Neural mechanisms of lexical selection
When speaking, we are able to access thousands of words in our mental lexicon and pick the specific word labelling the intended concept in less than a second. In psycholinguistics, this process if referred to as lexical selection. Clinical and functional neuroimaging evidence suggests that lexical selection heavily relies on the left inferior frontal gyrus (IFG). However, another series of studies implicate a different neuroanatomical structure – the left supplementary motor complex (SMC) – in the same process. In this project, we aim to investigate how these two areas interact to subserve lexical selection.
At the first stage of the project, we tested whether a disruption of connectivity between the IFG and the SMC following stroke is associated with a lexical selection deficit. Using diffusion-tensor imaging, we reconstructed the left frontal aslant tract (FAT; a white-matter pathway that connects the IFG and the SMC) in 20 patients who suffered a stroke. We then related the metrics of the frontal aslant tract integrity to the measures of lexical selection abilities of these patients. We replicated the previous finding that the IFG damage causes a lexical selection deficit. However, we did not observe a robust relation between the FAT volume and lexical selection measures. We speculate that disruption of the FAT may have caused a lexical selection deficit early post-stroke, followed by successful recovery prior to the behavioral assessment. This suggests that the network subserving lexical selection may undergo successful functional reorganization over the course of post-stroke recovery.
At the next stage, we aim to address the neurophysiological interactions between the IFG and the SMC during lexical selection. First, this will resolve the question whether the IFG-SMC connectivity underlies lexical selection in healthy individuals. Second, fine temporal resolution of the neurophysiological methods offers an opportunity to elucidate the dynamics of the IFG-SMC interactions during lexical selection on the millisecond timescale. Finally, revealing the neurophysiological correlates of lexical selection will pave the way for further longitudinal studies addressing the reorganization of lexical selection over the course of recovery following focal brain lesions.
Zyryanov, A., Malyutina, S., & Dragoy, O. (2020). The left frontal aslant tract and lexical selection: Evidence from frontal lobe lesions. Neuropsychologia. Advance online publication. doi:10.1016/j.neuropsychologia.2020.107385
The study was supported by the RF Government Grant, ag. No. 14.641.31.0004.
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