COMPUTATIONAL MODELS OF THALAMOCORTICAL AUGMENTING RESPONSES

Repetitive stimulation of the dorsal thalamus at 7-14 Hz produces an i ncreasing number of spikes at an increasing frequency in neocortical n eurons during the first few stimuli. Possible mechanisms underlying th ese cortical augmenting responses were analyzed with a computer model that included populations of thalamocortical cells, thalamic reticular neurons, up to two layers of cortical pyramidal cells, and cortical i nhibitory interneurons. Repetitive thalamic stimulation produced a low -threshold intrathalamic augmentation in the model based on the deinac tivation of the low-threshold Ca2+ current in thalamocortical cells, w hich in turn induced cortical augmenting responses. In the cortical mo del, augmenting responses were more powerful in the ''input'' layer co mpared with those in the ''output'' layer. Cortical stimulation of the network model produced augmenting responses in cortical neurons in di stant cortical areas through corticothalamocortical loops and low-thre shold intrathalamic augmentation. Thalamic stimulation was more effect ive in eliciting augmenting responses than cortical stimulation. Intra cortical inhibition had an important influence on the genesis of augme nting responses in cortical neurons: A shift in the balance between in tracortical excitation and inhibition toward excitation transformed an augmenting responses to long-lasting paroxysmal discharge. The predic tions of the model were compared with in vivo recordings from neurons in cortical area 4 and thalamic ventrolateral nucleus of anesthetized cats. The known intrinsic properties of thalamic cells and thalamocort ical interconnections can account for the basic properties of cortical augmenting responses.