Functional magnetic resonance adaptation in visual neuroscience.

Functional magnetic resonance imaging (fMRI) is a powerful non-invasive tool to investigate neuronal processing. In the last ten years a new methodological approach in the field of fMRI has been developed: fMRI adaptation. It has been found that the repetition of a stimulus leads to a decrease of the fMRI signal in the brain region that processes this stimulus. The phenomenon has been related to neuronal adaptation effects found in single-cell recordings. Since the first experiments that observed fMRI-adaptation effects, the method has been applied extensively to study various visual phenomena, such as the perception of motion, shape, objects, and orientation. The great advantage of fMRI adaptation is that it allows assessing the functional response profile of a brain region at a subvoxel level. The purpose of the current review is to evaluate the different experimental approaches used to elicit fMRI-adaptation effects. We discuss papers published in the domain of visual neuroscience that made use of fMRI-adaptation paradigms. In doing so, we focus on methodological considerations concerning experimental design, stimulus presentation and influencing factors such as awareness and attention. In the course of this review, we show that different fMRI-adaptation designs capture heterogeneous neuronal adaptation effects. As the picture of the mechanisms underlying neuronal adaptation changes from simple synaptic fatigue to complex network interactions, the concept of fMRI adaptation has to be redefined.