Objective. Although the role of the fronto-parietal network in spatial working memory (spatial WM) has been indicated, few reports have validated the existence of the fronto-parietal network in the post-mortem human brain, and no direct evidence supporting the role of the network in spatial WM has been presented in living human brain. In this study, we validated the existence of the network, in particular the superior longitudinal fasciculus (SLF) I in postmortem human brains, and examined how the SLF I processes spatial WM in patients with prefrontal glioma.
Methods. Three formalin-fixed cerebral hemispheres were dissected to reveal the association fibers between superior frontal gyrus (SFG) and parietal lobe (PL) with a Klingler's method. Four patients with right prefrontal glioma underwent resection under local anesthesia. The status of spatial WM and SLF I were evaluated pre-, and postoperatively with a spatial 2-back task and diffusion tensor imaging (DTI)-tractography, respectively. In addition, intraoperative spatial 2-back task was performed and we evaluated the response under direct subcortical electrical stimulation (DES).
Results. The fiber tract between the SFG and PL corresponding to the SLF I could be identified in all three hemispheres. In all four patients, the right SLF I could be visualized with preoperative DTI-tractography. Three patients had difficulties in providing correct responses in spatial 2-back task intraoperatively with DES close to the SLF I. While two patients with postoperative verified SLF I had preserved spatial WM, the other two patients for whom we were unable to visualize the SLF I had worsened spatial WM.
Conclusions. The existence of the association fiber tract, i.e., SLF I, was validated in post-mortem human brains. Further, we demonstrate, in the living human brain, that the right SLF I could subserve spatial WM.