Investigating Language with Functional Neuroimaging

This chapter discusses the merits and drawbacks of the cognitive subtraction paradigm and reviews the progress in several specific areas, including verbal working memory, phonological processing, the role of the inferior frontal gyrus in semantic processing, and category-related word retrieval.

Abstract

This chapter examines the application of functional neuroimaging to the study of the neural basis of language processing. It discusses the merits and drawbacks of the cognitive subtraction paradigm and reviews the progress in several specific areas, including verbal working memory, phonological processing, the role of the inferior frontal gyrus in semantic processing, and category-related word retrieval. The functional neuroimaging techniques permit repeated measurement of the physiological state of the normal brain in a single experimental session. In the case of positron emission tomography (PET), these measurements are typically made about 10 minutes apart and in functional magnetic resonance imaging, measurements can be made consecutively. The subtraction technique is operationalized as digital image subtraction, but its significance lies in the implicit assumption of cognitive subtraction, a conceptual approach rooted in psychological processing models, particularly serial processing models. The initial application of PET to cognitive processes used a hierarchical subtraction approach, in which a series of tasks that were conceived to differ from one another by the addition of a small number of additional processing steps were devised. The subtraction of one task from the next more complex task in the hierarchy is held to isolate the cognitive processes added by the second task. In neuroimaging studies, the neural correlates of these additional processes are indexed by changes in cerebral blood flow.