P04.11 Effect of hemisphere and tumor grade on default mode deactivation in glioma patients

Abstract

INTRODUCTION: In healthy subjects, the brain not only activates a network of brain areas during performance of a cognitive task, but also deactivates specific regions. The latter is known as the default mode network (DMN). It is hypothesized in the literature that within the DMN, deactivation in the extended posterior cingulate cortex region (ePCC) is associated with external focus and alertness. In this study, we analyzed data from a database of patients with a low grade (LGG) or high grade glioma (HGG). All patients performed a language production task which was part of a clinical fMRI protocol. For language production tasks, deactivation in the DMN appears to be lateralized to the right hemisphere, in contrast to the activation which is generally lateralized to the left. We were interested whether hemispheric location and tumor grade would differentially affect the capacity to deactivate the ePCC. METHODS. Our database (30 HGG patients with tumor in left hemisphere, average age 50,.5; 26 HGG, right, age 50,7; 37 LGG, left, age 37.6; 16 LGG right, age 36.5). All patients performed a verb generation fMRI protocol, prior to surgery. For each group, we calculated the average signal difference in the ePCC brain region, a-priori based on an anatomical atlas. Group means were compared using unpaired tests. RESULTS: Results indicated that patients with a HGG in the right hemisphere showed significantly less deactivation in ePCC than patients with a HGG in the left hemisphere (t = 2.23, p = 0.03) or patients with a LGG in the left hemisphere (t = 2.00; p = 0.05), while the difference with patients with a LGG in the right hemisphere showed a trend (t = 1.80, p = = 0.08). In patients with a LGG, the hemisphere of the tumor did not have an effect on deactivation of the ePCC (t = 0.38; p = 0.70). CONCLUSION: Our study indicates that within the four groups of patients, those with a HGG in the right hemisphere showed the most impaired capacity to deactivate the ePCC during a cognitive task. It is known from healthy subjects that deactivation during a language production task tends to be right lateralized, and this may explain that this effect is less pronounced when the tumor is in the left hemisphere. The reduced capacity to inhibit ePCC in patients with a HGG may be associated with reduced alertness and capacity to focus.