Date Published: July 10, 2017
Publisher: Public Library of Science
Author(s): Johanna L. Reichert, Monika Chocholous, Ulrike Leiss, Thomas Pletschko, Gregor Kasprian, Julia Furtner, Kathrin Kollndorfer, Jacqueline Krajnik, Irene Slavc, Daniela Prayer, Thomas Czech, Veronika Schöpf, Christian Dorfer, Marta M. Alonso.
While it has been shown that cerebellar tumor lesions have an impact on cognitive functions, the extent to which they shape distant neuronal pathways is still largely undescribed. Thus, the present neuroimaging study was designed to investigate different aspects of cognitive function and their neuronal correlates in patients after childhood cerebellar tumor surgery. An alertness task, a working memory task and an incompatibility task were performed by 11 patients after childhood cerebellar tumor surgery and 17 healthy controls. Neuronal correlates as reflected by alterations in functional networks during tasks were assessed using group independent component analysis. We were able to identify eight networks involved during task performance: default mode network, precuneus, anterior salience network, executive control network, visual network, auditory and sensorimotor network and a cerebellar network. For the most ‘basic’ cognitive tasks, a weaker task-modulation of default mode network, left executive control network and the cerebellar network was observed in patients compared to controls. Results for higher-order tasks are in line with a partial restoration of networks responsible for higher-order task execution. Our results provide tentative evidence that the synchronicity of brain activity in patients was at least partially restored in the course of neuroplastic reorganization, particularly for networks related to higher-order cognitive processes. The complex activation patterns underline the importance of testing several cognitive functions to assess the specificity of cognitive deficits and neuronal reorganization processes after brain lesions.
In children, brain tumors are the second most common neoplasms, after leukemia, and constitute 25 percent of all childhood cancers. Tumors of the posterior fossa, including the brain stem and the cerebellum, account for 50 percent of all brain tumors in children [1–3] and comprise pathologies such as medulloblastoma, cerebellar astrocytoma, ependymoma, and brainstem glioma .
The presented study was part of a larger study protocol, which was evaluated and approved by the ethics committee of the Medical University of Vienna (EK No. 370/2011) according to the Declaration of Helsinki.
The aim of the present study was to assess the long-term impact of cerebellar lesions after tumor treatment on cognitive functions and on global functional brain networks. Thus, during fMRI scanning, patients and healthy controls took part in three cognitive tasks covering an array of executive functions. Functionally connected networks during the tasks were identified by means of group independent component analysis (group ICA). Overall, several networks showed a decreased task-modulation in patients compared to controls, particularly in those tasks posing less cognitive demands. Fewer differences in functional networks were observed during cognitively more demanding tasks, possibly indicating a restoration of functional connectivity within networks involved in higher-order cognitive functions.
Although our sample was very homogenous regarding tumor type, tumor location, time between surgery and experiment, and age-matching of healthy controls, there was a large time gap (mean 56 days) between the neuropsychological testing and MRI measurements. Although spontaneous neuronal reorganization during this time is very unlikely, as the surgery of our patients had been conducted long before (7–20 years), we cannot exclude other possible confounds arising from this gap. Moreover, the small sample size resulting from the selection of a homogeneous patient group may be a limiting factor in the interpretation of our results.
In summary, patients in our study showed no impairments in general cognitive functioning (as reflected by IQ scores) and only slightly impaired performance in the three specific cognitive tasks (working memory, incompatibility, and alertness) conducted.