In the recent decades structural connectivity between Broca's area and the basal ganglia has been postulated in the literature, though no direct evidence of this connectivity has yet been presented. The current study investigates this connectivity using a novel diffusion-weighted imaging DWI fiber tracking method in humans in vivo. Our findings suggest direct connections between sub-regions of Broca's area and the anterior one-third of the putamen, as well as the ventral anterior nucleus of the thalamus.
Thus, we are the first to provide a detailed account of inferred circuitry involving basal ganglia, thalamus, and Broca's area, which would be a prerequisite to substantiate their support of language processing. Language is a complex cognitive skill essential to many aspects of our everyday lives. Much effort has been dedicated to investigating the role and function of cortical substrates involved in language processing, most notably dominant hemisphere perisylvian cortex.
Such work started over a century ago with luminaries such as Broca and Wernicke and has continued into the present Broca, ; Wernicke, However, in recent decades evidence from lesion, neuropsychological, and neuroimaging studies suggests that the basal ganglia support language processing Crosson, ; Copland et al. In particular, basal ganglia have been implicated to play a role in lexical selection and retrieval, various aspects of syntactic, morphological, and phonological processing, as well as higher-order language processing Ullman, , ; Friederici, Many of these functions also are commonly attributed to Broca's area Amunts et al.
Based on this relationship, a number of papers have postulated the existence of Broca's area basal ganglia thalamocortical circuitry Brunner et al. It is believed that this circuitry should closely resemble structural organization of other presently known prefrontal cortex basal ganglia loops Alexander et al.
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Projections from Broca's area should enter the input nuclei of the basal ganglia circuitry, the caudate or the putamen, thence projecting to the globuspallidus and substantianigra.
