External currents

Both principal cells and interneurons receive excitatory inputs from neighboring areas as background input, such as directly from the MS via glutamatergic and cholinergic projections and indirectly from the hippocampus via deep layers of mEC.^12,26 Moreover, interneurons also receive GABAergic input from the MS, which is shown to be rhythmic.²⁶ Noise is introduced to mimic both the intrinsic and extrinsic stochasticity.⁶⁷ Thus, the external currents read:

The excitatory background inputs are constant, i.e., IBackE = 750 pA and IBackI = 325 pA. Two cases of MS GABAergic inputs to interneurons are considered: 1) I_MS(t) = I_MS,0 = -100 pA, which is the default setup; 2) I_MS(t) = I_MS,0 + Acos(2πf_MSt), where A and f_MS are the amplitude and frequency of the oscillatory input. The noise current is independent of each other and described by the Ornstein-Uhlenbeck process:^67,68

where n_i(t) is the Gaussian white noise with zero mean and unit standard deviation, η_Noise = 150 pA (standard deviation of the noise) and τ_Noise = 2 ms (time constant of the noise). Another form of input and noise currents is also modeled to exclude the dependence of main conclusions on the concrete form of external input (see Supplemental materials and methods).