Network-level causal analysis of set-shifting during trail making test part B: A multimodal analysis of a glioma surgery case.

The trail making test part B (TMT-B) is one of the most widely used task for the assessment of set-shifting ability in patients. However, the set of brain regions impacting TMT-B performance when lesioned is still poorly known. In this case report, we provide a multimodal analysis of a patient operated on while awake for a diffuse low-grade glioma located in the right supramarginal gyrus. TMT-B performance was probed intraoperatively. Direct electrical stimulation of the white matter in the depth of the resection generated shifting errors. Using the recent methodology of axono-cortical-evoked potentials (ACEP), we demonstrated that the eloquent fibers were connected to the posterior end of the middle temporal gyrus (MTG). This was further confirmed by a tractography analysis of the postoperative diffusion MRI. Finally, the functional connectivity maps of this MTG seed were assessed in both pre- and post-operative resting state MRI. These maps matched with the Control network B (13th) and Default B (17th) from the 17-networks parcellation of (Yeo et al., 2011). Last but not least, we showed that the dorsal attention B (6th), the control A & B networks (12th and 13th) and the default A (16th) have been preserved here but disconnected after a more extensive resection in a previous glioma case within the same area, and in whom TMT-B was definitively impaired. Taken together, these data support the need of a network-level approach to identify the neural basis of the TMT-B and point to the Control network B as playing an important role in set-shifting.