Phonetic Encoding, Verbal Working Memory and the Role of Brocas Area (PhD)

Even though Broca’s area has been associated with speech and articulation since the 19th century, the exact role that it plays is still a matter of debate. Recent models on the neuroanatomy of language have assigned Brocas area to different processes: syllabification (Indefrey and Levelt 2004), articulatory code storage (Hickok and Poeppel 2004) and verbal working memory (Chein and Fiez 2001; Chein et al. 2002). The subject of this doctoral dissertation is to examine phonetic encoding and disambiguate the role of Broca’s area. This issue was addressed in a series of functional magnetic resonance imaging studies (fMRI) involving speech production, where the phonological properties of pseudowords were manipulated in a way that differentiated between syllabification and articulatory code generation. The load on verbal working memory was also changed. The behaviour of Broca’s area was then examined in response to these manipulations to determine the dependence of the observed results on the different levels of processing and verbal working memory.
The results from the present studies suggest that the dorsal premotor cortex has a consistent role in articulatory code generation, irrespective of verbal working memory demands. In contrast, Broca’s area, specifically Brodmann area 44 (BA44), showed a main effect of phonetic encoding only during delayed response trials. Interestingly, area BA44 was also found to be functionally segregated between the dorsal and ventral part. The dorsal part was sensitive to articulatory and phonological load, such as stimulus length. The ventral part, on the other hand, was sensitive to sublexical stimulus properties, but only during delayed response trials. These findings suggest that BA44 is not a homogenous region, but it is divided into a dorsal premotor and a ventral prefrontal part. These results add another dimension of complexity to the study of Broca’s area, its functional segregation, and its role in language production.

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Related Publications and Presentations

  • Marina Papoutsi, J.A. de Zwart, J.M. Jansma, Martin Pickering, James A. Bednar, and B. Horowitz, “The Processing of low frequency pseudowords by Broca’s area”, Organisation for Human Brain Mapping, 13th Annual Meeting, Chicago, USA, 2007.
  • Marina Papoutsi, “The Functional Anatomy of Broca’s area”, Dr B. Horwitz’s Lab. Brain Imaging and Modelling section, NIDCD, NIH, USA, 2006.
  • Marina Papoutsi, and Ian Marshall, “Re-evaluating Magnetic Source MRI”, Organisation for Human Brain Mapping, 12th Annual meeting, Florence, Italy, 2006.

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