Figure 1.
Automatic detection of spontaneous synaptic events. A, Schematic illustration of detection algorithm and critical parameters. The difference between the minimum and maximum of membrane potential is computed for a time period, τ1 (equal to twice the minimum event distance, τmin). An event is detected if the difference is greater than the amplitude threshold, Fσ, where σ is the SD of the noise and F is a multiplication factor. The peak value is computed as the local maximum within the expected event duration τ2. The search for a subsequent synaptic event begins once the membrane potential decays from the peak value by ΔVm = 4σ. B, Number of events detected as a function of minimum event distance, τmin (n = 4 spiny projection neurons). Note that the number of events varies very little when τmin is reduced from 10 msec to 5 msec or increased to 15 msec. C, Scatter plot reveals no correlation between mean event amplitude and mean event frequency. This suggests that differences in event frequency between neurons are not caused by differences in event amplitude. D, Similarity of noise from perceptually synaptic input-free data segments (▪, SD, 3.4 pA) and noise from data segments in which ionotropic glutamate and GABA receptors are blocked (□, bath application of 10 μm DNQX, 50 μm APV, and local application of 10 mm picrotoxin; SD, 2.9 pA). For the population, noise SD is 2 ± 0.18 pA. E, Effect of threshold on amplitude and charge of unitary synaptic events confirms that F = 5 is the “best” threshold for PSC detection. An increase in F to 6 significantly decreases the charge and amplitude of the mean unitary PSC by >20%, whereas a decrease in F to 4 nonsignificantly increases the charge and amplitude of the mean unitary PSC by only ∼10%.