Sequential Roles of Primary Somatosensory Cortex and Posterior Parietal Cortex in Tactile-visual Cross-modal Working Memory: A Single-pulse Transcranial Magnetic Stimulation (spTMS) Study

• In this study, we found the causal evidence linking primary somatosensory cortex (SI) activity with behavioral performance in tactile-visual cross-modal associations.
• Our results indicate that SI, in addition to posteior parietal cortex (PPC), plays an essential role in sequential neural processes of cross-modal associations and working memory.

BackgroundBoth monkey neurophysiological and human EEG studies have shown that association cortices, as well as primary sensory cortical areas, play an essential role in sequential neural processes underlying cross-modal working memory.ObjectiveThe present study aims to further examine causal and sequential roles of the primary sensory cortex and association cortex in cross-modal working memory.MethodsIndividual MRI-based single-pulse transcranial magnetic stimulation (spTMS) was applied to bilateral primary somatosensory cortices (SI) and the contralateral posterior parietal cortex (PPC), while participants were performing a tactile-visual cross-modal delayed matching-to-sample task. Time points of spTMS were 300 ms, 600 ms, 900 ms after the onset of the tactile sample stimulus in the task.ResultsThe accuracy of task performance and reaction time were significantly impaired when spTMS was applied to the contralateral SI at 300 ms. Significant impairment on performance accuracy was also observed when the contralateral PPC was stimulated at 600 ms.ConclusionSI and PPC play sequential and distinct roles in neural processes of cross-modal associations and working memory.