Stability Characteristics of Positive Feedback in a Neural Population

Glomerular neurons were driven by single shock stimulation of the primary olfactory nerve (PON). The poststimulus time (PST) histograms showed a rapid increase in pulse probability to a crest, followed by an exponential decay to background level P
0
. The crest magnitude and decay rate both increased with increasing stimulus intensity. The decay rate was extrapolated to zero at threshold. This implies that loop gain is unity at and below threshold.