Key language areas of the brain act like connectors in social networks

When surgeons perform brain surgery on patients with brain tumors or epilepsy, they must remove tumors or abnormal tissue while preserving parts of the brain that control language and movement.

what's new

A new Northwestern Medicine study may help doctors better decide which brain regions to preserve and improve patients' language function after brain surgery. The study improves understanding of how language is encoded in the brain and identifies key characteristics of key parts of the cerebral cortex that work together to produce language.

Why is this important?

If you think of the brain's language network as a social network, scientists have essentially discovered a person who connects many sub-networks. Without this person, people would never know each other. In the brain, these “connectors” perform the same function for language: if the connector sites are removed, patients will make more language errors after surgery (such as having trouble naming objects) because the sub-networks can't work together.

process

Scientists at Northwestern University identified important language connections by recording electrical signals from the brain cortex while patients with epilepsy or brain tumors read words aloud. The researchers then used graph theory techniques and machine learning to analyze the signals and predict which parts of the network were important.

“This discovery could help us work more precisely and efficiently when mapping language sites before surgery,” said corresponding author Dr. Mark Slutsky, a professor of neurology at Northwestern University Feinberg School of Medicine and a neurologist at Northwestern Medicine. “It could help enhance how surgeons do this mapping, ultimately allowing them to reduce the time needed for stimulation or even eliminate stimulation and only record electrical signals.”

Patients with brain tumors or epilepsy who need surgery often undergo functional mapping, which involves direct electrical stimulation of the brain to identify important parts of the brain, particularly the cerebral cortex, and help neurosurgeons determine which areas should not be removed to preserve language function. For example, electrical stimulation may temporarily interfere with the ability to speak or remember the names of objects, suggesting that the stimulated area is important for speech or language function.

Current stimulation technology has limitations

“Although the method has remained largely unchanged for over 50 years, we still don't really understand what happens during this stimulation,” Slutsky said. “It's not clear what's special about the focal regions that are identified by stimulation as important for language and speech.

“Many areas in the brain are active when people speak, but only a handful of these have been identified as important for that function by being disturbed during stimulation. Answering this question may help us understand how electrical stimulation affects the brain and how the brain produces spoken language.”

An estimated 1.2 million people in the United States suffer from brain tumors.

Currently, many brain tumor patients undergo 20 to 60 minutes of stimulation while awake during surgery. This technology is not perfect at identifying the language site. Results can be false negative or false positive, and the process can cause seizures.

“It's not fun for the patient,” Slutsky says. “When you do this with epilepsy patients, it takes a day, sometimes two days, to map, and it's exhausting for the patient.”

Slutsky said epilepsy patients may need brain surgery if medication doesn't adequately control their seizures.

Note

Other study authors from Northwestern University are Jason K. Hsieh, Prashanth R. Prakash, Robert D. Flint, Zachary Fitzgerald, Emily Mugler, Jessica W. Templer, Joshua M. Rosenow and Matthew C. Tate.

The Northwestern study was a collaboration between Nathan Krohn and Eugene Wang of Johns Hopkins University and Richard Betzel of Indiana University.

The research was funded by the National Institute of Neurological Disorders and Stroke at the National Institutes of Health, the Doris Duke Charitable Foundation, the Northwestern Memorial Foundation Dixon Translational Research Grant and the Northwestern Medicine Malnati Brain Tumor Institute at the Robert H. Lurie Comprehensive Lurie Cancer Center at Northwestern University.