It has long been suspected that humans do not
experience the world continuously, but rather in rapid snapshots.
Now,
researchers at the University of Glasgow have demonstrated this is indeed the
case. Just as the body goes through a 24-hour sleep-wake cycle controlled by a circadian clock, brain function undergoes
such cyclic activity – albeit at a much faster rate.
Professor
Gregor Thut of the Institute of Neuroscience and Psychology, said: “Rhythms are
intrinsic to biological systems. The circadian rhythm, with its very slow periodicity
of sleep and wake
cycles every 24 hours has an obvious, periodic effect on bodily functions.
“Brain
oscillations – the recurrent neural activity that we see in the brain – also
show periodicity but cycle at much faster speeds. What we wanted to know was
whether brain function was affected in a cyclic manner by these rapid
oscillations.”
The
researchers studied a prominent brain rhythm associated with visual cortex
functioning that cycles at a rate of 10 times per second (10Hz).
They
used a ‘simple trick’ to affect the oscillations of this rhythm which involved
presenting a brief sound to ‘reset’ the oscillation.
Testing
subsequent visual perception, by using transcranial magnetic stimulation of the
visual cortex, revealed a cyclic pattern at the very rapid rate of brain oscillations, in time
with the underlying brainwaves.
Prof
Thut said: “Rhythmicity therefore is indeed omnipresent not only in brain
activity but also brain
function.
For
perception, this means that despite experiencing the world as a continuum, we
do not sample our world continuously but in discrete snapshots determined by
the cycles of brain rhythms.”
The
research, ‘Sounds reset rhythms of visual cortex and
corresponding human visual perception’ is published in the journal Current
Biology.
More
information: Romei
et al., Sounds Reset Rhythms of Visual Cortex and Corresponding Human Visual
Perception, Current Biology (2012),doi:10.1016/j.cub.2012.03.025
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