OBJECTIVE Epileptic networks are char-acterized as two states,seizures or more prolonged inter-ictal periods.However,cellular mechanisms underlying the contribution of interictal periods to ictal events remain unclear.METHODS Here,we present the procedure for labeling seizure-activated and interictal-activated neuro-nal ensembles in mouse hippocampal kindling model using an enhanced-synaptic-activity-responsive element.This technique is combined with genetically encoded effectors to characterize and manipulate neuronal ensembles recruited by focal seizures(FS-Ens)and interictal periods(IP-Ens)in piriform cortex,a region that plays a key role in seizure generation.RESULTS Ca2+ activities and histo-logical evidence reveal a disjointed correlation between the two ensembles during FS dynamics.Optogenetic acti-vation of FS-Ens promotes further seizure development,while IP-Ens protects against it.Interestingly,both ensem-bles are functionally involved in generalized seizures(GS)due to circuit rearrangement.IP-Ens bidirectionally modulates FS but not GS by controlling coherence with hippocampus.CONCLUSION This study indicates that the interictal state may represent a seizure-preventing environment,and the interictal-activated ensemble may serve as a potential therapeutic target for epilepsy.

OBJECTIVE Cognitive deficit is a com-mon comorbidity in temporal lobe epilepsy(TLE)and that is not well controlled by current therapeutics.Currently,how epileptic seizure affects cognitive performance remains largely unclear.The subiculum is the major out-put of the hippocampus,which projects to entorhinal cor-tex and other more distinct brain regions.Physiologically,the subiculum codes spatial working memory and naviga-tion information including place,speed,and trajectory.Importantly,prior studies have noted the importance of the subiculum in the beginning,spreading,and generaliz-ing process of hippocampal seizure.How seizure-activated neurons in subiculum participate in cognitive impairment remains largely elusive.METHODS In this study,we sought to label the subicular seizure-activated c-fos+ neu-rons with a special promoter with enhanced synaptic activity-responsive element E-SARE in the subiculum,combined with chemogenetics and designer receptors exclusively activated by designer drugs(DREADDs),Ca2+ fiber photometry approaches,and behavioral tasks,to reveal the role of these neurons in cognitive impairment in epilepsy.RESULTS We found that chemogenetic inhibi-tion of subicular seizure-tagged c-fos+ neurons(mainly CaMK Ⅱ α+ glutamatergic neurons)alleviates seizure generalization and improves cognitive performance in the hippocampal CA3 kindling TLE model.While inhibition of seizure-labeled c-fos+ GABAergic interneuron shows no effect on seizure and cognition.As a comparison,che-mogenetic inhibition of the whole subicular CaMK Ⅱ α+ neuron impairs cognitive function in na?ve mice in basal condition.Notably,inhibition of subicular seizure-tagged c-fos+ neurons enhances the recruitment of cognition-responsive c-fos+ neurons via increasing neural excitability during cognition tasks.CONCLUSION Our results dem-onstrate that subicular seizure-activated c-fos+ neurons contribute to cognitive impairment in TLE,suggesting sei-zure-tagged c-fos+ neurons as the potential therapeutic target to alleviate cognitive impairment in TLE.