Figure 1. Hemodynamic responses measured within the first study using an event-related fMRI design.
In this very early study, participants viewed simple visual stimuli that flashed for one second and then turned off for a long duration. These short stimuli evoked a detectible increase in the measured fMRI signal, now known as the BOLD hemodynamic response. Data from Blamire and colleagues (1992); figure from Huettel and colleagues (2009).