Recording of simultaneous single-unit activity in the dragonfly ganglia

A technique for discriminating simultaneously active single units from multiple-unit data records has been developed. Multiple-unit records were obtained extracellularly from the dragonfly mesothoracic ganglion using two paired-electrode sets. The multiple-unit records were post processed based on the unique physical characteristics imparted to each spike via the tissue medium and spatial geometry of cells. It was assumed that the action potential amplitude falls off roughly as the inverse of distance squared from the recording electrode. Further, it was assumed that the tissue RC characteristics coupled with action potential amplitudes and neuron dipole characteristics impart a spike waveform unique to each cell. Accordingly, spikes were sorted by amplitude ratio as well as by matching of spike waveforms. Additional waveform characterization was derived from the spike angle (width) within grouped spikes. Decomposition of the multiple-unit records based on these parameters yielded clustered spike records from defined cellular sources. The defined clusters were combined to provide the cumulative record for a large number of simultaneously active single units.