Task demand modulates somatosensory-frontoparietal networks during delay and retrieval periods in tactile working memory

The primary somatosensory cortex (SI) is traditionally regarded as a sensory encoding region, yet growing evidence implicates it may also work in the maintenance and manipulation of tactile working memory (TWM), and interact with frontoparietal (FP) pathway under varying task demands. Here, we use high-field fMRI and a custom pneumatic tactile stimulation device to examine neural dynamics across distinct WM phases during a retro-cue task. We manipulate task demand during the delay phase (complex/simple retro-cues) and the retrieval phase (recall/non-recall) while isolating encoding, delay, and retrieval phases. Functional connectivity results reveal increased functional coupling between SI and FP regions as task demand increases. Moreover, effective connectivity results show the high-demand task selectively modulates excitatory connections from the posterior parietal cortex (PPC) to SI during maintenance, and from PPC to dorsolateral prefrontal cortex (dlPFC) as well as from dlPFC to SI during manipulation. These results demonstrate that SI engages in demand-dependent excitatory interactions with FP regions, supporting its central role throughout the whole TWM process.