The term “nostalgia” was coined in the late 17th century by a Swiss physician named Johannes Hofer. He used the roots of two Greek words, “nostos” and “algos” — meaning “suffering” and “origins” — to describe what he thought was a neurological disorder affecting Swiss mercenaries. Although the clinical definition of nostalgia has evolved — it is now considered a psychological condition, and similar to melancholy — scientists agree it does have some neurological underpinnings.LeDoux suggests that although little is known about the neuroscience of nostalgia, it probably has something to do with how memory and emotions are stored in the brain. Short-term memories contain information such as the location of car keys or a clever twitter handle and are stored in the frontal lobe. But long-term memories — such as a friend’s name or how to ride a bike — are moved via neurotransmitters (through a process called “consolidation” that often happens during sleep) to the hippocampus, a part of the brain located deeper in the cranial cavity. Neuroscientists have traced memory to particular brain circuitry, showing how a stable long-term memory is formed through connections between nerve cells. But when a memory is stored at a time of emotional arousal, the imprint is more powerful, possibly due to the neurotransmitters — comparable to hormones in the endocrine system — that the brain secretes in that moment. LeDoux thinks that the process of forming the mental imprint of an event may be closely linked to what is known as “flashbulb memory.” This ultra-clear memory was first identified in 1977 by Roger Brown, professor at Harvard University, and his graduate student James Kulik, currently professor emeritus at the University of California, San Diego. In a telephone interview, Kulik says that at the time, people didn’t think of memory and emotions as closely linked. “Memory research involved primarily memory for words, syllables and other nonemotional stimuli that wasn’t personally meaningful. Roger and I were interested in how intensely personal memories are stored, so to have a common reference point for respondents, we focused on personal memories for public events.” Asking individuals to recall the assassination of John F. Kennedy, they discovered that these memories captured the event with such clarity and vividness that they thought it triggered a unique mechanism in the brain similar to taking a picture, hence the “flashbulb.” Kulik notes that in bringing the study of emotion and memory together, they helped launch the study of autobiographical memory and, more generally, the explosion of research on emotion, which continues to this day.