May 31, 2011

New Method To Measure Mental States

(Ivanhoe Newswire) -- New clues to the mystery of brain function, obtained through research by scientists at the Stanford University School of Medicine, suggest that distinct mental states can be distinguished based on unique patterns of activity in coordinated "networks" within the brain. These networks consist of brain regions that are synchronously communicating with one another. The Stanford team is using this network approach to develop diagnostic tests in Alzheimer's disease and other brain disorders in which network function is disrupted.

A team of researchers led by Michael Greicius, MD, assistant professor of neurology and neurological sciences, was able to determine from brain-imaging data whether experimental subjects were recalling events of the day, singing silently to themselves, performing mental arithmetic or merely relaxing. In the study, subjects engaged in these mental activities at their own natural pace, rather than in a controlled, precisely timed fashion as is typically required in experiments involving the brain-imaging technique called functional magnetic resonance imaging. This suggests that the new method "” a variation on the fMRI procedure "” could help scientists learn more about what the brain is doing during the free-flowing mental states through which individuals move, minute-to-minute, in the real world.

In their analysis, the Stanford team broke free of this scripted approach by looking not for brain regions that showed heightened activity during one mental state versus another, but for coordinated activity between brain regions, defining distinct brain states. This let subjects think in a self-paced manner more closely resembling the way they think in the world outside the MRI scanner. Instead of breaking up a cognitive state into short blocks of task and non-task, Greicius and his team used uninterrupted scan periods ranging from 30 seconds to 10 minutes in length, allowing subjects to follow their own thought cues at their own pace. The scientists were able to accurately capture subjects' mental states even when the duration of the scans was reduced to as little as one minute or less "” all the more reflective of real-world cognition.

Greicius's team assembled images from each separate scan. Instead of comparing "on-task" images with "off-task" images to see which regions were active during a distinct brain state compared with when the brain wasn't in that state, the researchers focused on which collections, or networks, of brain regions were active in concert with one another throughout a given state.

In their analysis, the Stanford team identified groups of regions throughout the brain whose activity was correlated to form functional networks.

Once they had completed their mapping of the four mental states to specific patterns of connectivity across the 90 brain regions.

The ability to use fMRI in a more casual, true-to-life manner for capturing the mental states of normal volunteers bodes well for assessing patients with cognitive disorders, such as people with Alzheimer's disease or other dementias, who are often unable to follow the precise instructions and timing demands required in traditional fMRI.

SOURCE: Stanford Press Release, May 2011