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Facilitating the propagation of spiking activity in feedforward networks by including feedback

Fig 7

Different background activity regimes in the RPN (a, c) and FFN (b, d) networks.

The population Fano factor in the 10th layer of the RPN (a) and FFN (b), is shown as a measure of synchrony in the background network activity for different strengths of inter-layer connections (X-axis) and input rate (Y-axis). The cyan area, indicated by an asterisk, denotes a synchronous irregular regime, whereas the vast, blue area denotes the asynchronous irregular regime, with a long-tailed distribution of CVISI and low average correlation coefficients (S2 Fig). Both network types transit to the synchronous irregular regime, indicated by a black square, with increasing input rate and inter-layer connection strength. However, the RPN reaches the synchronous irregular state much earlier than the FFN. The population Fano factor in the 10th layer of the RPN (c) and FFN (d), is shown for different inter-layer connection delay (X-axis) and strength (Y-axis). The input rate was set to 8 kHz for both network types. For strong enough inter-layer connections, provided their loop delay matched the resonance period of the network, sustained background activity oscillations might develop in the network and propagate to the downstream layers. Black circles in all four panels indicate the parameter settings used to investigate the pulse packet propagation in Figs 2 and 6 and the red trace in Fig 3. In panels (a) and (b), the feedforward and feedback delays were set to 5 ms, respectively.

Fig 7

doi: https://doi.org/10.1371/journal.pcbi.1008033.g007