A miniature three-channel preamplifier for unit recording in freely moving animals

A miniature, three-channel high input and low output impedance preamplifier is described for extracellular unit recording in freely moving animals. A MOSFET and an integrated circuit operational amplifier provide the two stages of each of the three amplifiers. The overall gain is approximately 200, down 6db at 1.5 Hz and 5 kHz. The peak-to-peak broadband noise amplitude with a source resistance of 10 kΩ is 10μV.     

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.     

Three-dimensional hall effect accelerometer for recording head movements of freely moving laboratory animals

A Hall effect device was constructed for a measurement of head movements in three spatial dimensions during classical conditioning experiments in cats. A Hall sensor was used to detect movements of a magnetic fragment floating in a small (15 x 15 mm) cube. The magnetic fragment was kept in the centre of the sealed cube with a thin coil spring which was filled with thin oil for damping excessive afteroscillations. A comparison of this device to a commercial accelerometer showed that the accuracy of the Hall device is sufficient for the movement recordings and that the device is sensitive also to slowly accelerating movements. The construction is compact and can be easily mounted, for example, on the head stage of a freely moving animal.     

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.     

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.     

An intra-cerebral drug delivery system for freely moving animals

Microinfusions of drugs directly into the central nervous system of awake animals represent a widely used means of unravelling brain functions related to behaviour. However, current approaches generally use tethered liquid infusion systems and a syringe pump to deliver drugs into the brain, which often interfere with behaviour. We address this shortfall with a miniaturised electronically-controlled drug delivery system (20?×?17.5?×?5?mm(3)) designed to be skull-mounted in rats. The device features a micropump connected to two 8-mm-long silicon microprobes with a cross section of 250?×?250?μm(2) and integrated fluid microchannels. Using an external electronic control unit, the device allows infusion of 16 metered doses (0.25?μL each, 8 per silicon shaft). Each dosage requires 3.375 Ws of electrical power making the device additionally compatible with state-of-the-art wireless headstages. A dosage precision of 0.25?±?0.01?μL was determined in vitro before in vivo tests were carried out in awake rats. No passive leakage from the loaded devices into the brain could be detected using methylene blue dye. Finally, the device was used to investigate the effects of the NMDA-receptor antagonist 3-((R)-2-Carboxypiperazin-4-yl)-propyl-1-phosphonic acid, (R)-CPP, administered directly into the prefrontal cortex of rats during performance on a task to assess visual attention and impulsivity. In agreement with previous findings using conventional tethered infusion systems, acute (R)-CPP administration produced a marked increase in impulsivity.     

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.     

Head mount for the control of infusion in freely moving animals.

The construction of a light weight head mount for the control of infusion in small laboratory animals is described. The head mount reduces restraint of the animal and includes a valve to seal the cannula so that the animal may be disconnected from the infusion system.     

Laser speckle contrast imaging of cerebral blood flow in freely moving animals

We designed a miniature laser speckle imager that weighs ～20 g and is 3.1-cm high for full-field high-resolution imaging of cerebral blood flow (CBF) in freely moving animals. Coherent laser light illuminates the cortex through a multimode optical fiber bundle fixed onto the supporting frame of the imager. The reflected lights are then collected by a miniature macrolens system and imaged by a high-resolution CMOS camera at a high frame rate (50 fps). Using this miniature imager, we achieve high spatiotemporal resolution laser speckle contrast imaging of CBF in freely moving animals in real time.     

Diode probes for spatiotemporal optical control of multiple neurons in freely moving animals

Neuronal control with high temporal precision is possible with optogenetics, yet currently available methods do not enable to control independently multiple locations in the brains of freely moving animals. Here, we describe a diode-probe system that allows real-time and location-specific control of neuronal activity at multiple sites. Manipulation of neuronal activity in arbitrary spatiotemporal patterns is achieved by means of an optoelectronic array, manufactured by attaching multiple diode-fiber assemblies to high-density silicon probes or wire tetrodes and implanted into the brains of animals that are expressing light-responsive opsins. Each diode can be controlled separately, allowing localized light stimulation of neuronal activators and silencers in any temporal configuration and concurrent recording of the stimulated neurons. Because the only connections to the animals are via a highly flexible wire cable, unimpeded behavior is allowed for circuit monitoring and multisite perturbations in the intact brain. The capacity of the system to generate unique neural activity patterns facilitates multisite manipulation of neural circuits in a closed-loop manner and opens the door to addressing novel questions.     

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.