Longitudinal intrafascicular electrodes (LIFEs) are electrodes designed to be placed inside the peripheral nerve to improve stimulation selectivity and to increase the recording signal-to-noise ratio. We evaluated the functional and morphological effects of either Pt wire LIFEs or polyimide-based thin-film LIFEs implanted in the rat sciatic nerve for 3 mo. The newly designed thin-film LIFEs are more flexible, can be micromachined and allow placement of more active electrode sites than conventional Pt LIFEs. Functional results at 1 mo indicated an initial decline in the nerve conduction velocity and in the amplitude of muscle responses, which recovered during the following 2 mo towards normal values. Morphological results showed that both types of LIFEs induced a mild scar response and a focal but chronic inflammatory reaction, which were limited to a small area around the electrode placed in the nerve. Both types of LIFEs can be considered biocompatible and cause reversible, minimal nerve damage.

Among the possible interfaces with the peripheral nervous system (PNS), intraneural electrodes represent an interesting solution for their potential advantages such as the possibility of extracting spikes from electroneurographic (ENG) signals. Their use could increase the precision and the amount of information which can be detected with respect to other processing methods.In this study, in order to verify this assumption, thin-film longitudinal intrafascicular electrodes (tfLIFE) were implanted in the sciatic nerve of rabbits. Various sensory stimuli were applied to the hind limb of the animal and the elicited ENG signals were recorded using the tfLIFEs. These signals were processed to determine whether the different types of information can be decoded. Signals were wavelet denoised and spike sorted. Support vector machines were trained to use the spike waveforms found to infer the stimulus applied to the rabbit. This approach was also compared with previously used ENG processing methods.The results indicate that the combination of wavelet denoising and spike sorting techniques can increase the amount of information extractable from ENG signals recorded with intraneural electrodes. This strategy could allow the development of more effective closed-loop neuroprostheses and hybrid bionic systems connecting the human nervous system with artificial devices.

No abstract

Choi JH, Koch KP, Poppendieck W, Lee M, Shin HS. High resolution electroencephalography in freely moving mice. J Neurophysiol 104: 1825-1834, 2010. First published July 7, 2010 doi:10.1152/jn.00188.2010. Electroencephalography (EEG) is a standard tool for monitoring brain states in humans. Understanding the molecular and cellular mechanisms underlying diverse EEG rhythms can be facilitated by using mouse models under molecular, pharmacological, or electrophysiological manipulations. The small size of the mouse brain, however, poses a severe limitation in the spatial information of EEG. To overcome this limitation, we devised a polyimide based microelectrode array (PBM array) with nanofabrication technologies. The microelectrode contains 32 electrodes, weighs 150 mg, and yields noise-insensitive signals when applied on the mouse skull. The highdensity microelectrode allowed both global and focused mapping of high resolution EEG (HR-EEG) in the mouse brain. Mapping and dynamical analysis tools also have been developed to visualize the dynamical changes of spatially resolved mouse EEG. We demonstrated the validity and utility of mouse EEG in localization of the seizure onset in absence seizure model and phase dynamics of abnormal theta rhythm in transgenic mice. Dynamic tracking of the EEG map in genetically modified mice under freely moving conditions should allow study of the molecular and cellular mechanisms underlying the generation and dynamics of diverse EEG rhythms.

In the following article, the technologies to fabricate polyimide-based thin and flexible substrates with monolithically integrated electrode arrays and printed circuit boards (PCB) for hybrid electronic assemblies as well as an assembling technique that connects bare electronic dice with flexible PCBs are presented. The concept of modular, flexible biomedical microsystems as neural prostheses is introduced in general and described in detail in three examples. A cuff electrode with integrated multiplexer circuitry and standard implantable cables represents the combination of microtechnology with precision mechanics; a sieve electrode used as an implant in peripheral nerve regeneration studies demonstrates the next level of integration density but still uses a cable connection; and last, joint effort to fabricate the demonstrator of a vision prosthesis that is completely implantable in the eye with a wireless link for energy supply and data transmission is presented. System design, hybrid assembling technology, and flexible multilayer encapsulation using parylene and silicone rubber are the key components for creating a new generation of neural prostheses for complex and challenging new applications

We present the results of a 5-year patient follow-up after implantation of an original neuroprosthesis. The system is able to stimulate both epimysial and neural electrodes in such a way that the complete flexor-extensor chain of the lower limb can be activated without using the withdrawal reflex. We demonstrate that standing and assisted walking are possible, and the results have remained stable for 5 years. Nevertheless, some problems were noted, particularly regarding the muscle response on the epimysial channels. Analysis of the electrical behaviour and thresholds indicated that the surgical phase is crucial because of the sensitivity of the functional responses to electrode placement. Neural stimulation proved to be more efficient and more stable over time. This mode requires less energy and provides more selective stimulation. This FES system can be improved to enable balanced standing and less fatiguing gait, but this will require feedback on event detection to trigger transitions between stimulation sequences, as well as feedback to the patient about the state of his lower limbs.

Existing nerve monitoring devices in thyroid surgery are - except for one - mainly intermittently working nerve identification tools. We present a new vagal electrode which allows true continuous monitoring of the recurrent laryngeal nerve (RLN). The electrode was designed as a tripolar hybrid cuff electrode consisting of polyimide, gold and platinum layers embedded in a flexible silicon cuff which can be opened at the long side for introducing the nerve. It is fully implantable and atraumatic. The evoked potentials are sensed by standard thyroid electrodes. Real-time signal analysis and audio feedback are achieved by specially designed software. Homogeneous and stable signals were recorded throughout the operations. Thus real-time computer-based signal analysis was possible. Evoked potentials reached 300-900 mV. Mean time to place the cuff electrode was 5.5 min. The nerve was stimulated a mean of 63 min (range 55-99 min). No RLN lesions were detected postoperatively. The new vagal electrode was easy to handle and led to stable and reproducible signals. The stimulation current could be kept extremely low due to the special geometry of the electrode. It offers the possibility for uninterrupted, continuous laryngeal nerve monitoring in thyroid surgery. In an ongoing clinical trial its compatibility as an add-on for existing nerve monitoring devices is being tested.

It is currently not possible to record electromyographic (EMG) signals from many locations concurrently inside the muscle in a single wire electrode system. We developed a thin-film wire electrode system for multichannel intramuscular EMG recordings. The system was fabricated using a micromachining process, with a silicon wafer as production platform for polyimide-based electrodes. In the current prototype, the flexible polymer structure is 220 microm wide, 10 microm thick, and 1.5 cm long, and it has eight circular platinum-platinum chloride recording sites of 40-microm diameter distributed along the front and back surfaces with 1,500-microm intersite spacing. The system prototype was tested in six experiments where the electrode was implanted into the medial head of the gastrocnemius muscle of rabbits, perpendicular to the pennation angle of the muscle fibers. Asynchronous motor unit activity was induced by eliciting the withdrawal reflex or sequential crushes of the sciatic nerve using a pair of forceps. Sixty-seven motor units were identified from these recordings. In the bandwidth 200 Hz to 5 kHz, the peak-to-peak amplitude of the action potentials of the detected motor units was 75 +/- 12 muV and the root mean square of the noise was 1.6 +/- 0.4 muV. The noise level and amplitude of the action potentials were similar for measures separated by up to 40 min. The experimental tests demonstrated that thin film is a promising technology for a new type of flexible-wire intramuscular EMG recording system with multiple detection sites.