Effects of Radiotherapy on the Executive Functions Network: fMRI Connectivity in Patients with Lateralized Mediobasal Temporal Lesions

Published data show that the positive effect of radiotherapy (RT) for brain tumors can be accompanied by adverse sequelae in the form of the development of neurocognitive deficit due to the side effects of radiation on critical brain structures. In addition, there are indications that hippocampal neurogenesis may be modulated, with subsequent activation of a number of cognitive functions. Executive functions (EF), including the initiation, planning, regulation, and monitoring of any purposeful activity, constitute an important component of human cognitive activity. The structural and functional support of these functions is currently associated with the prefrontal and parietal areas of the hemispheres, as well as formations in the inferior temporal cortex and hippocampus. The aim of the present work was to produce a dynamic assessment of the state of the EF network by analysis of resting fMRI connectivity before and six months after RT. Fourteen patients with lateralized tumor lesions of the mediobasal parts of the temporal lobe were followed: seven with left-sided lesions and seven with right-sided lesions. The control group consisted of nine healthy subjects. Each subject underwent fMRI in the resting state, followed by analysis of functional connectivity between specified regions of interest corresponding to the topography of the EF network. The results were compared with MRI tumor morphometry data. On the background of decreases in tumor volume or stabilization of tumor growth, functional effects at six months post-RT were found to differ and to depend on lesion lateralization: there was a tendency to normalization with right-sided lesions, while left-sided lesions produced increases in functional sequelae.