Task-demand modulation of activation in Broca’s area

A number of brain imaging studies of sentence comprehension have reported evidence of activation in Broca’s area correlated with the processing of syntactically complex sentential material in both FMRI and PET studies (e.g., Caplan, 1995). This finding fits well with several decades of evidence concerning the effects of lesions on Broca’s area. Independent FMRI and PET investigations of working verbal memory (WVM) (e.g., Smith & Jonides, 1999) have also found evidence of activation of Broca’s area correlated with increased memory load. One hypothesis to consider based on these two pieces of evidence is that Broca’s area is involved in verbal working memory operations, and that complex structural processing employs this same resource. However, the experimental evidence does not easily recon-cile with such a hypothesis. There is, for example, evidence suggesting that individuals with working memory deficits caused by brain lesions have no significant language processing difficulties, and, simulta