Increased Synchrony with Increase of a Low-Threshold Calcium Conductance in a Model Thalamic Network: A Phase-Shift Mechanism

A computer model of a thalamic network was used in order to examine the effects of an isolated augmentation in a low-threshold calcium current. Such an isolated augmentation has been observed in the reticular thalamic (RE) nucleus of the genetic absence epilepsy rat from the Strasbourg (GAERS) model of absence epilepsy. An augmentation of the low-threshold calcium conductance in the RE neurons (gTs) of the model thalamic network was found to lead to an increase in the synchronized firing of the network. This supports the hypothesis that the isolated increase in gTs may be responsible for epileptic activity in the GAERS rat. The increase of gTs in the RE neurons led to a slight increase in the period of the isolated RE neuron firing. In contrast, the low-threshold spike of the RE neuron remained relatively unchanged by the increase of gTs. This suggests that the enhanced synchrony in the network was primarily due to a phase shift in the firing of the RE neurons with respect to the thalamocortical neurons. The ability of this phase-shift mechanism to lead to changes in synchrony was further examined using the model thalamic network. A similar increase in the period of RE neuron oscillations was obtained through an increase in the conductance of the calcium-mediated potassium channel. This change was once again found to increase synchronous firing in the network.