Artifactual synchrony via capacitance coupling in multi-electrode recording from cat striate cortex

Elucidation of neural connectivity patterns in the brain are thought to give us a mechanistic understanding of how the brain works. Functional connectivity is best studied by simultaneous recording of single-unit activity from many neurons. Accordingly, various types of multiple-microelectrode systems have been developed. We have studied long-range lateral interactions in cat striate cortex. To physiologically characterize interacting cells recorded simultaneously, we used two microelectrodes whose movements were controlled by two independently-movable microdrives. The tips of the two microelectrodes were separated by ∼2 mm or more. During preliminary plotting of two receptive fields of cell pairs, we often noted the emergence of perfectly synchronous firing between two spike trains (amplitude ratio, about 20:1) registered with two microelectrodes. Synchronously firing, smaller spikes disappeared when larger spikes of the pair were lost to either substantial advancement of or placing an electrolytic lesion at the electrode registering the latter. The synchrony also disappeared when two microdrive systems were shielded individually. We concluded that the synchrony was attained through capacitance coupling between two microdrive systems. We proposed a few practical recommendations to avoid the contamination of cross correlograms with the false-positive, narrow peak at time zero due to the presence of reflected spike trains.