Figure 3.

Mode prediction for weak averaged coupling. The solid black curve is the effective coupling function K(ϕ) for the system composed of the two neurons from Fig. 3 whose intrinsic periods have a ratio of exactly 2:1 for weak coupling with g_syn = 0.01 mS/cm². The lack of zero crossing shows that they cannot lock unless the intrinsic frequency of one neuron is modified. The dashed curves are the coupling function Q(ϕ) computed with additional current to the fast neuron to change its intrinsic frequency sufficiently to enable a locking. The range of current added to the fast neuron (−0.026 μA/cm² for the top dashed curve and −0.0385 μA/cm² for the lower dashed curve) that enables these curves to have a zero crossing of the x axis determines the lower and upper limits of the intrinsic frequency of the fast neuron that allow a locking. The region inside the dashed curves is the existence region for this weak coupling strength. The upward zero crossings indicate the phases (separated by ∼0.5) at which the slow neuron receives an input from the fast neuron in a stable 2:1 locking for the coupled system.