The long-term impact of irradiation on functional connectivity in brain circuits involved in memory processes after pediatric posterior fossa tumor.

PURPOSE: Memory is one of the main specific cognitive domains impaired with attention and processing speed after a pediatric brain tumor. This work explored the long-term impact of radiotherapy in children with posterior fossa tumor (PFT) on brain connectivity in neural circuits involved in memory using resting-state functional magnetic resonance imaging (rs-fMRI). METHODS: A total of 20 irradiated and 15 non-irradiated PFT survivors, and 21 healthy controls, prospectively included in the IMPALA study (NCT04324450), performed memory tests assessing episodic, procedural, and working memories and were subjected to an rs-fMRI. We manually contoured main structures involved in memory to explore connectivity at rest in a seed-to-voxel analysis. The groups were compared and differences in connectivity were correlated with behavioral scores and irradiation doses. RESULTS: The performance of all mnesic tasks was lower in PFT survivors with a greater alteration in working and episodic memory in irradiated patients. Irradiated survivors had atypical connectivities in all memory circuits compared to controls and in cortico-caudate and cortico-cerebellar circuits compared to non-irradiated survivors. Non-irradiated survivors had only atypical connectivities in the cortico-cerebellar circuits compared to controls. In irradiated survivors, atypical connectivities in cortico-hippocampal circuits were linked with episodic memory scores and dose of irradiation to the left hippocampus and in cortico-striatal circuits with procedural memory scores and dose of irradiation to the striatum. CONCLUSION: The results of this study highlight that irradiation has a long-term impact on brain connectivity in brain circuits involved in memory after pediatric PFT with a specific radiation-dose effect in supratentorial structures.

Impact of a pediatric posterior fossa tumor and its treatments on motor procedural learning.

INTRODUCTION: Posterior fossa tumor (PFT) survivors have difficulty learning new skills. Procedural memory is a skill learning system that allows, through training, the automatization of procedures and progressive improvement of performance. It underlies most of the motor procedures in everyday life that we perform automatically, such as riding a bike or writing. Motor procedural memory is divided into two components: motor sequence learning involving mainly cortico-striatal networks, and motor adaptation involving mainly cortico-cerebellar networks. The aim of this work was to explore the impact of a tumor and its treatment during childhood on procedural learning hypothesizing that sequence learning would be impaired in PFT survivors who have been treated with radiotherapy, whereas motor adaptation would be impaired in all PFT survivors. METHOD: 22 irradiated survivors of PFT, 17 non-irradiated survivors and 21 healthy controls from the IMPALA study (NCT04324450) performed a motor sequence learning task and a motor adaptation task. Doses received by striatal and cerebellar structures were reported from the initial dosimetry plans. RESULTS: Sequence learning was preserved in both tumor groups, but at the individual level 7/22 irradiated, and 4/17 non-irradiated participants failed to learn the motor sequence. Motor adaptation was impaired in both tumor groups, predominantly in the irradiated group. CONCLUSION: This study sheds new light on the long-term impact of PFT treatments in childhood on a rarely-studied part of memory, which is perceptual-motor procedural learning. Our results suggest that the cerebellum and striatum could be considered as organs at risk with regard to procedural learning.