CELLULAR AND NETWORK MODELS FOR INTRATHALAMIC AUGMENTING RESPONSES DURING 10-HZ STIMULATION

Repetitive stimulation of the thalamus at 7-14 Hz evokes responses of increasing amplitude in the thalamus and the areas of the neocortex to which the stimulated foci project. Possible mechanisms underlying the thalamic augmenting responses during repetitive stimulation were inve stigated with computer models of interacting thalamocortical (TC) and thalamic reticular (RE) cells. The ionic currents in these cells were modeled with Hodgkin-Huxley type of kinetics, and the results of the m odel were compared with in vivo thalamic recordings from decorticated cats. The simplest network model demonstrating an augmenting response was a single pair of coupled RE and TC cells, in which RE-induced inhi bitory postsynaptic potentials (IPSPs) in the TC cell led to progressi ve deinactivation of a low-threshold Ca2+ current. The augmenting resp onses in two reciprocally interacting chains of RE and TC cells depend ed also on gamma-aminobutyric acid-B (GABA(B)) IPSPs. Lateral GABA(A) inhibition between identical RE cells, which weakened bursts in these cells, diminished GABA(B) IPSPs and delayed the augmenting response in TC cells. The results of these simulations show that the interplay be tween existing mechanisms in the thalamus explains the basic propertie s of the intrathalamic augmenting responses.