Anthony Stigliani

Repetition of a stimulus typically leads to a reduction in neural response. This adaptation effect, sometimes known as repetition suppression or neural priming, can be observed both in individual neurons (as illustrated by a reduction in firing rate) and fMRI voxels containing hundreds of thousands of neurons (as illustrated by a reduction in BOLD response). When measured with fMRI, this repetition-related reduction in neural activity is known as fMRI-Adaptation (fMRI-A) and can be used to make inferences about the nature of neuron representations and their sensitivity to various stimulus transformations (e.g., Grill-Spector et al. 1999). While fMRI-A has proven to be a powerful and flexible tool for studying a variety of topics, some experimental designs are more optimal for studying particular phenomena than others. The purpose of this wiki page is to outline the critical components of fMRI-A methods and describe different types of experimental designs that may be used.

Background

Response of an example IT neuron to first the presentation of stimulus A (left), the first presentation of stimulus B (center), and repeated presentation of stimulus A (right) (courtesy of Grill-Spector et al. 2006).

Reductions in neural firing related to stimulus repetition were first observed in electrophysiological recordings of neurons in macaque inferior temporal (IT) cortex when visual stimuli were repeated. Instead of representing a general reduction in neural response when two stimuli are shown in quick succession, response attenuation is only observed when the same item is repeated. This raises the questions of what constitutes a an item, but how one chooses to define an individual stimulus or item depends on the specificity of the representations of interest. In the domain of visual object recognition, items are typically construed as specific object exemplars or faces (e.g., your desk or mother's face), but repetition-related reductions in neural response have also been observed when different objects belonging to the same category are presented sequentially (Vuilleumier et al. 2002).

References

Grill-Spector, K., Henson, R., & Martin, A. (2006). Repetition and the brain: neural models of stimulus-specific effects. Trends in Cognitive Science, 10(1), 14-23.
Vuilleumier, P., Henson, R.N., Driver, J., & Dolan, R.J. (2002). Multiple levels of visual object constancy revealed by event-related fMRI of repetition priming. Nature Neuroscience, 5(2), 491-499.