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Fast scans catch brain snoozing and wide awake

WASHINGTON U.-ST. LOUIS (US) — Scientists have used a speedier imaging technology to track brain activity in volunteers at rest and while they watched a movie.

The faster scans are offering new insights into how brain regions work with each other in cooperative groups called networks.

“Brain activity occurs in waves that repeat as slowly as once every 10 seconds or as rapidly as once every 50 milliseconds,” says senior researcher Maurizio Corbetta, a neurology professor at Washington University School of Medicine in St. Louis. “This is our first look at these networks where we could sample activity every 50 milliseconds, as well as track slower activity fluctuations that are more similar to those observed with functional magnetic resonance imaging (fMRI).

“This analysis performed at rest and while watching a movie provides some interesting and novel insights into how these networks are configured in resting and active brains.”

Understanding how brain networks function is important for better diagnosis and treatment of brain injuries, according to Corbetta.

Researchers know of several resting-state brain networks, which are groups of different brain regions whose activity levels rise and fall in sync when the brain is at rest. Scientists used fMRI to locate and characterize these networks, but the relative slowness of this approach limited their observations to activity that changes every 10 seconds or so.

‘Much like a radio’

A surprising result from fMRI was that the spatial pattern of activity (or topography) of these brain networks is similar at rest and during tasks.

In contrast, a faster technology called magnetoencephalography (MEG) can detect activity at the millisecond level, letting scientists examine waves of activity in frequencies from slow (0.1-4 cycles per second) to fast (greater than 50 cycles per second).

“Interestingly, even when we looked at much higher temporal resolution, brain networks appear to fluctuate on a relatively slow time scale,” says first author Viviana Betti, a postdoctoral researcher at the Institute of Technology and Advanced Biomedical Imaging at the University of Chieti, Italy.

“However, when the subjects went from resting to watching a movie, the networks appeared to shift the frequency channels in which they operate, suggesting that the brain uses different frequencies for rest and task, much like a radio.”

In the study, the scientists asked one group of volunteers to either rest or watch the movie during brain scans. A second group was asked to watch the movie and look for event boundaries, moments when the plot or characters or other elements of the story changed. They pushed a button when they noticed these changes.

As in previous studies, most subjects recognized similar event boundaries in the movie. The MEG scans showed that the communication between regions in the visual cortex was altered near the movie boundaries, especially in networks in the visual cortex.

“This gives us a hint of how cognitive activity dynamically changes the resting-state networks,” Corbetta says. “Activity locks and unlocks in these networks depending on how the task unfolds. Future studies will need to track resting-state networks in different tasks to see how correlated activity is dynamically coordinated across the brain.”

The European Community’s Seventh Framework Programme Grant Agreement (BrainSynch); the Human Connectome Project; the University of Chieti; and the National Institute of Health funded the research, which was reported in the journal Neuron.

Source: Washington University in St. Louis

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