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# STILL BELIEVE HUMAN IMPLANTATION FOR BOTH TELEMETRY AND CONTROL ("STIMULATION") IS SOMEONE'S OVERACTIVE IMAGINATION?

Original link: http://www.engin.umich.edu/facility/cnct/orgind.html

Scroll down below this main CNCT page for additional details transcribed by one of our CAHRA members.

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Center for Neural Communication Technology
Organization

The NIH NCRR requires that its Centers have several basic components: internal research projects, collaborative research projects, and service to external investigators in the form of distribution and training. The organization of the Center for Neural Communication Technology (CNCT) will be described here with links to more details on individual projects.

The underlying goal for all of the work conducted by the CNCT is to make multichannel recording and stimulation devices available to researchers which will enable them to more efficiently communicate with the brain. Micromachined electrodes offer the potential to extend small ensemble studies to tissue volume studies consisting of dozens if not hundreds of cells.

Internal Research Projects

There are three internal research projects under the Center which are designed to enhance the capability of the base technology:

- Project 1, Extensions of Micromachined Microelectrode Technology : Extend the basic structure of the device to include fluid carrying channels for delivery of fluids to tissue volume, and/or to lesion at recording/stimulation site locations.

- Project 2, Biological Neural Networks: Develop techniques for data acquisition from and analysis of neural circuits in the volume surrounding arrays of recording devices. The direction which has been proposed for this project over the next grant period will be to study the relationships between the physical characteristics of the devices and the architecture of the neural tissue to rationalize the process of design and experimentally explore and model the deterioration of chronic implants over time to improve their behavior. A recent poster presentation on data collected from the cochlear nucleus can be seen here .

- Project 3, Morphological Visualization and Assessment : Explore the envelope of tissue surrounding stimulation, recording and/or chemical delivery probes for histological evidence of deterioration of probe performance which has been observed electrophysiologically in vivo.

Collaborative Research Projects

In addition to internal projects, there are multiple collaborative research projects with investigators outside the Center. Collaborators contribute significantly toward improving and expanding the use of the technology in areas including optimization of device designs, evaluation of chronic connectors, interconnects and cranial chambers, improvement of implantation methods, development of protocols for chronic electrode site maintenance, testing of advanced devices, and exploration of new application areas.

Here are links to webpages of some of our collaborators (more to come.....):

- Gyorgy Buzsaki, M.D., Ph.D. , Rutgers University, Neural network activity in the hippocampal formation

- Steven Highstein, M.D. Ph.D. , Washington University, Effects of microgravity upon the labyrinth

- David Martin, Ph.D. , University of Michigan, Microstructure and processing of bioactive protein polymers

- John Middlebrooks, Ph.D. , University of Michigan, Cortical representation of auditory space

Service

Service to investigators outside of the CNCT is provided in the forms of distribution of probes, and training in their use.

- Distribution has been a key component of the CNCT since its inception. In fact, it provided the main motivation for applying for the first NIH NCRR grant in 1994. To receive probes, we require that investigators fill out an application. Details of the variety of devices which we offer to the research public are outlined in a catalog. Standard devices are provided packaged appropriate for acute use. Prior to receiving additional batches of probes, we require the submission of a feedback form so that we may track progress and use the data to better understand and improve the technology.

- The CNCT offers several training opportunities to provide education and experience in the design, handling and application of multichannel probes.

TRANSCRIPTION OF FURTHER CNCT SITE DETAILED TEXT:

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    With support from the NIH/NCRR, the Center for Neural Communication
    Technology (CNCT) is able to offer a variety of probes to
    neuroscientists. The fabrication process for these probes gives great
    freedom in their design for recording and stimulation in the central
    nervous system. Their small size and fine features permit multichannel
    interaction with the tissue on a scale that approaches the size of the
    cells of interest.

    While the probes are not the perfect tool for every application, they do
    offer several advantages over conventional electrodes. These include
    batch fabrication which leads to very reproducible geometrical and
    electrical characteristics, the ability to include multiple sites on a
    single substrate at accurate dimensional relationships to one another,
    the capacity to integrate a multichannel interconnect for chronic
    applications, the potential for inclusion of on-chip electronics for
    signal conditioning and/or stimulus generation, and the ability to
    produce virtually any two-dimensional shape. The extensive design
    freedom offered by the technology has resulted in a variety of different
    probes which should satisfy the needs of investigators in many different
    disciplines. If you would like to receive probes from the CNCT, please
    fill out an application form .

    The distribution of passive probes to investigators both internal and
    external to the University of Michigan began in late 1988. One of our
    goals has been to obtain information on how the probes perform in a
    variety of applications, and to use this information to further optimize
    their design. The probes are currently available free-of-charge through
    support from the NIH National Center for Research Resources. The only
    method of "payment" which is currently required from users is feedback
    on probe performance to aid in the continuing effort to better
    understand and improve the technology.

    Acute Probes

    Since acute probes are generally available in greater numbers, are
    simple to package, and are easy to handle, they are a good entry point
    to using the technology. A schematic of an acute probe and its basic
    features is shown in Figure 1. The different acute designs offered in
    the catalog (available for download in pdf format, or email
    jfh@umich.edu for a hardcopy) vary in the number of shanks, the length
    and width of the shanks, and in the spacing and surface area of the
    conductive sites.

    Acute probes are mounted and electrically connected to PC boards using
    ultrasonic bonding as shown in Figure 2. Exposed connections are
    stabilized and insulated with epoxy. The pins on the PC board mate
    directly to standard integrated circuit DIP sockets permitting easy
    handling and connection. Such a socket is mounted on the front end of
    our custom-designed preamplifier (see below) and connected to high-input
    impedance amplifiers. The preamplifier is designed to be mounted on a
    microdrive directly above the animal preparation. In this way, the
    entire electrode package can be lowered to the preparation with minimal
    handling and precise electrode insertion can be achieved. This acute
    packaging scheme has proven to work well for most preparations and is
    provided as a standard item. We will, however, provide custom acute
    packaging for users who provide their own connectors.

    Once packaged, the probe site impedances are tested at 1kHz in saline.
    The investigator is provided with the impedance characteristics for each
    probe, and a site map which relates the sites on the probe to the pins
    on the PC board. Maps are also available for download. Probes are
    typically provided in groups of 6-10.

    Chronic Probes

    Many investigators are interested in performing chronic experiments. We
    currently offer chronic probes only to CNCT collaborators and to
    investigators who have gained experience with acute probes and who are
    willing to work with us to understand and improve chronic recordability.
    Recording sites on chronic probes tend to increase in impedance and
    degrade in recording quality over time. Internal Research Project 2 is
    aimed at understanding this degradation, and developing ways to prevent
    or remedy it. We hope to bring chronic probes into the general
    distribution effort in the near future.
    For a floating electrode configuration, chronic assemblies utilize a
    probe with an integrated flexible silicon ribbon cable as the
    interconnect (Figure 3). In this configuration, the probe shank is
    inserted into tissue and the flexible cable forms the interconnect to
    the percutaneous connector. Probes have also been packaged for
    investigators in non-floating chronic configurations. In this case, a
    non-cabled probe is attached directly to the percutaneous connector.

    Custom Design

    Some investigators wish to obtain devices which are designed
    specifically for their application. In fact, many of the devices in our
    catalog are based on designs that were submitted by investigators
    external to the CNCT. Custom design is a service which is offered by the
    Center to investigators who, through experience with existing designs,
    have determined that a special design is required for their study. New
    design runs occur approximately once a year with up to 20 designs per
    run.

    Site Impedance: Testing and Reduction

    The probes in the CNCT catalog have sites of two surface areas: 177
    and 1250 sq micrometer. Typically, the smaller sites are used for
    recording and the larger for stimulation. All sites are made of
    sputtered iridium. Typical impedance ranges are 2 to 3 megohms for
    recording sites and several hundred kohms for stimulation sites.
    When you receive packaged probes from the CNCT, you will also
    receive a data sheet with 1kHz site impedances. The measurements
    are made in phosphate buffered saline using an HP 4194A Gain/Phase
    analyzer. If users wish to bond their own probes or modify the
    sites in any way, an AC impedance tester is recommended.  In
    choosing or building a system, it is important that current passed
    through the probe site is very low. There are several suitable
    systems commercially available including one by Frederick Haer
    (#40-60-2) which uses 10nA measurement current).  Iridium sites can
    be modified electrochemically to increase their current passage
    capabilities, or to decrease their impedance. This is done through
    formation of an oxide on the surface by cycling a voltage across
    the iridium/electrolyte interface. The process is known as
    activation . The resulting iridium oxide has a high charge
    capacity, is resistant to dissolution and corrosion during
    stimulation, and has a lower impedance than pure iridium.

    Activation is required for those users who will be passing appreciable
    current through the sites to prevent deterioration of the metal. The
    charge injection limit of activated iridium is several hundred times
    that of unactivated iridium. Activation also has merits when applied to
    recording electrodes; for those users who wish to reduce and impedance,
    small sites can be reduced by several orders of magnitude. This may be
    especially important when minimizing crosstalk is critical such as for
    CSD analysis and when a long probe shank is required.

    Amplifiers

    Use of an appropriate headstage amplifier is critical to maximize signal
    quality from the small, high impedance sites on the probe. Important
    characteristics for such a headstage include high input impedance and
    close proximity to the probe to minimize signal loss and crosstalk, and
    low bias current to prevent damage to the sites. At the University of
    Michigan Kresge Hearing Research Institute, probes are used with custom
    built high impedance buffer amplifiers (Figure 4). The design uses the
    Texas Instruments TLC2274CD quad op amp in a DC coupled, non-inverting,
    unity gain configuration. The design incorporates SOIC packages and
    surface-mounted passive devices on a double-sided printed circuit board
    to minimize the size of the final package. The probe can be connected to
    the board with a standard DIP socket.

    A 10kohm resistor in each input circuit protects the op amp from damage
    by static discharge. A 100ohm resistor in each output circuit prevents
    oscillation when driving long cables. To prevent oscillations, increase
    slew rates, and lower output noise, 4.7 mfd tantalum capacitors, in
    parallel with 0.1 mfd ceramic capacitors, are connected as close as
    possible between each of the TLC2274 power supply pins, and the power
    supply common. The headstage can be powered from an AC/DC power supply,
    or from batteries. The power supply voltage range can be +/- 2.2 VDC to
    +/- 8 VDC at 1.5mA per channel. The power supply common can be connected
    to earth, or isolated. If isolated, an isolation stage must be provided
    in a secondary amplifier.

    An aluminum case protects the circuit and provides electrical shielding.
    The case is mounted on a non-conductive rod to isolate it from the
    micromanipulator. The headstage case and connecting cable shield should
    be connected to earth for best shielding from 60 Hz pickup. If the
    headstage power supply is to be isolated, the case should be
    electrically isolated from the experimental animal.

    While the CNCT currently does not offer these headstages, questions
    about their design and construction, or about choosing an appropriate
    commercial headstage, can be directed to the technical support email
    group (cnctsupport@umich.edu).
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