“School of Cognitive”
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| Paper IPM / Cognitive / 14470 |
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Despite a thorough mapping of the anatomical connectivity between brain regions and decades of neurophysiological studies of neuronal activity within the various areas, our understanding of the nature of the neural signals sent from one area to another remains rudimentary. Orthodromic and antidromic activation of neurons via electrical stimulation ("collision testing") has been used in the peripheral nervous system and in subcortical structures to identify signals propagating along specific neural pathways. However, low yield makes this method prohibitively slow for characterizing cortico-cortical connections. We employed recent advances in electrophysiological methods to improve the efficiency of the collision technique between cortical areas. There are three key challenges: 1) maintaining neuronal isolations following stimulation, 2) increasing the number of neurons being screened, and 3) ensuring low-latency triggering of stimulation after spontaneous action potentials. Our system addresses these issues using recent improvements in on-line tetrode-based isolations, linear array electrodes, and the processing speed of data acquisition hardware systems. We have developed a software package for on-line isolations and stimulation triggering, which operates in conjunction with a Hardware Processing Platform (HPP). The HPP is a system on a chip solution enabling real-time re-programming. Employing the HPP programmable device for template matching both accelerates spike sorting and provides the low-latency triggering of stimulation required to produce collision trials. Recording with a linear tetrode array electrode allows simultaneous screening of multiple neurons, while the software package coordinates efficient collision testing of multiple user-selected units across channels. This high-throughput connectivity screening system will enable researchers working with a variety of animal models and brain regions to identify the functional properties of specific projections between cortical areas in behaving animals.
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