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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.

Center for Neural Communication Technology

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:

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.....):


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


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 

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.


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).