 1–2–5 steps with an accuracy of less than ±1%. The output drifts against changes in power supply and temperature are negligibly small. The circuit is designed to give the high performance at reasonably low cost, and to be built with only the components readily available in the market.     

Cell finder speeds impalements with microelectrodes

A simple circuit is described, which, in conjunction with an electrometer and a digitally-controlled hydraulic microdrive, automatically advances a microelectrode through the bathing solution and halts the microelectrode when a cell is impaled. The distance between initial contact with the cell membrane and cell penetration (1–5 m for rabbit corneal epithelium) is dependent upon the physical characteristics of the cell and microelectrode, and can be optimized by empirical adjustment.Supported by USPHS grant EY03311 from the National Eye Institute, Bethesda, MD, USA.     

A simple gas-flow chamber for cultured cell electrophysiology in a controlled atmosphere

A simple and inexpensive device is described to control the gaseous environment while recording membrane potentials and contractile motion from single cultured cells. This equipement was used to study the electrophysiological and mechanical responses to hypoxia of cultured rat heart cells, but should also be suitable for a wide range of applications with several cell types.     

Application of a PDMS microstencil as a replaceable insulator toward a single-use planar microelectrode array

Here we present a novel idea for a replaceable insulator, and thus advance toward the goal of a single-use planar microelectrode array (MEA) for the study of electrogenic tissues. The concept of a replaceable insulator is motivated by insulator degradation after repeated usage of an MEA. Instead of fabricating a more durable insulator for repeated MEA usage, we propose replacing the insulator and effectively producing a fresh MEA for each experiment. We chose a polydimethylsiloxane (PDMS) microstencil as a candidate for the replaceable insulator as it is biocompatible, shows reversible adhesion to surfaces, and can be easily and controllably fabricated. As a proof-of-concept, we demonstrate two applications using microstencils: the rejuvenation of an old MEA and the fabrication of a single-use MEA. These MEAs were tested with dissociated neural cell cultures and neural recordings were performed at 14 days in vitro. Inexpensive and quick supply of insulators with micrometer-sized holes provides a way of constructing an MEA that can be treated as a disposable component in high throughput cell-based biosensor applications.     

A quasi-totally shielded,low-capacitance glass-microelectrode with suitable amplifiers for high-frequency intracellular potential and impedance measurements

The fabrication of a new glass microelectrode for high-speed recording is reported. It consists of a Ling-Gerard microelectrode which is slit into a spacer capillary with the tip slightly protruding. Except for the ultimate tip (of 30 m length) the entire assembly is coated with silver and insulated. After proper insertion into the cell the electrode provides a shield, which extends from the surface of the cell membrane up to the input of the amplifier. This electrode has two advantages: 1. it eliminates all capacitive pickup of bath potentials which is of paramount importance in impedance measurements and 2. if used in conjunction with negative capacitance amplifiers, it allows more faithful high-frequency recordings, than was possible with the conventional techniques, because the capacitance neutralization can be properly set even though the non-ideal transmission properties of the electrode tips are not known. Test experiments using a rapid amplifier circuit of own design show that the electrode assembly allows error-free phaseshift measurements of up to 30 kHz to be obtained with electrodes of 20 M or risetimes (10–90%) of squarewave pulses of 10 to 12 s. The corresponding time constants of 5 to 6 s indicate that the time resolution of the new technique is superior to the apparent time resolution of the conventional techniques.     

Laminar distribution of preferred orientations in foveal striate cortex of the monkey

Summary Microelectrode penetrations normal to the layers of foveal striate cortex in awake, behaving monkeys have revealed two new facts about the distribution of orientation preferences in this tissue: (1) In the top layers there is a predominance of vertical orientation preferences at eccentricities of less than 30 min, and a predominance of oblique orientation preferences at eccentricities of 30 min to 2 deg. (2) At all eccentricities between 0 and 2 deg there is a striking difference in orientation preference between upper layer (supragranular) and lower layer (infragranular) cells.Supported by NIH grants EY02349 and 5 T32 EYO 7019     

I. Functional properties of neurons in lateral part of associative area 7 in awake monkeys

Summary The lateral part of area 7, area 7b, of alert, behaving macaque monkeys was investigated using transdural microelectrode recording technique. Two hundred twenty-eight cells from five hemispheres of four monkeys were isolated and studied. The functional properties of 2% of the cells isolated remained unidentified. Functions of the identified cells were prominently related to the spatial control of arm movements.Of the cells 70% responded to somatosensory (40%) or visual (16%) or both somatosensory and visual (14%) stimulation. The receptive fields of these passively drivable cells were large, covering, e.g., the arm or leg or chest or even the skin of the whole body. Most of the visually drivable cells responded to stimuli in both halves of the visual field.Of the cells responding to sensory stimulation 80% were activated by stimuli moving in a certain direction. Of the directionally selective cells 25% received information through more than one sensory channel. The complex stimulus-response relationships of these convergence cells revealed the existence of an integrative system which analyzes the direction of a stimulus moving in one sensory system using an other sensory system as a reference.Of all the cells isolated 28% discharged only during active movements of the arms (25%) or eyes (3%). Firing of these neurons was related to contraction of a functionally uniform group of muscles and not individual muscles.Some previous investigations of the parietal association cortex, conducted mainly in area 7a, have shown that most cells are active only when the monkey himself moves his eyes or arms. In our study on area 7b most cells responded to passive stimulation. The discrepancy between the results indicates functional differentiation within area 7.     

II. Functional properties of cells in anterolateral part of area 7 associative face area of awake monkeys

Summary The most anterior part of area 7 of awake, behaving macaque monkeys was investigated using single cell recording technique. Eighty-five cells from three hemispheres of two monkeys were isolated and studied. These cells showed more complex functional properties than the cells in the primary and secondary cortical fields. Of the cells 61% responded to somatosensory (26%) or visual (2%) or both somatosensory and visual (33%) stimulation; 39% of the cells were active only during the monkey's own movements.Most of the cells studied were active while the monkey was bringing an object to the mouth with its hand, when reaching for an object with lips, or while chewing. The neurons responded selectively to, e.g., palpation of the flexors of the arm, a visual stimulus approaching the face, passive movement of the monkey's hand towards the mouth, or they were active only when the monkey was reaching for an object with its lips or was mouthing it.The cellular activity in the anterolateral part of area 7 was prominently related to the stimulation or motor activity of the face (especially the mouth). In this respect, it differed from the more posterior part of area 7 adjacent to it. The results thus indicate that there is a separate and rather extensive mouth (or face) area in the parietal association cortex of the monkey.     

A method for simultaneously recording neural activity and rotation in the rat

An apparatus is described which allows the simultaneous recording of neural activity and rotational behaviour in the rat. Rotational behaviour is measured, coded and stored on magnetic tape along with neural activity from chronically implanted electrodes, allowing off-line computer analysis.     

Functional properties of neurons in the temporo-parietal association cortex of awake monkey

Summary The temporo-parietal association cortex around the caudal end of the Sylvian fissure was studied with the single cell recording technique in three awake behaving Macaca speciosa-monkeys. Of the 197 cells isolated, 5% were active only during the monkey's own movements, mostly during head rotation, and 95% were responsive to sensory stimulation: 54% to auditory stimuli, 24% to somatosensory stimuli, 13% to both of these and 4% to visual stimuli. Some cells, classified as responsive to somatosensory stimuli, were activated only by passive rotation of the head on the cervical axis; it is possible that they were driven by vestibular stimuli. Half of the cells were activated by stimuli on both sides of the monkey, and almost all the rest, only by stimuli on the side contralateral to the hemisphere recorded.Of the acoustically drivable cells, 95% responded to natural sounds, such as, rubbing hands together, rustle of clothes, clicks or jingles (sounds with noise spectrum and rapid intensity transitions). Most of these neurons were also examined with pure tones of 0.2–20 kHz: various inhibitory or excitatory responses were elicited in half of them, usually over a wide range of frequencies. The responses of most acoustically drivable cells (62%) depended on the location of the sound source with reference to the monkey's head so that the maximal response was elicited by sounds with a certain angle of incidence, usually on the contralateral side.The present results suggest that the area studied participates in the analysis of the temporal pattern of a sound, the location of the sound source and in spatial control of head movements.