How do we remember a phone number we were just about to call? How do we memorize the contents of a lecture or a movie? Already Plato and Aristotle asked how memory is stored as changes in the brain. In a new study, Professor Peter Jonas and his group at the Institute of Science and Technology Austria (IST Austria), including first author David Vandael, found that short-term memory may be formed by storing vesicles of neurotransmitter. These vesicle pools could be an “engram,” a physical trace of memory. The study is published in the journal Neuron.