Figure 1. Detection of extracellular spikes.

Extracellular signals (top trace) were passed through an ‘up-only’ digital filter generating a signal (middle trace) that retained the fast spike rising phase. The filter used the formula shown in the inset, with f the original signal, g the processed trace and dt the time step. For each dt value, g was increased by df when df was positive, but was null when df was negative. A threshold applied to both the amplitude and rate of rise of the filtered signal permitted measurement of both the timing and the amplitude of detected spikes (bottom trace). Note that three discrete spikes were extracted from the final group of three events.