Development of a miniaturized, reconnectable, and implantable multichannel connector.

Objective. Connectors for implantable neural prosthetic systems provide several advantages such as simplification of surgery, safe replacement of implanted devices, and modular design of the implant systems. With the rapid advancement of technologies for neural implants, miniaturized multichannel implantable connectors are also required. In this study, we propose a reconnectable and area-efficient multichannel implantable connector.Approach. A female-to-female adapter was fabricated using the thermal-press bonding of micropatterned liquid crystal polymer films. A bump inside the adapter enabled a reliable electrical connection by increasing the contact pressure between the contact pads of the adapter and the inserted cable. After connection, the adapter is enclosed in a metal case sealed with silicone elastomer packing. With different sizes of the packings, leakage current tests were performed under accelerated conditions to determine the optimal design for long-term reliability. Repeated connection tests were performed to verify the durability and reconnectability of the fabricated connector. The connector was implanted in rats, and the leakage currents were monitored to evaluate the stability of the connectorin vivo. Main results. The fabricated four- and eight-channel implantable connectors, assembled with the metal cases, had a diameter and length of 6 and 17 mm, respectively. Further, the contact resistances of the four- and eight-channel connectors were 53.2 and 75.2 mΩ, respectively. The electrical contact remained stable during repeated connection tests (50 times). The fabricated connectors with packings having 125%, 137%, and 150% volume ratios to the internal space of the metal case failed after 14, 88, and 14 d, respectively, in a 75 °C saline environment. In animal tests with rats, the connector maintained low leakage current levels for up to 92 d.Significance. An implantable and reconnectable multichannel connector was developed and evaluated. The feasibility of the proposed connector was evaluated in terms of electrical and mechanical characteristics as well as sealing performance. The proposed connector is expected to have potential applications in implantable neural prosthetic systems.

Current Stimulation of the Midbrain Nucleus in Pigeons for Avian Flight Control.

A number of research attempts to understand and modulate sensory and motor skills that are beyond the capability of humans have been underway. They have mainly been expounded in rodent models, where numerous reports of controlling movement to reach target locations by brain stimulation have been achieved. However, in the case of birds, although basic research on movement control has been conducted, the brain nuclei that are triggering these movements have yet to be established. In order to fully control flight navigation in birds, the basic central nervous system involved in flight behavior should be understood comprehensively, and functional maps of the birds' brains to study the possibility of flight control need to be clarified. Here, we established a stable stereotactic surgery to implant multi-wire electrode arrays and electrically stimulated several nuclei of the pigeon's brain. A multi-channel electrode array and a wireless stimulation system were implanted in thirteen pigeons. The pigeons' flight trajectories on electrical stimulation of the cerebral nuclei were monitored and analyzed by a 3D motion tracking program to evaluate the behavioral change, and the exact stimulation site in the brain was confirmed by the postmortem histological examination. Among them, five pigeons were able to induce right and left body turns by stimulating the nuclei of the tractus occipito-mesencephalicus (OM), nucleus taeniae (TN), or nucleus rotundus (RT); the nuclei of tractus septo-mesencephalicus (TSM) or archistriatum ventrale (AV) were stimulated to induce flight aviation for flapping and take-off with five pigeons.

Investigation of stereotactic surgery for avian brain stimulation by a fully implanted wireless system.

OBJECTIVE: The authors' goal was to study avian motor brain mapping via wireless stimulation to induce certain behaviors. In this paper, the authors propose an electrode design that is suitable for avian brain stimulation as well as a stereotactic implant procedure for the proposed electrode. METHODS: An appropriate breed for avian brain study was chosen. A fully implantable remote-controlled electrical stimulation system was inserted to minimize discomfort. A suitable electrode design and stereotactic surgery method based on the electrode design were investigated. RESULTS: Using a wireless stimulation system, flapping and rotation behaviors were induced by stimulating the ventral part of the nucleus intercollicularis and formatio reticularis medialis mesencephali both on the ground and during flight. CONCLUSIONS: The authors were able to implant the entire brain stimulation system inside the avian body without any surgical complications. Postoperative observations suggested that the bird did not find the implant uncomfortable.

A handheld neural stimulation controller for avian navigation guided by remote control.

BACKGROUND: Animal learning based on brain stimulation is an application in a brain-computer interface. Especially for birds, such a stimulation system should be sufficiently light without interfering with movements of wings. OBJECTIVE: We proposed a fully-implantable system for wirelessly navigating a pigeon. In this paper, we report a handheld neural stimulation controller for this avian navigation guided by remote control. METHODS: The handheld controller employs ZigBee to control pigeon's behaviors through brain stimulation. ZigBee can manipulate brain stimulation remotely while powered by batteries. Additionally, simple switches enable users to customize parameters of stimuli like a gamepad. These handheld and user-friendly interfaces make it easy to use the controller while a pigeon flies in open areas. RESULTS: An electrode was inserted into a nucleus (formatio reticularis medialis mesencephalic) of a pigeon and connected to a stimulator fully-implanted in the pigeon's back. Receiving signals sent from the controller, the stimulator supplied biphasic pulses with a duration of 0.080 ms and an amplitude of 0.400 mA to the nucleus. When the nucleus was stimulated, a 180-degree turning-left behavior of the pigeon was consistently observed. CONCLUSIONS: The feasibility of remote avian navigation using the controller was successfully verified.

CNT bundle-based thin intracochlear electrode array.

OBJECTIVE: It is known that the insertion of the intracochlear electrode is critical procedure because the damage around cochlear structures can deteriorate hearing restoration. To reduce the trauma during the electrode insertion surgery, we developed a thin and flexible intracochlear electrode array constructed with carbon nanotube (CNT) bundles. METHODS: Each CNT bundle was used for an individual electrode channel after coated with parylene C for insulation. By encapsulating eight CNT bundles with silicone elastomer, an 8-channel intracochlear electrode array was fabricated. The mechanical and electrochemical characteristics were assessed to evaluate the flexibility and feasibility of the electrode as a stimulation electrode. The functionality of the electrode was confirmed by electrically evoked auditory brainstem responses (eABR) recorded from a rat. RESULTS: The proposed electrode has a thickness of 135 µm at the apex and 395 µm at the base. It was demonstrated that the CNT bundle-based electrodes require 6-fold the lower insertion force than metal wire-based electrodes. The electrode impedance and the cathodic charge storage capacitance (CSCc) were 2.70 kΩ âˆ -20.4° at 1 kHz and - 708 mC/cm2, respectively. The eABR waves III and V were observed when stimulation current is greater than 50 µA. CONCLUSION: A thin and flexible CNT bundle-based intracochlear electrode array was successfully developed. The feasibility of the proposed electrode was shown in terms of mechanical and electrochemical characteristics. A proposed CNT bundle-based intracochlear electrode may reduce the risk of trauma during electrode insertion surgery.

A Fully Implantable Wireless Stimulation System for Pigeon Navigation.

Navigation of freely moving animals has been studied for potential application to emergency situations and hazardous environments. A fully implantable stimulation system for remote animal navigation was proposed and applied to living pigeons. The animal navigation system, consisting of an external controller and a neural stimulator, was designed based on the anatomy of the pigeons. Depth electrodes were fabricated based on the anatomy of target pigeon brain regions. The fabricated neural stimulators received data wirelessly from the external controller and generated biphasic current pulses with preset parameters of amplitude, duration, and rate. The average impedance of the fabricated electrodes was 12.0∠-13.05° kΩ at 1 kHz. The neural stimulator was implanted on the dorsal side, and the depth electrodes were inserted into the formatio reticularis medialis mesencephali (FRM). When successive current pulses with an amplitude of 400 µA, a rate of 58 Hz, and a duration of 80 µs were applied to the target regions at 0.85 s intervals, turning/circling behaviors were induced for 6.2 s. The feasibility of the proposed wireless stimulation system was demonstrated in vivo.

Locomotion Control of Pigeons using Polymer-based Deep Brain Electrodes.

This paper describes the electrical modulation of locomotion in pigeons using deep brain electrodes. Polymer-based depth electrodes with four channels were fabricated. Based on the location of the nucleus intercollicularis (ICo), the shanks of the depth electrodes were designed to be a length of 11 mm. After the implantation of the depth electrode into the ICo region of the brain, it was connected by wires to a custom-made stimulator, and biphasic current pulses were delivered. Current pulses with an amplitude of 0.5 mA, a rate of 58.0 Hz, and a duration of $320\mu \mathrm{s} $s were applied for 0.5 s. When the ICo region was electrically stimulated, taking-off behavior was successfully induced for 0.4 s. Induction of taking-off behavior by electrical stimulation, when coupled to control of turning and running forward locomotions, may contribute to the development of remote flight-control system of freely moving pigeon.