Memories are evolving constructs prone to modifications. Here, we explore the temporal rules that determine whether memories are associated, by cooperation, or selected and lost, by competition. To tackle this question, we have built a conceptual model of the rules underlying synaptic cooperation and competition between the cortical and thalamic afferents to projection neurons of the lateral amygdala (LA), a circuit necessary for the formation of fear-conditioning memories. We found that heterosynaptic cooperation and competition between thalamic and cortical inputs to the LA follow a strict temporal rule in which the heterosynaptic maintenance of thalamic LTP is time-restricted by the presynaptic activation of endocannabinoid receptors. Striking, we found that events are associated following the same temporal rule described for heterosynaptic cooperative maintenance of thalamic and cortical synapses. Using a modified fear discrimination paradigm, we show that short time intervals between events lead to a cooperative fear expression that is modulated by thalamic activity. We also found that introducing a third event induces competition leading to the destabilization of the weaker trace. Interestingly, recall of a previously acquired memory also leads to the destabilization of the weak trace. Further, we found that modulation of the thalamic inputs to the amygdala, but not the cortical can later the time interval in which memories are associated. Our results show a key and undescribed temporal rule of memory association modulated by thalamic activity that shapes memory consolidation and reconsolidation.Acknowledgements: Project funded by FCT reference PTDC/MED-NEU/30772/2017 (LISBOA-01-0145-FEDER-030772) and FCT reference doi.org/10.54499/2022.09002.PTDC.