IONIC MECHANISMS FOR INTRINSIC SLOW OSCILLATIONS IN THALAMIC RELAY NEURONS

The oscillatory properties of single thalamocortical neurons were investigated by using a Hodgkin-Huxley-like model that included Ca2+ diffusion, the low-threshold Ca2+ current (I(T)) and the hyperpolarization-activated inward current I(h)). I(h) was modeled by double activation kinetics regulated by intracellular Ca2+. The model exhibited waxing and waning oscillations consisting of 1-25-s bursts of slow oscillations (3.5-4 Hz) separated by long silent periods (4-20 s). During the oscillatory phase, the entry of Ca2+ progressively shifted the activation function of I(h), terminating the oscillations. A similar type of waxing and waning oscillation was also observed, in the absence of Ca2+ regulation of I(h), from the combination of I(T), I(h), and a slow K+ current. Singular approximation showed that for both models, the activation variables of I(h) controlled the dynamics of thalamocortical cells. Dynamical analysis of the system in a phase plane diagram showed that waxing and waning oscillations arose when I(h) entrained the system alternately between stationary and oscillating branches.