Absence epilepsy is believed to be highly associated with the abnormal interactions between the cerebral cortex and thalamus.Besides the direct coupling,anatomical evidence indicates that the cerebral cortex and thalamus also communicate indirectly through an important intermediate bridge--basal ganglia.It has been thus postulated that the basal ganglia might play key roles in the modulation of absence seizures,but the relevant biophysical mechanisms still not be completely established.Using a computational model (see Figure 1),we demonstrate here that the typical absence seizure activities can be controlled and modulated by the direct GABAergic projections from the substantia nigra pars reticulata (SNr) to either the thalamic reticular nucleus (TRN) or the specific relay nuclei (SRN) of thalamus,through different biophysical mechanisms.Under certain conditions,these two types of seizure control are observed to coexist in the same network.More importantly,due to the competition between the inhibitory SNr-TRN and SNr-SRN pathways,we find that both decreasing and increasing the activation of SNr neurons from the normal level may considerably suppress the generation of typical 2-4 Hz spike-and-slow wave discharges in the coexistence region (see Figure 2).Taken together,these results highlight the bidirectional functional roles of basal ganglia in controlling and modulating absence seizures,and might provide novel insights into the therapeutic treatments of this brain disorder.