Functional localization in fMRI studies of language

Brief description: This website is dedicated to functional localization in fMRI studies of language. Here you can find information about the method, links to some relevant papers, as well as tools for download.

Acknowledgment: Much of this work was suported by Grant HD 057522 from Eunice Kennedy Shriver National Institute Of Child Health & Human Development awarded to Ev Fedorenko.

For the application of the methods described here to the ventral visual regions, see http://web.mit.edu/bcs/nklab/GSS.shtml.

The research program

Previous research has identified a number of brain regions that are engaged during linguistic processing, but precise functional characterization of these regions has proven challenging. Limitations of the current methods may be at least partly responsible.

In particular, in the traditional fMRI methodology individual brains are aligned together in a common space in order to determine whether activation patterns are similar across individuals and thus reflect something about human cognitive architecture in general, as opposed to some idiosyncractic properties of an individual brain. However, because brains differ across individuals in terms of size, shape, folding patterns and the locations of areas with particular cell types relative to the sulci and gyri, activations often do not line up well across brains. This poor alignment leads to a loss of sensitivitiy and functional resolution, and makes it difficult to compare results across studies (read more about the issues inherent in traditional group-based methods here). These problems have plausibly slowed down progress in the field of language research.

A clearer picture of the functional architecture of language may emerge if candidate language-sensitive regions are identified functionally within each subject individually, a method that has been highly successful in the study of visual cortex but that has rarely been applied to neuroimaging studies of language. This method enables pooling of data from corresponding functional regions across subjects, rather than from corresponding locations in stereotaxic space (which may differ functionally because of the inter-subject anatomical variability).

Around 2005-2006, I began developing tools to define language-sensitive regions in individual subjects. We successfully developed a language "localizer" which quickly and reliably identifies brain regions previously implicated in linguistic processing, including the "classical" regions in the left inferior frontal and posterior temporal cortices. These regions (i) are present in the vast majority of subjects individually, (ii) are replicable within subjects (both within and across scanning sessions) and have clear correspondence across subjects, and (iii) respond similarly to linguistic stimuli presented visually vs. auditorily. Furthermore, this localizer is robust to changes in task (e.g., passive reading vs. reading with a memory probe), materials, and various aspects of the design/procedure.

The ability to define language-sensitive regions in individual subjects opens the door to characterizing each core language-responsive region as well as the language system as a whole, which is essential for developing models of language function in the brain and linking those models to existing cognitive models.

The goal of this website is to share the tools that we have developed – and are continuing to develop – with the scientific and clinical communities, so that anyone who is interested in using this approach can easily do so. (If you are interested in what we have learned about the functional architecture of the language system using these methods, please go here.)