2.4.1. Synchrony Index

(1) Voltage Synchrony Index. The degree of synchrony in the network is calculated according to the method developed by [42–45]. The population averaged voltage V(t) is defined as V(t) = (V₁(t)+⋯+V_N(t))/N, where N is the number of cells, and then the voltage synchrony index SV is computed as follows:

The synchronization measure SV is normalized between 0 and 1, and the larger value of SV implies the higher degree of synchrony in the network.

(2) Spike Synchrony Index. Another synchrony measure, Spike synchrony (SS), was computed by modifying the voltage synchrony metric presented by Golomb and Rinzel [46], using counts of spikes binned into 5 ms bins. With a_i(t) being defined as the binned spike count over time period for cell i, we computed the within cell variance σ_i² and population variance σ_pop² as follows:

where a(t) = (a₁(t)+⋯+a_N(t))/N for a population of N neurons and the brackets denote averaging over total simulation time. The synchrony measure SS was defined as:

Obviously, the larger the value of SS is, the higher the level of synchrony in the network becomes.