Some types of epileptic seizures involve both thalamus and cerebral cortex,
while other types can be evoked in the cerebral cortex without thalamic
participation. We investigated the possible role of low-threshold spike (LTS)
cortical neurons in the genesis of these intracortical seizures. We found LTS
cortical neurons in cat area 5-7 in vivo, which properties could be
modeled based on relatively weak densities of the T-type calcium channel. At
the network level, a small minority of LTS pyramidal cells was sufficient to
generate paroxysmal oscillations with spike-and-wave (SW) field potentials.
These oscillations reproduce the properties of intracortical SW paroxysms
observed in athalamic cats, such as the slow frequency (1.8-2.5 Hz). We
suggest that calcium-mediated rebound mechanisms intrinsic to cerebral cortex
can explain the genesis of intracortical SW activity.
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