A miniature multichannel preamplifier for recording electrophysiological activity in freely moving animals

A design for a miniature preamplifier for recording electrophysiological activity in freely moving small animals is proposed. The preamplifier is relatively simple to make and use and allows differential recording of neuron activity, EEG, and evoked potentials in multiple channels. When necessary the preamplifier can easily be disassembled for repair. A thin, flexible cable and a “gentle” suspension system prevent interference with the animal's free movement. The design is light in weight and allows electrophysiological activity to be recorded in mice even while they are swimming in a Morris tank. Translated from Zhurnal Vysshei Nervnoi Deyatel'nosti imeni I. P. Pavlova, Vol. 58, No. 1, pp. 111–116, January–February, 2008.     

Eye-movement recording in freely moving animals

A new method is described for precise recording of eye movements in freely moving animals using Hall-effect devices. This inexpensive system, of small size and low weight, allows the analysis of horizontal and vertical components of saccadic eye movements, optokinetic nystagmus, slow tracking movements, eye vergence, etc., in unrestrained animals. A set of Hall-effect devices mounted in the skull is used to sense variations in the position of high-power miniature magnets fixed to the eye sclera. The output of the Hall-effect devices is amplified by operational amplifiers and collected through an analog-to-digital converter to be displayed on-line in a personal computer and stored for later analysis by specific software. Some examples of simultaneous body- and eye-movement recordings obtained in freely moving goldfish in different experimental situations are presented. This method would be useful in the recording of eye and gaze movements under natural conditions and for behavioural studies in freely moving animals.     

A method for recording single unit activity from unanesthetized chronic cats

Under general anesthesia the cat is held in a stereotaxic instrument and a screwcapped teflon cylinder is placed in a trephine hole over the area from which microelectrode recordings are to be made. Macroelectrode leads are connected to an Amphenol receptacle which is screw-fastened into a head-holding apparatus which is rigidly attached to the stereotaxoc instrument. The receptacle is dental-cemented to the skull of the cat so that when ear, eye and mouth bars are removed, the head of the animal is still rigidly held in the stereotaxic position. During unit recording, the cat is held in a restraining box and the Amphenol plug is again fastened to the head-holding device and stereotaxic frame. The teflon cylinder is uncapped and a microelectrode is stereotaxically lowered into the brain of the cat. Cats adapt to the body and head restraint and single cells have been recorded for several hours.     

A removable head-mounted microdrive for unit recording in the free-behaving rat

The microdrive described in this paper has been used for two years for chronic unit recording in the olfactory bulbs of unrestrained rats. It is a removable micromanipulator, suitable for tungsten microelectrodes, designed for stereotaxic exploration of cylindrical areas of nervous tissue 9 mm high and 1.6 mm in dia. The electrode is moved up and down without any rotation and with minimal vibration, with a degree of precision of 5 microns.     

A sweet new multiple electrode for chronic single unit recording in moving animals

A multiple electrode assembly is described. It is composed of individually-insulated fine wires for isolation of single brain units in freely behaving animals and makes possible continuous recording from the same single unit over long periods of time. Seven or more fine (25 μm dia.) individually teflon coated platinum iridium monofilaments are inserted through the lumen of a 26 gauge stainless steel hypodermic tube, cut to the desired length, and fused into a single rigid shaft by coating in melted dextrose. The electrode is entirely prefabricated and the wires are implanted simultaneously in a selected brain area. The sugar gradually dissolves and units can be recorded within 48 hr.     

Hippocampal place units in the freely moving rat: Why they fire where they fire

Summary Place units in the dorsal hippocampus of the freely-moving rat signal the animal's position in an environment (place field). In the present experiments, thirty four place units were recorded in two different environments: one, a small platform where the rat had received neither training nor reward; the other, an elevated T-maze inside a set of black curtains where the rat had been trained on a place discrimination. The places within the curtained enclosure were specified by four cues (a light, a card, a fan, and a buzzer) in addition to the food. Other cues were eliminated by rotating the maze and the four controlled cues relative to the external world from trial-to-trial.Some units had place fields in both environments while others only had a place field in one. No relationship could be seen between the place fields of units with fields in both environments.All twelve units tested extensively in the controlled enclosure had place fields related to the controlled cues. Probe experiments in which only some of the controlled cues were available showed that some of these units were being excited by one or two cues while others were influenced in a more complex way. The fields of these latter units were maintained by any two of the 4 cues and were due to inhibitory influences which suppressed the unit firing over the rest of the maze.     

A wireless multi-channel neural amplifier for freely moving animals

Conventional neural recording systems restrict behavioral experiments to a flat indoor environment compatible with the cable that tethers the subject to recording instruments. To overcome these constraints, we developed a wireless multi-channel system for recording neural signals from rats. The device takes up to 64 voltage signals from implanted electrodes, samples each at 20 kHz, time-division multiplexes them into one signal and transmits that output by radio frequency to a receiver up to 60 m away. The system introduces <4 μV of electrode-referred noise, comparable to wired recording systems, and outperforms existing rodent telemetry systems in channel count, weight and transmission range. This allows effective recording of brain signals in freely behaving animals. We report measurements of neural population activity taken outdoors and in tunnels. Neural firing in the visual cortex was relatively sparse, correlated even across large distances and was strongly influenced by locomotor activity.     

Easy construction of an improved fine wire electrode for chronic single neuron recording in freely moving animals

An easy and improved method for construction and implantation of fine wire electrodes is described. These electrodes have been found to be effective in long-term recording of single unit activity in freely behaving and ingesting animals when chronically implanted in any region of the brain in rats.     

An accelerometer for recording head movement of laboratory animals

The construction of an inexpensive light-weight accelerometer for use as a head-movement transducer with small animals in brain-recording (or brain-stimulation) experiments is described. The accelerometer can simply be taped to the existing cables, thereby furnishing a sensitive measurement of head movement.     

A system for multiple unit recording during avoidance behavior of the rabbit

This paper describes a system for recording multiple-unit activity during avoidance conditioning of the rabbit. Three major advantages of the system are emphasized. The first is rapid and reliable single-session acquisition of the avoidance response (wheel rotation). A second advantage is the freedom from movement-related artifact provided by combining the recording and behavioral methods. Finally, the techniques of implantation of electrodes maximized the number of large-amplitude unit recordings that were obtained.     

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.     

Wireless power-supplying system for implanted electronic circuits in freely moving animals

A system for supplying power to implanted electronic circuits by means of an electromagnetic field has been developed and tested in chronic experiments with monkeys (Macaca Mulatta and Macaca Fascicularis), freely moving and interacting with each other. The transferred energy is used by electronic circuits which drive a number of telemetric multi-injectors within a headmounted container. The system makes use of batteries redundant. Besides saving space within the container this technique circumvents periodic changes of batteries, which is very important in long-term experiments, where disturbance of the social behaviour under study has to be reduced as far as possible.     

Long term recording from cortical and subcortical neurons in unrestrained cats

A system for obtaining chronic unit recording from cortical and subcortical neurons in unrestrained cats is described. This system has been used and tested in a population of trained animals for several years, and possesses the following major advantages: the microelectrode may be easily changed in the event that it becomes damaged or if a longer traverse is desired; it has proved feasible to maintain stable records from the same population of cells for as long as 14 days; the electrode can be moved through the brain of the conscious animal, affording the opportunity to map a large number of different cells in the same individual. Details of the construction of reliable glass-insulated platinum-iridium microelectrodes are presented.