Brain stimulation and functional MRI work together
Researchers at University College London’s Institute of Cognitive
Neuroscience have found that human peripheral vision can be positively affected
by stimulating parts of the brain with brief electromagnetic pulses. Led by Christian
C. Ruff and Jon Driver, they applied transcranial magnetic stimulation to a section
of the frontal cortex — which plays a role in generating eye movements —
while simultaneously recording activity with a scanner in connected brain regions.
The stimulation process involved holding a magnetic
coil next to the skull and moving it over a particular section of the brain. The
coil created magnetic fields, inducing small electrical currents that alter the
activity of neural pathways, increasing or inhibiting that activity. Functional
MRI was used to measure the neural activity because it can track the blood oxygen
supply to neurons. More active neurons will exhibit higher oxygen and energy consumption.
Combining the techniques allowed the
researchers to directly measure the effects of the stimulation on the neurons, both
under the coil and in remote areas of the brain. They measured how the stimulated
brain area involved in eye movement can influence activity in other connected regions,
such as those involved with vision.
As reported in the Aug. 8 issue of
Current Biology, transcranial magnetic stimulation appeared to enhance activity
in the visual cortex, almost as if the brain were receiving visual information.
It was as if eye movement had taken place when, in fact, the eye remained still.
Participants in the study were asked to compare the brightness of objects, as presented
on a computer monitor, in the periphery or in the center of the screen. These perceptual
tests verified that, with the stimulation to an area of the frontal cortex, the
participants experienced better peripheral vision.
This combination of transcranial magnetic
stimulation and functional MRI could lead to greater understanding and treatment
of neurological disorders that can affect vision or other brain functions —
such as the aftereffects of a stroke.
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