INTRODUCTION: Beyond motor functions of the primary motor cortex, the secondary motor areas that lie in the medial and lateral frontal regions play important roles in motor and speech executions as a part of negative motor networks interconnected by cortico-striatal (subcallosal fascicle, SCF) and cortico-cortical (frontal aslant tract, FAT) pathways; however, the neurophysiological mechanisms governing the networks remain unclear.
METHODS: To elucidate the functions associated with these tracts and influence to maximal surgical resection, we retrospectively selected 19 frontal glioma patients with awake surgery, and evaluated the relationship between these subcortical tracts and postoperative disorder of speech and motor initiations by verbal fluency test and tract-specific measurements in probabilistic tractography determined by three regions of interest (pre-supplementary motor area, pars opercularis and caudate nucleus).
RESULTS: All patients except for one experienced intraoperative inhibition of speech and/or movement by direct electric sub-cortical stimulations on the surgical boundaries. In tractography, the subcortical distributions of stimulated sites were corresponding to the running of these tracts in bilateral hemispheres. There were significant correlations between postoperative deterioration of verbal fluency and surgical resection close to these tracts. A surgical resection close to left FAT or bilateral SCF transiently could result in postoperative disorders of speech initiation (p=0.003) or motor initiation (p=0.026), respectively.
CONCLUSION: FAT and SCF would cooperatively play roles in verbal fluency and self-initiated speech and motor actions, as a part of modulatory networks with basal ganglia complex. The posterior boundaries of operative resection of frontal gliomas should be determined just in front of these cortico-subcortical pathways, which could be detected by intraoperative direct electric stimulation mappings, for goals of postoperative rapid improvement and good outcomes in executive functions.