High resolution detection of stationary and evolving two-dimensional current source density within neuronal microcircuits

The use of a high-density microelectrode array (>4,000 microelectrodes) allows the recording of evoked and ongoing field activity of the whole hippocampal formation and other tissues with high spatiotemporal resolution. From these recordings, it is possible to obtain the current source density (CSD), which separates the current generators into sinks and sources; this differentiation provides the means to distinguish correlated, disjoint loci of activity and track them separately at near-to-cell resolution. By obtaining the vectorial average of an area regarded as a sink or source, we obtain a putative center of action or center of mass that can be traced in time. Thus, successive centers would reveal the immediately nearby correlated units that "inherit" or otherwise are affected by this activity, revealing a putative route of transfer of information that can be quantitated with high spatiotemporal definition. For structured tissues, this methodology provides a means to infer effective information transmission with clear parameters that can be further analyzed in several ways. Importantly, the CSD over time reveals patterns of activity obscured by the representation of activity in the voltage domain, which can aid in uncovering synaptic interactions in restricted microcircuits.<b>NEW & NOTEWORTHY</b> We developed a novel methodology to analyze electrophysiological recordings obtained from hippocampal slices with a high-density microelectrode array. Current generators are separated into sinks and sources, and disjoint components are identified within active loci in the hippocampal substructures. A center of mass is obtained from each component, which can be tracked in time at near-cell resolution, revealing a putative route of transfer of information that can be quantitated with high spatiotemporal definition.