Figure 4. The level of inhibition determines whether temporal coherence or synaptic drive controls postsynaptic spike times in the IAF model.

Color shades indicate fraction of trials in which P1 out-competed P2: red = 100%, black = 0%. (A) At the lowest amplitude of inhibition, the range of initial synaptic strength ratios (ISS_P2/P1) over which the temporally more coherent P1 pathway can compete with the stronger but less coherent P2 pathway is narrow (between 1–1.2) and restricted to a subset of OD class 4 cells. At a high level of inhibition, the range of ISS_P2/P1 ratios over which P1 successfully out-competed P2 above chance level (0.5) is extended to include the full spectrum of OD class 4 and the majority of class 2/3 cells. In this case, pathway temporal coherence (σ⁻¹) between the two pathways was set to a ratio of 1∶2 (P1:P2). (B) The influence of inhibition holds for a range of temporal coherence pathway ratios. (C) Increased inhibition had a similar influence when contralateral bias was implemented as a difference in number of synaptic inputs, rather than initial synaptic strength, P2/P1 ratios ranging from 1 to 3 were tested. (D) The ability of increasing inhibition to provide a competitive advantage to P1 over P2 is maintained in an implementation of weight-dependent STDP. In this case, the amount of potentiation for a given LTP event was inversely related to synaptic strength A₊ * (1-α), see Methods for more details.