Analysis of the role of the low threshold currents I(T) and I(h) in intrinsic delta oscillations of thalamocortical neurons

Thalamocortical neurons are involved in the generation and maintenance of brain rhythms associated with global functional states. The repetitive burst firing of TC neurons at delta frequencies (1–4 Hz) has been linked to the oscillations recorded during deep sleep and during episodes of absence seizures. To get insight into the biophysical properties that are the basis for intrinsic delta oscillations in these neurons, we performed a bifurcation analysis of a minimal conductance-based thalamocortical neuron model including only the I(T) channel and the sodium and potassium leak channels. This analysis unveils the dynamics of repetitive burst firing of TC neurons, and describes how the interplay between the amplifying variable m(T) and the recovering variable h(T) of the calcium channel I(T) is sufficient to generate low threshold oscillations in the delta band. We also explored the role of the hyperpolarization activated cationic current I(h) in this reduced model and determine that, albeit not required, I(h) amplifies and stabilizes the oscillation.