Abstract
Background
Language production is usually fast, precise and effortless. However, in some cases, for instance if we experience difficulty finding a word automatically, language production becomes a more difficult cognitive task. Functional MRI studies have shown that execution of a more difficult word search task such as the widely applied verb-generation task is associated with left lateralized activation of a fronto-temporal network (‘FTN’). It is however also associated with right lateralized inhibition of a network called the ‘default mode network’ (‘DMN’). The precise function of the DMN is still largely unknown, but recent studies have suggested that inhibition does facilitate cognitive task execution. In this study we examined a large set of clinical functional MRI scans measuring activation patterns associated with verb generation in patients with a low or high grade glioma. Results were also compared to those of healthy controls. We specifically looked at the level of activation in the FTN and DMN.
Material and Methods
This study used presurgical fMRI data of patients with a low-grade (‘LGG’: N= 96) or high grade glioma (‘HGG’: N = 110), as well as healthy controls (‘HC’: N = 16). FMRI scans were produced using a 3T Philips scanner (PRESTO pulse sequence, voxel-size: 4x4x4 mm, TE: 1.5 sec). Scans were corrected for movement and analysed. Individual activation maps were spatially normalized to MNI space. The average signal change during a covert verb generation task was calculated using cube-shaped ROIs (15mm3) over important regions of the FTN and DMN. Signal changes were averaged over all ROIs for each network. A multivariate analysis was performed to examine differences in network activation between the three groups. Follow-up univariate tests were performed for each group and network.
Results
Statistical analyses revealed a significant network by group interaction (F(2,219) = 5.70, p = 0.004). Follow-up analysis revealed that this interaction reflected less deactivation of the DMN in both LGG (F(1,110) = 4.43, p = 0.04) and HGG patients (F(1,124) = 8.00; p = 0.005) compared to HC. Activation in the FTN did not differ significantly between groups (LGG: F(1,110) = 0.006; p = 0.94; HGG(1,124): F = 0.20, p = 0.66).
Conclusion
Patients with a glioma show less inhibition of the DMN during word search tasks then healthy subjects, independent of the grade of the glioma. It is hypothesized that inhibition of the DMN can facilitate cognitive task execution. Our results add new knowledge that may help in the understanding of deficits in language production as well as related cognitive tasks