Functional localization
Brief description of the functional localization approach
Previous research has implicated a number of brain regions in linguistic processing, but precise functional characterization of these regions has proven challenging. Limitations of traditional brain imaging 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 neural architecture in general, as opposed to some idiosyncratic properties of an individual brain. However, because brains differ across individuals in terms of size, shape, folding patterns, and the locations of functional areas relative to the sulci and gyri, activations often do not line up well across brains. This poor alignment leads to a loss of sensitivity and functional resolution, and makes it difficult to compare results across studies. 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 individual brain, a method that has been highly successful in the study of visual cortex but that has rarely been applied to neuroimaging studies of language prior to ~2010. This method enables pooling of data from corresponding functional regions across participants, rather than from corresponding locations in stereotaxic space (which may differ functionally because of the inter-subject anatomical variability).
Around 2005-2006, we began developing tools to define language-sensitive regions in individual subjects. We successfully developed a language “localizer” paradigm that quickly and reliably identifies brain regions previously implicated in linguistic processing, including the "classic" regions in the left inferior frontal and posterior temporal cortices (Fedorenko et al., 2010 J Neurophys).
The ability to define language-sensitive regions in individual participants opened the door to characterizing these regions in detail—as our group has been and continues to do—which is essential for developing models of language function in the brain and linking those models to existing cognitive and computational models.
(For the application of the methods described here to the ventral visual regions, see here.)
FAQ
How do functional localizers work?
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What are the advantages of functional localizers over traditional group-averaging methods?
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