Lexical selection and the (pre)supplementary motor area white matter system

Abstract

The supplementary and pre-supplementary motor areas (SMA and pre-SMA) has been suggested as involved in language processing since the early ages of electrical stimulation mapping. However they received far less attention in this sense than the classic, perisylvian areas. Recent updates in the neuroanatomy allowed to revisit the (pre)SMA showing its abundant white matter connections towards inferior and middle frontal gyri (MFG, IFG) as well as to the caudate nuclei. Additionally, observations in people with brain lesions suggested the role of these connections in language processing (speech motor control, sentence completion or verb generation/lexical selection). However the up-to-date reports lack the anatomical precision in joining language production to specific projections. To address this gap of knowledge, we will compare the microstructural properties of the three projections stemming from the (pre)SMA hub (IFG, MFG and caudate; left and right) with individual performance in the verb generation (VG) task. In this sense, we will analyze an existing dataset of high-resolution diffusion-weighted imaging (DWI) of 50 healthy subjects and their results in VG. The task consisted of 100 high-frequency concrete Dutch nouns (e.g.“hond” [dog]), where the possible noun-to-verb pairs did not share the morphological stem. All the items were sorted into high (<mean of the number of response options given) and low semantic selection conditions (>mean). We expect that the microstructural properties of the connections towards IFG will explain the variability of the VG task (more robust for the high selection condition) and that these effects will be left-lateralized. With respect to the connections towards caudate nucleus and MFG, we expect similar effect with regard to the high selection condition, but we do not assume that these effects will be lateralized towards left. These results will be the first to show similar relationships in healthy population.