A tetrode is a bundle of four microwires that can record from multiple neurons simultaneously in the brain of a freely moving animal. Tetrodes are usually electroplated to reduce impedances from 2-3 MΩ to 200-500 kΩ (measured at 1 kHz), which increases the signal-to-noise ratio and allows for the recording of small amplitude signals. Tetrodes with even lower impedances could improve neural recordings but cannot be made using standard electroplating methods without shorting. We were able to electroplate tetrodes to 30-70 kΩ by adding polyethylene glycol (PEG) or multiwalled carbon nanotube (MWCNT) solutions to a commercial gold-plating solution. The MWCNTs and PEG acted as inhibitors in the electroplating process and created large-surfacearea, low-impedance coatings on the tetrode tips.

Aims Nanoelectrodes are an emerging biomedical technology that can be used to record intracellular membrane potentials from neurons while causing minimal damage during membrane penetration. Current nanoelectrode designs, however, have low aspect ratios or large substrates and thus are not suitable for recording from neurons deep within complex natural structures, such as brain slices. Materials & methods We describe a novel nanoelectrode design that uses nanowires grown on the ends of microwire recording electrodes similar to those frequently used in vivo. Results & discussion We demonstrate that these nanowires can record intracellular action potentials in a rat brain slice preparation and in isolated leech ganglia. Conclusion Nanoelectrodes have the potential to revolutionize intracellular recording methods in complex neural tissues, to enable new multielectrode array technologies and, ultimately, to be used to record intracellular signals in vivo.

The recording of neural ensembles in awake, behaving rats has been an extremely successful experimental paradigm, providing demonstrable scientific advances. Dynamic control of the position of the implanted electrodes is of key importance as mobile electrodes provide a better signal-to-noise ratio and a better cell/ electrode yield than nonmobile electrodes. Here we describe the use of low cost, soon to be commercially available dc motors to successfully control the depth of electrodes. The prototype designed is approximately 30 mm in diameter and 50 mm in length and weighed about 30 gms. This paper presents the results of linear displacements of electrodes achievable with this motorized microdrive.

We report our preliminary work to explore a new method of signal transmission for bio-implantable microsystems. Intra-brain communication or IBCOM is a wireless signal transmission method that uses the brain itself as a conductive medium to transmit the data and commands between neural implants and data processing systems outside the brain. Two miniaturized IBCOM (micro-IBCOM) CMOS chips were designed and fabricated for an in vivo test bed to transmit two prerecorded neural signals at different binary frequency shift keying (BFSK) carrier frequencies to validate the feasibility of IBCOM concept. The chips were packaged for full implantation in a rat brain except for external power delivery. The original neural signal waveforms were successfully recovered after being transmitted between two platinum electrodes separated by 15 mm with transmission power less than 650 pJ/bit for the CMOS implementation.

The ability to record neural ensembles from awake, behaving animals is one of the most important and successful components of the neuroscience experimental toolbox. However, even the most advanced modern systems have limitations due to the physical coupling of the recording site with the headstage. These systems can only record from a limited number of structures at any one time and have particular difficulty recording large ensembles from animals with thin skulls (e.g., mice, songbirds). Current systems cannot record from fragile structures (spinal cord, peripheral nerves and ganglia) during behavior because the wire electrodes would shred the fragile nerves as the animal moves. We propose the concept of a neural nanoprobe that is physically decoupled from a separately implanted waystation. Because the nanoprobes are not connected to the waystation by physical wires, multiple nanoprobes could be placed in multiple neural structures, all transmitting to a single, separate waystation. Because the nanoprobes effectively float in the cellular matrix, they are safe to put in fragile structures. The waystation does not need to be implanted in the fragile structures; it only needs to be electrically coupled to them. The first step to the realization of this device is a low-power, high-fidelity method for communicating between the nanoprobe and the waystation. In this abstract, we report a successful test proving the viability of using the brain itself as the conducting medium through which the nanoprobe and waystation can communicate. Initial tests show that neural signals from multiple transmission sites can be sent to a single, separated receiver. We first identified the current-loss of sine-waves transmitted through live (anesthetized) brain tissue. We found negligible current-loss across frequencies ranging from 100 kHz–50 MHz across distances as much as 15 mm. As these frequencies are larger than any known frequencies used by neural signals, they are unlikely to interfere with neural function. We next measured the ability to transmit and receive pre-recorded neural signals (sampled at 20 kHz), using pre–recorded signals to determine the fidelity of transmission. The two different signals were transmitted, received, and successfully demodulated with high-fidelity, even with transmission currents as low as 2 μA. Both the transmitters and the receiver each had their own battery power supply to ensure that they used separate, floating grounds. Finally, to ensure that the intra-brain communication signals did not interfere with neural activity, we recorded extra-cellular potentials before, during, and after the test. No changes were observed in spike shape, spike frequency, bursting, or other cellular properties, demonstrating the safety of this technique. Supported by a grant from the Institute for Engineering in Medicine (U Minnesota) and training grant support from T90-DK070106. Corresponding author; email: redish@umn.edu