A Wireless Multi-Channel Recording System for Freely Behaving Mice and Rats

To understand the neural basis of behavior, it is necessary to record brain activity in freely moving animals. Advances in implantable multi-electrode array technology have enabled researchers to record the activity of neuronal ensembles from multiple brain regions. The full potential of this approach is currently limited by reliance on cable tethers, with bundles of wires connecting the implanted electrodes to the data acquisition system while impeding the natural behavior of the animal. To overcome these limitations, here we introduce a multi-channel wireless headstage system designed for small animals such as rats and mice. A variety of single unit and local field potential signals were recorded from the dorsal striatum and substantia nigra in mice and the ventral striatum and prefrontal cortex simultaneously in rats. This wireless system could be interfaced with commercially available data acquisition systems, and the signals obtained were comparable in quality to those acquired using cable tethers. On account of its small size, light weight, and rechargeable battery, this wireless headstage system is suitable for studying the neural basis of natural behavior, eliminating the need for wires, commutators, and other limitations associated with traditional tethered recording systems

In vivo validation of the electronic depth control probes.

In this article, we evaluated the electrophysiological performance of a novel, high-complexity silicon probe array. This brain-implantable probe implements a dynamically reconfigurable voltage-recording device, coordinating large numbers of electronically switchable recording sites, referred to as electronic depth control (EDC). Our results show the potential of the EDC devices to record good-quality local field potentials, and single- and multiple-unit activities in cortical regions during pharmacologically induced cortical slow wave activity in an animal model

Toward Automated Electrode Selection in the Electronic Depth Control Strategy for Multi-unit Recordings

Multi-electrode arrays contain an increasing number of electrodes. The manual selection of good quality signals among hundreds of electrodes becomes impracticable for experimental neuroscientists. This increases the need for an automated selection of electrodes containing good quality signals. To motivate the automated selection, three experimenters were asked to assign quality scores, taking one of four possible values, to recordings containing action potentials obtained from the monkey primary somatosensory cortex and the superior parietal lobule. Krippendorff’s alpha-reliability was then used to verify whether the scores, given by different experimenters, were in agreement. A Gaussian process classifier was used to automate the prediction of the signal quality using the scores of the different experimenters. Prediction accuracies of the Gaussian process classifier are about 80% when the quality scores of different experimenters are combined, through a median vote, to train the Gaussian process classifier. It was found that predictions based also on firing rate features are in closer agreement with the experimenters’ assignments than those based on the signal-to-noise ratio alone.status: publishe

Discrete cortical responses from multi-site supra-choroidal electrical stimulation in the feline retina

Exploration into electrical stimulation of the retina has thus far focussed primarily upon the development of prostheses targeted at one of two sites of intervention - the epi- and sub-retinal surfaces. These two approaches have sound, logical merit owing to their proximity to retinal neurons and their potential to deliver stimuli via the surviving retinal neural networks respectively. There is increasing evidence, however, that electric field effects, electrode engineering limitations, and electrode-tissue interactions limit the spatial resolution that once was hoped could be elicited from electrical stimulation at epi- and sub-retinal sites. An alternative approach has been proposed that places a stimulating electrode array within the supra-choroidal space - that is, between the sclera and the choroid. Here we investigate whether discrete, cortical activity patterns can be elicited via electrical stimulation of a feline retina using a custom, 14 channel, silicone rubber and Pt electrode array arranged in two hexagons comprising seven electrodes each. Cortical responses from Areas 17/18 were acquired using a silicon-based, multi-channel, penetrating probe developed at IMTEK, University of Freiburg, within the European research project NeuroProbes. Multi-unit spike activity was recorded in synchrony with the presentation of electrical stimuli. Results show that distinct cortical response patterns could be elicited from each hexagon separated by 1.8 mm (center-to-center) with a center-to-center electrode spacing within each hexagon of 0.55 mm. This lends support that higher spatial resolution may also be discerned

Approaches for drug delivery with intracortical probes

Abstract Intracortical microprobes allow the precise monitoring of electrical and chemical signaling and are widely used in neuroscience. Microelectromechanical system (MEMS) technologies have greatly enhanced the integration of multifunctional probes by facilitating the combination of multiple recording electrodes and drug delivery channels in a single probe. Depending on the neuroscientific application, various assembly strategies are required in addition to the microprobe fabrication itself. This paper summarizes recent advances in the fabrication and assembly of micromachined silicon probes for drug delivery achieved within the EU-funded research project NeuroProbes. The described fabrication process combines a two-wafer silicon bonding process with deep reactive ion etching, wafer grinding, and thin film patterning and offers a maximum in design flexibility. By applying this process, three general comb-like microprobe designs featuring up to four 8-mm-long shafts, cross sections from 150×200 to 250×250 µm², and different electrode and fluidic channel configurations are realized. Furthermore, we discuss the development and application of different probe assemblies for acute, semichronic, and chronic applications, including comb and array assemblies, floating microprobe arrays, as well as the complete drug delivery system NeuroMedicator for small animal research.status: publishe

Wireless recording of single-unit activity from the mouse dorsal striatum during rotarod running.

<p><b>A.</b> Coronal section of a mouse brain showing superimposed electrode placement targeting the dorsal striatum. This experiment used a 2 by 8, 16 channel microwire electrode array. <b>B.</b> Photo of a mouse during a rotarod task. The wireless telemetry system allows the animal to fall and rest between trials without getting wires tangled up in the testing apparatus, yet is small and light enough that it minimally interferes in the task itself. <b>C.</b> Raster plot and peri-event time histogram of a putative medium spiny projection neuron from the dorsal striatum. The start and end of each trial are marked by triangles. Notice the clear difference in firing rates between the trial state and the resting state. The histogram bin size is 4 seconds. <b>D.</b> Action potential waveform of the neuron shown in C.</p

Wireless recording of single unit activity from the rat dorsal striatum during operant conditioning.

<p><b>A.</b> Coronal sections of a rat brain showing the striatum and the placement of the microwire arrays. A 16-channel, 2×8 microwire array was used. <b>B.</b> Rat performing operant task of pressing a small protrusion in order to receive a reward. The lever measures the force that is exerted upon it, and the reward is contingent upon the duration and force of the press. Use of the wireless telemetry system for this facilitates task acquisition and prevents the rat from chewing removing the headstage and chewing the wires. <b>C.</b> Raster plot and peri-stimulus time histogram of a putative tonically active cholinergic neuron recorded from the rat striatum. Bin size for the PSTH is 20 ms. The X-axis shows time from the delivery of a food pellet reward following a successfully completed lever press. The neuron showed burst firing immediately after reward delivery. <b>D.</b> Action potential waveform of the neuron shown in C.</p