Event-related fMRI in cognition.

A primary advantage of functional magnetic resonance imaging (fMRI) over other techniques in neuroscience is its flexibility. Researchers have used fMRI to study a remarkable diversity of topics, from basic processes of perception and memory, to the complex mechanisms of economic decision making and moral cognition. The chief contributor to this experimental flexibility-indeed, to the growth of fMRI itself-has been the development of event-related experimental designs and associated analyses. The core idea of an event-related design, as first articulated in the late 1990s, is the separation of cognitive processes into discrete points in time (i.e., "events") allowing differentiation of their associated fMRI signals. By modeling brain function as a series of transient changes, rather than as an ongoing state, event-related fMRI allowed researchers to create much more complex paradigms and more dynamic analysis methods. Yet, this flexibility came with a cost. As the complexity of experimental designs increased, fMRI analyses became increasingly abstracted from the original data, which in turn has had consequences both positive (e.g., greater use of model-based fMRI) and negative (e.g., fewer articles plot the timing of activation). And, as event-related methods have become ubiquitous, they no longer represent a distinct category of fMRI research. In a real sense, event-related fMRI has now become, simply, fMRI.