Miniature three-function transmitting system for single neuron recording, wireless brain stimulation and marking

Biomedical signal acquisition with streaming wireless communication for recording evoked potentials

BACKGROUND

Commercial electrophysiology systems for recording evoked potentials always connect patients to the acquisition unit via long wires. Wires guarantee timely transfer of signals for synchronization with the stimuli, but they are susceptible to electromagnetic and electrostatic interferences. Though wireless solutions are readily available (e.g. Bluetooth), they introduce high delay variability that will distort the evoked potential traces. We developed a complete wireless acquisition system with a fixed delay.

METHODS

The system supports up to 4 bipolar channels; each is amplified by 20,000× and digitized to 24 bits. The system incorporates the "driven-right-leg" circuit to lower the common noise. Data are continuously streamed using radio-frequency transmission operating at 915 MHz and then tagged with the stimulus SYNC signal at the receiver. The delay, noise level and transmission error rate were measured. Flash visual evoked potentials were recorded monocularly from both eyes of six adults with normal vision. The signals were acquired via wireless and wired transmissions simultaneously. The recording was repeated on some participants within 2 weeks.

RESULTS

The delay was constant at 20 ms. The system noise was white and Gaussian (2 microvolts RMS). The transmission error rate was about one per million packets. The VEPs recorded with wireless transmission were consistent with those with wired transmission. The VEP amplitudes and shapes showed good intra-session and inter-session reproducibility and were consistent across eyes.

CONCLUSIONS

The wireless acquisition system can reliably record visual evoked potentials. It has a constant delay of 20 ms and very low error rate.

A digital programmable telemetric system for recording extracellular action potentials

This article describes the design and preliminary evaluation of a small-sized and low energy consumption wearable wireless telemetry system for the recording of extracellular neuronal activity, with the possibility of selecting one of four channels. The system comprises four radio frequency (RF) transceivers, three microcontrollers, and a digital amplifier and filter. This constitutes an innovative distributed processing approach. Gain, cutoff frequencies, and channel selection are remotely adjusted. Digital data transmission is used for both the bioelectrical signals and the control commands. This feature offers superior immunity to external RF interference. Real-time viewing of the acquired data allows the researcher to select only relevant data for storage. Simultaneous recordings of neuronal activity from the striatum of a freely moving rat, both with the wireless device and with a wired data acquisition system, are shown.

A remotely controlled lightweight MRI compatible ultrasonic actuator for micrometer positioning of electrodes during neuroethological primate research

The precise positioning of microelectrodes is essential for a reliable electrophysiological exploration of anatomical structures in the brain of laboratory animals, e.g., non-human primates in systemic brain research. Despite recent advances in micromechanics, the majority of small, chronically head mounted devices for advancing and retracting electrodes in freely moving animals reported in the literature are manually operated. In this article, we present a newly developed lightweight microfeed, based on an ultrasonic actuator for micrometer positioning of recording microelectrodes. It has been designed for compatibility with magnetic resonance imaging to allow non-invasive visualization of chronically implanted electrodes. The actuator combines a teleoperation via infrared control to minimize manipulation of animals during neuroethological studies. Its design is believed to add substantially to the well-being of experimental animals.

Wireless multichannel biopotential recording using an integrated FM telemetry circuit

This paper reports on the design, implementation, and testing of wireless multichannel recording microsystems featuring on-chip AC amplification, DC input stabilization, time-division-multiplexing, and wireless FM reconstruction of input biopotentials with frequency contents from 0.05-6 kHz with measured I/O correlation coefficients in the range of 70-94% per channel for spike train input amplitudes of 0.2-2 mV(p-p) while dissipating only 2.2 mW from 3 V. The 4.84 mm(2) IC is fabricated using AMI 1.5 microm 2P2M CMOS process, and is successfully interfaced with a micromachined silicon probe for simultaneous multichannel wireless in vitro recording of simulated neural spikes at 98 MHz with measured I/O correlation coefficients of >80%.

Telemetric recording of neuronal activity

A telemetric system is described which allows the wireless registration of extracellular neuronal activity and vocalization-associated skull vibrations in freely moving, socially living squirrel monkeys (Saimiri sciureus). The system consists of a carrier platform with numerous guiding tubes implanted on the skull. Custom-made microdrives are mounted on the platform, allowing the exploration of two electrode tracks at the same time. Commercially available quartz-insulated platinum-tungsten microelectrodes are used. The electrodes can be moved over a distance of 8-10 mm by turning a screw on the microdrive. Vocalization-associated skull vibrations are recorded with a piezo-ceramic element. Skull vibration signal and the signals from the two microelectrodes are fed into separate transmitters having different carrier frequencies. The signals are picked up by an antenna in the animal cage and are sent to three receivers in the central laboratory. Here, the signals are transferred via an analog/digital interface to a personal computer for data analysis and to a video recorder for long-term storage. The total weight of the head mount including carrier platform, microdrive, electrodes, skull vibration sensor, three transmitters, and protection cap is 32 g. The transmitters are powered with two rechargeable lithium batteries, allowing about 8 h of continuous recording. Reliable signal transmission is obtained over a distance of about 2 m. Recording stability allows to follow the activity of specific neurons up to several hours, with no movement artefacts during locomotion.

A lightweight telemetry system for recording neuronal activity in freely behaving small animals

A miniature lightweight radio telemetric device is described which is shown to be suitable for recording neuronal activity in freely behaving animals. Its size (12 x 5 x 8 mm) and weight (1.0-1.1 g with batteries, 0.4-0.5 g without) make the device particularly suitable for recording neuronal units in small animals such as mice or zebra finches. The device combines a high impedance preamplifier, RC-filters and an FM-transmitter. Using the device we recorded action potentials in field L of freely behaving zebra finches (12-17 g) through chronically implanted tungsten electrodes. In freely behaving birds we observed frequency dependent responses of field L units to auditory stimuli for periods of up to 7 days. We investigated the effect of the device on singing and locomotor activity of the zebra finches. Singing and locomotion were significantly affected on the first day after surgery. Both anesthesia and the presence of the transmitter contributed to the observed effect. After 1 day of recovery, singing activity returned to 99.6% and perch-hopping activity to 55.3% of the baseline levels. It is concluded that the device is well suited for recording spike trains from small animals while they behave freely and naturalistically.

Miniature neurologgers for flying pigeons: multichannel EEG and action and field potentials in combination with GPS recording

To study the neurophysiology of large-scale spatial cognition, we analyzed the neuronal activity of navigating homing pigeons. This is not possible using conventional radio-telemetry suitable for short distances only. Therefore we developed a miniaturized data logger ("neurologger") that can be carried by a homing pigeon on its back, in conjunction with a micro-global position system (GPS) logger recording the spatial position of the bird. In its present state, the neurologger permits recording from up to eight single-ended or differential electrodes in a walking or flying pigeon. Inputs from eight independent channels are preamplified, band-pass filtered, and directed to an eight-channel, 10-bit analog-digital converter of the microcontroller storing data on a "Multimedia" or "Secure Digital" card. For electroencephalography (EEG), the logger permits simultaneous recordings of up to eight channels during maximally 47 h, depending on memory, while single unit activity from two channels can be stored over 9 h. The logger permits single unit separation from recorded multiunit signals. The neurologger with GPS represents a better alternative to telemetry that will eventually permit to record neuronal activity during cognitive and innate behavior of many species moving freely in their habitats but will also permit automated high-throughput screening of EEG in the laboratory.

Wireless multichannel biopotential recording using an integrated FM telemetry circuit

This paper presents a four-channel telemetric microsystem featuring on-chip alternating current amplification, direct current baseline stabilization, clock generation, time-division multiplexing, and wireless frequency-modulation transmission of microvolt- and millivolt-range input biopotentials in the very high frequency band of 94-98 MHz over a distance of approximately 0.5 m. It consists of a 4.84-mm2 integrated circuit, fabricated using a 1.5-microm double-poly double-metal n-well standard complementary metal-oxide semiconductor process, interfaced with only three off-chip components on a custom-designed printed-circuit board that measures 1.7 x 1.2 x 0.16 cm3, and weighs 1.1 g including two miniature 1.5-V batteries. We characterize the microsystem performance, operating in a truly wireless fashion in single-channel and multichannel operation modes, via extensive benchtop and in vitro tests in saline utilizing two different micromachined neural recording microelectrodes, while dissipating approximately 2.2 mW from a 3-V power supply. Moreover, we demonstrate successful wireless in vivo recording of spontaneous neural activity at 96.2 MHz from the auditory cortex of an awake marmoset monkey at several transmission distances ranging from 10 to 50 cm with signal-to-noise ratios in the range of 8.4-9.5 dB.

Miniature telemetry system for the recording of action and field potentials

A simple miniature telemetry system for neural recording from freely moving rats is described. It weighs only 1% of the body weight of an adult rat and its recordings are devoid of artifacts due to the animal movement. Together with its long recording time (more than 38 h), its isotropic nature, which is essential for working with freely moving animals, offers further advantages. A frequency-modulation receiver with a flat frequency response down to 6 Hz has been designed for wide-spectrum recording of neural signals, allowing field potential recordings. A detailed printed-circuit layout and the lack of a trimming requirement will allow the system to be easily duplicated by other neuroscientists who are not familiar with wireless-transmission technologies.

Wireless transmission of fast-scan cyclic voltammetry at a carbon-fiber microelectrode: proof of principle

Fast-scan cyclic voltammetry (FSCV) at a carbon-fiber microelectrode (CFM) provides exquisite temporal and spatial resolution for monitoring brain chemistry. The utility of this approach has recently been demonstrated by measuring sub-second dopamine changes associated with behavior. However, one drawback is the cable link between animal and recording equipment that restricts behavior and precludes monitoring in complex environments. As a first step towards developing new instrumentation to overcome this technical limitation, the goal of the present study was to establish proof of principle for the wireless transmission of FSCV at a CFM. Proof of principle was evaluated in terms of measurement stability, fidelity, and susceptibility to ambient electrical noise. Bluetooth digital telemetry provided bi-directional communication between remote and home-base units and stable, high-fidelity data transfer comparable to conventional, wired systems when tested using a dummy cell (i.e., a resistor and capacitor in series simulating electrical properties of a CFM), and dopamine measurements with flow injection analysis and in the anesthetized rat with electrical stimulation. The wireless system was also less susceptible to interference from ambient electrical noise. Taken together, the present findings establish proof of principle for the wireless transmission of FSCV at a CFM.

Miniature stereo radio transmitter for simultaneous recording of multiple single-neuron signals from behaving owls

Wireless radiotelemetric transmission of neuronal activity is an elegant technique to study brain-behavior interaction in unrestrained animals. In the current study, a miniature FM-stereo radio transmitter is described that permitted simultaneous recordings from two microelectrodes in behaving barn owls. Input from two independent channels is multiplexed to form a stereo composite signal that modulates a radio frequency carrier. The high quality of broadcasted extracellular signals enabled separation of single units based on differences in spike waveforms. Recording several single cells from different electrodes allows the possibility of investigating correlations between small, distributed neuronal ensembles. Multi-channel radiotelemetry that meets the demands of modern electrophysiology might open a new perspective for combined behavioral/neurophysiological approaches in freely-behaving animals.

Adjustable frequency selectivity of auditory forebrain neurons recorded in a freely moving songbird via radiotelemetry

One of the hearing system's basic properties that determines the detection of signals is its frequency selectivity. In the natural environment, a songbird may achieve an improved detection ability if the neuronal filters of its auditory system could be sharpened to adapt to the spectrum of the background noise. To address this issue, we studied 35 multi-unit clusters in the input layer of the primary auditory forebrain of nine European starlings (Sturnus vulgaris). Microelectrodes were chronically implanted in this songbird's cortex analogue and the neuronal activity was transmitted from unrestrained birds via a miniature FM transmitter. Frequency tuning curves (FTCs) and inhibitory sidebands were determined by presenting a matrix of frequency-level combinations of pure tones. From each FTC, the characteristic frequency (CF) and several parameters describing the neurons' filter characteristics were derived and compared to the same recording site's filter function while simultaneously stimulating with a continuous CF tone 20 dB above the response threshold. Our results show a significant improvement of frequency selectivity during two-tone stimulation, indicating that spectral filtering in the starling's auditory forebrain depends on the acoustic background in which a signal is presented. Moreover, frequency selectivity was found to be a function of the time over which the stimulus persisted, since FTCs were much sharper and inhibitory sidebands were largely expanded several milliseconds after response onset. Neuronal filter bandwidths during two-tone stimulation in the auditory forebrain are in good agreement with psychoacoustically measured critical bandwidths in the same species. Radiotelemetry proved to be a powerful tool in studying neuronal activity in freely behaving birds.

Dual-channel telemetry system for recording vocalization-correlated neuronal activity in freely moving squirrel monkeys

A miniature telemetric system is described which allows simultaneous measurements of neural activity and vocalization in freely moving monkeys within their social group. Single and multi-unit activities were detected with medium impedance electrodes that were fixed to self-made microdrives allowing accurate vertical positioning over a range of 8 mm. Vocalizations were registered by means of a piezo-ceramic device sensing the vocalization-induced skull vibrations. This allowed identification of the vocalizing animal in a larger group and eliminated environmental noise. Neuronal activity and vocalization were transmitted via separate channels of a FM transmitter using different carrier frequencies. The signals were decoded in two conventional FM receivers equipped with an automatic frequency control. The signals were stored for off-line analysis on a HiFi videotape recorder.