Sulcal depth is correlated with phonological encoding during language processing in Broca's Area.

BACKGROUND: Language relies on a left-lateralized fronto-temporal network whose functional organization likely reflects structural factors that emerge early in neurodevelopment. One such factor is sulcal depth, which has been proposed as a key anatomical marker of functional specialization. Here, we investigated potential structure-function relationships with respect to phonological encoding, a core linguistic process linking lexical representations and articulatory planning.

METHODS: Thirty-two healthy adults performed a rhyming judgment task, known to be sensitive to phonological coding, during fMRI. Activation during task performance was related to cortical morphology derived from structural MRI in the same subjects, focusing on sulcal depth and other standard measures (i.e. cortical volume, surface area and thickness).

RESULTS: Rhyming task performance elicited predominantely left-lateralized activation in the inferior frontal cortex and other regions including the precentral, postcentral, supramarginal, and superior temporal cortex, as well as the supplementary motor area, the middle cingulate and calcarine cortex, the left cerebellum and the basal ganglia. A cluster in the left inferior frontal gyrus (pars opercularis, a subregion of Broca's area) showed a significant association between sulcal depth and activation during the rhyming task. No associations were observed for other regions or for other structural measures.

DISCUSSION: These findings raise the possibility that phonological encoding may have an origin in early-emerging cortical folding patterns and support the view that core language functions are scaffolded by genetically driven neurodevelopmental processes.