AAWSAP DIRD, Technological Approaches to Controlling External Devices, March 2010

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NEW ELECTRODE DESIGNS
Building upon studies like Parikh et al., designs look toward invasive systems capable of
pinpointing cortical regions and monitoring their neural activity at or near single neuron
resolution. Clement et al. employed microwire neural implants to combine fMRI and
intracortical recordings to yield important information about metabolic mechanisms that
correlate with neural activity. While modeling studies have been conducted in numerous
experiments, they served as a baseline to understand the potential dangers associated
with the strong static magnetic field alone or while exposed to typical MRI protocols on
the surrounding tissue and the design of an MRI compatible electrical array (References
48, 49). On the surface this may seem a trivial task, however the study shows this is
not only a challenging design detail, but decisive in the resulting recorded data of
neural activity. Examples of the electrode designs are shown in Figure 8.
Figure 8. The Michigan Electrodes. Left: A variety of different silicon probes have been placed on the back of a
U.S. penny. The copper scaffold in the background is the array of columns on the Lincoln Memorial. Right: Four 64­
site probes have been assembled into a three-dimensional structure. (Reference 49)
Previous work addressed important issues related to short-term compatibility of silicon
microelectrodes. In that report, identification and replacement of appropriate
components of a silicon microelectrode system resulted in virtually artifact-free MR
images and stable recordings of motor unit activity, although chronic studies were not
performed (Reference 50). By utilizing this knowledge the authors designed a microwire
electrode array capable of surviving the strong magnetic fluctuations exhibited from an
fMRI. Figure 9 shows the device and its related connective components (Reference 51).
Figure 10 shows the before and after MR images when connectors and structural screws
compatible with MR are employed as well as the compatible electrodes.
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