Activity in the paracingulate and cingulate sulci during word generation: An fMRI study of functional anatomy

The supracallosal medial frontal cortex can be divided into three functiona l domains: a ventral region with connections to the limbic system, an anter ior dorsal region with connections to lateral prefrontal systems, and a pos terior dorsal region with connections to lateral motor systems. Lesion and functional imaging studies implicate this medial frontal cortex in speech a nd language generation. The current functional magnetic resonance imaging ( fMRI) study of word generation was designed to determine which of these thr ee functional domains was substantially involved by mapping individual subj ects' functional activity onto structural images of their left medial front al cortex. Of 28 neurologically normal right-handed participants, 21 demons trated a prominent paracingu- late sulcus (PCS), which lies in the anterior dorsal region with connections to lateral prefrontal systems. Activity inc reases for word generation centered in the PCS in 18 of these 21 cases. The posterior dorsal region also demonstrated significant activity in a majori ty of participants (16/28 cases). Activity rarely extended into the cingula te sulcus (CS) (3/21 cases) when there was a prominent PCS. If there was no prominent PCS, however, activity did extend into the CS (6/7 cases). In no case was activity present on the crest of the cingulate gyrus, which is he avily connected to the limbic system. Thus, current findings suggest that m edial frontal activity during word generation reflects cognitive and motor rather than limbic system participation. The current study demonstrates tha t suitably designed fMRI studies can be used to determine the functional si gnificance of anatomic variants in human cortex.