Intrinsic Brain Activity is Associated with the Development and Severity of Glioma
Post by Leanna Kalinowski
The takeaway
Scientists have uncovered an association between higher intrinsic brain activity and the development and severity of gliomas or brain tumors that originate in glial cells.
What's the science?
Gliomas – tumors that originate in glial cells – are the most frequently occurring type of brain tumor. Previous studies have shown that variations in brain activity affect how gliomas behave. For example, the high activity of neurons surrounding gliomas causes an acceleration of tumor growth into those regions. However, it is unknown whether “intrinsic” brain activity – pre-existing levels of activity in healthy controls – impacts glioma occurrence and symptomatology. This week in Brain, Numan and colleagues tested (1) whether brain regions with higher intrinsic brain activity have a higher occurrence of glioma and (2) whether intrinsic brain activity at tumor locations is associated with symptomatology.
How did they do it?
The authors included data from 413 glioma patients across three different cohorts. A glioma mask was drawn for each patient, based on MRI data, to visualize where their tumor was located within the brain. Each mask was then merged into a single heat map per cohort to represent the relative occurrence of tumors within each cohort. To measure symptomatology, the authors reviewed each patient’s medical chart to determine (1) their Karnofsky Performance Status (KPS), which is a standard way to measure a cancer patient’s ability to perform ordinary tasks, and (2) the subtype of their glioma, which indicates its growth potential and aggressiveness.
To collect intrinsic brain activity, 65 healthy controls underwent magnetoencephalography (MEG), which is an imaging technique that measures magnetic fields produced by brain activity. Three measures of brain activity were then calculated from these data: broadband power and offset, which both measure neuronal spiking, and slope, which measures the balance of excitation and inhibition in the brain.
What did they find?
First, when the tumour locations were mapped onto the same locations in the brains of healthy controls, the authors found that greater levels of brain activity (i.e., higher offset values) in controls was associated with a higher occurrence of glioma across all three cohorts. They also found that intrinsic brain activity at individual tumor locations differed based on KPS and glioma subtype. Specifically, grade IV glioblastoma (i.e., the most malignant subtype of glioma) had the lowest ratio of excitation to inhibition, with a lower ratio being associated with a lower KPS (i.e, lower ability to perform ordinary tasks).
What's the impact?
Taken together, these results show that gliomas are more likely to occur in brain regions that have higher intrinsic activity, with the most malignant subtypes of glioma favoring brain regions with a lower ratio of excitation to inhibition. Understanding the relationship between brain activity and gliomas may inform our understanding of glioma, which may aid in the development of more effective treatment strategies in the future.