Individual Variability of the Human Cerebral Cortex Identified Using Intraoperative Mapping

Background Intraoperative functional cortical mapping using direct electrical stimulation may show a wider individual variability than suggested by noninvasive imaging data of healthy subjects. Methods We assessed intraoperative variability of the frontal eye fields and the speech arrest sites in adult patients who underwent awake craniotomy with direct electrostimulation for treatment of diffuse gliomas located within eloquent regions, and we compared findings with human cortical parcellation of the Human Connectome Project. Results The frontal eye fields were defined by intraoperative direct electrostimulations (14.3% of patients) projected on the superior subdivision of the premotor cortex covering the areas defined as frontal eye fields (parcel index 10), area 55b (parcel index 12), and premotor eye field (parcel index 11) and in the posterior part of the dorsolateral prefrontal cortex covering the areas defined as inferior 6–8 transitional area (parcel index 97), area 8Av (parcel index 67), and area 8C (parcel index 73). The speech arrest sites were defined by intraoperative direct electrostimulations (100% of patients) projected predominantly posteriorly to the inferior frontal gyrus in the inferior subdivision of the premotor cortex, that is, rostral area 6 (parcel index 78), ventral area 6 (parcel index 54), and area 43 (parcel index 99). Conclusions Intraoperative functional cortical mapping using direct electrostimulation highlights that actual individual variability is wider than suggested by analyses of healthy subjects and results in atypical patterns of functional organization and structural and functional changes of the human cerebral cortex under pathologic conditions.