IMAGINATION, REALITY FLOW IN OPPOSITE DIRECTIONS IN THE BRAIN
As real as that daydream may seem, its path through your brain runs
opposite reality.
Aiming to discern
discrete neural circuits, researchers at the University of Wisconsin-Madison
have tracked electrical activity in the brains of people who alternately
imagined scenes or watched videos.
"A really
important problem in brain research is understanding how different parts of the
brain are functionally connected. What areas are interacting? What is the
direction of communication?" says Barry Van Veen, a UW-Madison professor
of electrical and computer engineering. "We know that the brain does not
function as a set of independent areas, but as a network of specialized areas
that collaborate."
Van Veen, along with
Giulio Tononi, a UW-Madison psychiatry professor and neuroscientist, Daniela
Dentico, a scientist at UW-Madison's Waisman Center, and collaborators from the
University of Liege in Belgium, published results recently in the journal NeuroImage.
Their work could lead to the development of new tools to help Tononi untangle
what happens in the brain during sleep and dreaming, while Van Veen hopes to
apply the study's new methods to understand how the brain uses networks to
encode short-term memory.
During imagination,
the researchers found an increase in the flow of information from the parietal
lobe of the brain to the occipital lobe -- from a higher-order region that
combines inputs from several of the senses out to a lower-order region.
In contrast, visual
information taken in by the eyes tends to flow from the occipital lobe -- which
makes up much of the brain's visual cortex -- "up" to the parietal
lobe.
"There seems to
be a lot in our brains and animal brains that is directional, that neural signals
move in a particular direction, then stop, and start somewhere else,"
says. "I think this is really a new theme that had not been
explored."
The researchers
approached the study as an opportunity to test the power of
electroencephalography (EEG) -- which uses sensors on the scalp to measure
underlying electrical activity -- to discriminate between different parts of
the brain's network.
Brains are rarely
quiet, though, and EEG tends to record plenty of activity not necessarily
related to a particular process researchers want to study.
To zero in on a set of
target circuits, the researchers asked their subjects to watch short video
clips before trying to replay the action from memory in their heads. Others
were asked to imagine traveling on a magic bicycle -- focusing on the details
of shapes, colors and textures -- before watching a short video of silent
nature scenes.
Using an algorithm Van
Veen developed to parse the detailed EEG data, the researchers were able to
compile strong evidence of the directional flow of information.
"We were very
interested in seeing if our signal-processing methods were sensitive enough to
discriminate between these conditions," says Van Veen, whose work is
supported by the National Institute of Biomedical Imaging and Bioengineering.
"These types of demonstrations are important for gaining confidence in new
tools."
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