Dynamics of spike threshold in a two-compartment neuron with passive dendrite

• Spike threshold of a two-compartment neuron model is determined within a range of dVS/dt.
• Effects of morphology and internal coupling conductance on threshold dynamics are studied.
• Biophysical basis associated with each threshold dynamics is investigated.
• Threshold dynamics is conceptualized as the outward level of net current at perithreshold potentials.

Here a two-compartment model is used to investigate how spike threshold depends on the rate of membrane depolarization leading to the action potential, i.e., dVS/dt. The model is comprised of a soma and a passive dendrite, and incorporates a morphological parameter that describes the area proportion occupied by soma. The threshold potential of somatic chamber is determined within a range of dVS/dt for different values of morphological parameter and internal coupling conductance. By analyzing the interactions of inward and outward membrane currents prior to spike initiation, the biophysical basis associated with each threshold dynamic has been identified. Based on the simulations, we conceptualize the threshold dynamics of neuron as the outward level of somatic net current at the perithreshold potentials. These results provide a detailed description about how the morphology and biophysics of neurons participate in their threshold dynamics, which could facilitate to interpret the modulatory mechanism of subthreshold electromagnetic fields as well as the biophysical basis of neural coding.