Expressive writing is a form of writing therapy developed primarily by James W. Pennebaker in the late 1980s. The seminal expressive writing study instructed participants in the experimental group to write about a 'past trauma', expressing their very deepest thoughts and feelings surrounding it. In contrast, control participants were asked to write as objectively and factually as possible about neutral topics (e.g. a particular room or their plans for the day), without revealing their emotions or opinions. For both groups, the timescale was 15 minutes of continuous writing repeated over four consecutive days. It was also instructed that should a participant run out of things to write, they should go back to the beginning and repeat themselves, perhaps writing a little differently.