July 29, 2011
Ashesh Mehta, MD
In today’s world, networks operate in diverse situations, from communication networks that permit a cell phone conversation to social networks that link friends on Facebook. These networks have properties (e.g., each computer in your home with a wireless network) and hubs, where multiple separate sub-networks come together (e.g., a person who bridges multiple social networks).
It is increasingly being recognized that these properties operate in our brain too – in both normal functioning and as a mechanism for disorders of the nervous system, like the spread of seizures
across the brain. Functional magnetic resonance imaging
(fMRI) is a non-invasive method that can be used to measure the tiny metabolic changes that take place in an active part of the brain.
To date, fMRI has been typically used to study what parts of the brain become active when subjects respond to stimuli (e.g., being shown pictures) or perform tasks (e.g., rotating objects in their mind’s eye). Recently, there has been interest in looking at how the brain works at rest, by measuring the fMRI signals in different brain regions and seeing how they activate and deactivate together. By measuring the relationship of activity between different brain areas, it is possible to describe an individual’s brain network, including sub-networks where brain areas with higher correlation are more closely connected (much like friends in a social network). While this has been studied extensively with fMRI, results have been difficult to interpret, because of the unclear relationship between fMRI signals and brain electrical activity.
Validation of this fMRI methodology has recently taken a major step forward, with the findings published in a recent issue of Proceedings of the National Academy of Sciences
. The authors at the Hofstra North Shore-LIJ School of Medicine’s Comprehensive Epilepsy Care Center
have demonstrated that the network architecture revealed by fMRI predicts the results of brain mapping with direct electrical stimulation. In the study, scientists and doctors studied patients with epilepsy
who were undergoing surgery in order to pinpoint where seizures start in the brain. First, the patients underwent the fMRI tests to define the brain networks prior to the surgery to implant the electrodes. Then investigators directly measured brain electrical activity using the implanted electrodes. They showed that the fMRI network architecture predicted the patients’ brain connections involved both during normal brain function and seizure spreading.
These findings highlight the importance of applying network theory to brain function, and confirm the ability of fMRI to map the network architecture of the brain. This study represents an important step in understanding brain function, and one with implications for treating a diversity of diseases from epilepsy to autism.
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