Thalamic and thalamocortical mechanisms underlying 3 Hz spike-and-wave discharges

Alain Destexhe, David A. McCormick and Terrence J. Sejnowski

Progress in Brain Research 121: 289-307, 1999.

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Paroxysmal ~3 Hz oscillations occur in thalamic and thalamocortical circuits during petit mal or absence epilepsy. Experiments in thalamic slices have revealed first, that thalamic circuits can generate oscillations at ~3 Hz following the application of antagonists of GABA_A receptors and second, that the genesis of these oscillations is critically dependent on GABA_B-mediated inhibition in thalamic relay neurons. The ionic mechanisms that are responsible for paroxysmal oscillations in thalamic slices can be explored in detailed models based on the known biophysical properties of thalamic neurons and the various types of synaptic currents that mediate interactions between them. These models, which provide a basic explanation for the frequency of the oscillations and the conditions that promote them, have been extended to include thalamocortical interactions. The recurrent excitation in the cortex and the corticothalamic feedback, together with GABA_B-mediated inhibition in the thalamus, can account for many features of spike-and-wave oscillations, even when the thalamus is intact. These models generate detailed predictions that can be experimentally tested.

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