NITRO Lablog

Birch2007

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G Schalk, K J Miller, N R Anderson, J A Wilson, M D Smyth, J G Ojemann, D W Moran, J R Wolpaw and E C Leuthardt

Abstract. We show here that a brain–computer interface (BCI) using electrocorticographic activity (ECoG) and imagined or overt motor tasks enables humans to control a computer cursor in two dimensions. Over a brief training period of 12–36 min, each of five human subjects acquired substantial control of particular ECoG features recorded from several locations over the same hemisphere, and achieved average success rates of 53–73% in a two-dimensional four-target center-out task in which chance accuracy was 25%. Our results support the expectation that ECoG-based BCIs can combine high performance with technical and clinical practicality, and also indicate promising directions for further research.

Williams JC, Hippensteel JA, Dilgen J, Shain W - JNE 07

A series of animal experiments was conducted to characterize changes in the complex impedance of chronically implanted electrodes in neural tissue. Consistent trends in impedance changes were observed across all animals, characterized as a general increase in the measured impedance magnitude at 1 kHz. Impedance changes reach a peak approximately 7 days post-implant. Reactive responses around individual electrodes were described using immuno-and histo-chemistry and confocal microscopy. These observations were compared to measured impedance changes. Several features of impedance changes were able to differentiate between confined and extensive histological reactions. In general, impedance magnitude at 1 kHz was significantly increased in extensive reactions, starting about 4 days post-implant. Electrodes with extensive reactions also displayed impedance spectra with a characteristic change at high frequencies. This change was manifested in the formation of a semi-circular arc in the Nyquist space, suggestive of increased cellular density in close proximity to the electrode site. These results suggest that changes in impedance spectra are directly influenced by cellular distributions around implanted electrodes over time and that impedance measurements may provide an online assessment of cellular reactions to implanted devices.

Frampton JP, Hynd MR, Williams JC, Shuler ML, Shain W - JNE 07

One limitation to the use of neuroprosthestic devices for chronic application, in the treatmentof disease, is the reactive cell responses that occur surrounding the device after insertion.These cell and tissue responses result in increases in device impedance and failure of the device to interact with target populations of neurons. However, few tools are available to assess which components of the reactive response contribute most to changes in tissue impedance. An in vitro culture system has been developed that is capable of assessing individual components of the reactive response. The system utilizes alginate cell encapsulation to construct three-dimensional architectures that approach the cell densities found in rat cortex. The system was constructed around neuroNexus acute probes with on-board circuitry capable of monitoring the electrical properties of the surrounding tissue. This study demonstrates the utility of the system by demonstrating that differences in cell density within the three-dimensional alginate constructs result in differences in resistance and capacitance as measured by electrochemical impedance spectroscopy. We propose that this system can be used to model components of the reactive responses in brain tissue, and that the measurements recorded in vitro are comparable to measurements recorded in vivo.

Microfluidic Gene Expression

Two papers have been accepted and printed in the December 2007 edition of the Journal of Neural Engineering, in cooperation with the Wadsworth Center.

 Complex impedance spectroscopy for monitoring tissue responses to inserted neural implants.

 Three-dimensional hydrogel cultures for modeling changes in tissue impedance around microfabricated neural probes.

Wolpaw 2002 - Review of BCIs

A new movie, “The Diving Bell and the Butterfly,” has recently been released detailing the life of Jean-Dominique Bauby, the former editor of Elle magazine, who suffered from locked-in syndrome. Using his only remaining movement, blinking his eye, he wrote the book of the same name over a period of months, letter by letter. This story is often cited as one of the inspirations for brain-computer interface research, and our BCI program is working on developing new communications systems, such as integrating Dasher and BCI2000. The video link shows an example of how a BCI could be used by a person with locked-in syndrome for writing.

Dasher Video

This paper describes a new method of calculating CSDs from LFPs.