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Professor Normann has moved from conventional electrical engineering to retinal physiology and into cortical physiology over the past 30 years. His electrical engineering background and his interests in neurophysiology have provided unique insights into the studies of the vertebrate visual system. It has been long appreciated that the parallel processing functions of the nervous system can best be studied with tools that will allow one to examine firing patterns of large numbers of neurons or to excite large numbers of neurons via extrinsic currents. A variety of techniques have evolved which permit this parallel acquisition of information but many of these techniques have poor spatial and/or temporal resolution which limit their utility in understanding how groups of neurons work in concert. Normann and his students and colleagues have developed a unique microelectrode array which provides unprecedented spatial and temporal resolution recording of activity from large numbers of neurons in cerebral cortex and recently, in the peripheral nervous system. Because these microelectrode arrays are fabricated mainly from silicon, they have been demonstrated to be highly biocompatible: single unit recordings have been made from motor cortex in behaving primates for periods exceeding three years.
Normann and his colleagues have had to develop support systems which enable researchers to utilize these arrays to their fullest capabilities. Implantation of 100 very sharp microelectrodes cannot be achieved with manual techniques. The Normann team has developed a high velocity impulse insertion technique that allows complete insertion of the arrays with little or no cortical trauma. One is next confronted with the problem of having to deal with up to 100 channels of neural information on each array. Normann and his colleagues have developed 100 channel neural signal amplifiers that boost and, optimally filter the signals. The signals are sent to a 100-channel digital signal processing based data acquisition system. This system comprises 100 channels of data, displays on-line and in real time continuously produces raster plots from each of the 100 channels and stores this data in a conventional Pentium-class P.C.
This suite of tools has been used by Normann and his graduate students to study parallel information processing and encoding of visual information by the vertebrate retina, the cat visual cortex and monkey motor cortex. Normann and his colleagues have shown that individual ganglion cells in the turtle are relatively poor classifiers of visual features; however, small groups of ganglion cells allow for the classification of intensity into and color good fidelity. Further, Normann and his colleagues have shown that there are temporal dependencies in this encoding of visual information; response shuffling degrades the classification performance of the groups of ganglion cells. Similar temporal dependencies are seen in ensembles of cells in monkey motor cortex. In collaborative studies done with Dr. John Donoghue at Brown University, we have shown that the volitional intent of a monkey trained to play simple video games can be determined from as few as 15 neurons in motor cortex. Again, shuffled responses degrade the estimation of the monkey's performance suggesting that temporal dependencies in the firing of ensembles of M1 units are involved in the encoding of volitional intent.
These tools and their validation in animal experiments, are leading to human experiments that will be directed at the development of neuroprosthetics systems that will offer new avenues for therapy for those with damaged or diseased parts of their nervous system. Professor Normann plans to continue the development of these electrode arrays and associated technologies, using these arrays in animal experimentation and to begin this new phase of human experimentation.
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