Insight problem solving is characterized by mental impasses,states of mind in which the problem solver does not know what to do next.Although many studies have investigated the neural correlates of insight problem solving,however,the question when mental impasses occur during insight problem solving has been rarely studied.The present study adopted high temporal resolution ERPs to investigate the temporal dynamics of an impasse underlying insight problem solving.Time locked ERPs were recorded associated with problems with impasses(PWI) and problems without impasses(POI).The problem types were determined by participants’ subjective responses.The results revealed an early frontocentral P2 was linked with the preconscious awareness of mental impasses and a P3a was associated with fixed attention when the impasse formed.These findings suggest the impasse may occur initially at a relatively early stage and metacognition plays an important role in insight problem solving. Insight problem is characterized by mental impasses, states of mind in which the problem solver does not know what to do next. Many many studies have investigated the neural correlates of insight problem solving, however, the question when mental impasses occur during insight problem solving has been rarely studied. The present study adopted high temporal resolution ERPs to investigate the temporal dynamics of an impasse underlying insight problem solving.Time locked ERPs were recorded associated with problems with impasses (PWI) and problems without impasses (POI). The problem types were determined by participants’ subjective responses. The results revealed an early frontocentral P2 was linked with the preconscious awareness of mental impasses and a P3a was associated with fixed attention when the impasse formed. these findings suggest the impasse may occur initially at a relatively early stage and metacognition plays an important role in insight problem solving.