Researchers at The Hospital for Sick Children in Toronto have made a breakthrough in understanding the inner workings of this phenomenon. By studying the brains of mice, they found that stress causes the release of endocannabinoids — chemicals that normally help us form specific, contextual memories. However, in high amounts, these endocannabinoids disrupt the brain’s “gatekeeper” neurons, leading to the formation of overly large, generalized memory engrams.