Source of OM Within?
- A Butterfly Effect In The Brain
Next time your brain plays tricks on you,
you have an excuse: according to new research
by UCL scientists published in the journal
Nature, the brain is intrinsically unreliable.
This may not seem surprising to most of us,
but it has puzzled neuroscientists for decades.
Given that the brain is the most powerful
computing device known, how can it perform
so well even though the behaviour of its circuits is variable?
A long-standing hypothesis is that the brain's
circuitry actually is reliable and the
apparently high variability is because your
brain is engaged in many tasks simultaneously,
which affect each other.
It is this hypothesis that the researchers
at UCL tested directly. The team a collaboration
between experimentalists at the Wolfson Institute
for Biomedical Research and a theorist, Peter
Latham, at the Gatsby Computational Neuroscience
Unit took inspiration from the celebrated
butterfly effect from the fact that the flap
of a butterfly's wings in Brazil could set off
a tornado in Texas. Their idea was to introduce
a small perturbation into the brain, the
neural equivalent of butterfly wings, and
ask what would happen to the activity in
the circuit. Would the perturbation grow and
have a knock-on effect, thus affecting the
rest of the brain, or immediately die out?
It turned out to have a huge knock-on effect.
The perturbation was a single extra 'spike',
or nerve impulse, introduced to a single
neuron in the brain of a rat. That single
extra spike caused about thirty new extra
spikes in nearby neurons in the brain, most
of which caused another thirty extra spikes,
and so on. This may not seem like much, given
that the brain produces millions of spikes
every second. However, the researchers estimated
that eventually, that one extra spike affected
millions of neurons in the brain.
"This result indicates that the variability
we see in the brain may actually be due to
noise, and represents a fundamental feature
of normal brain function," said lead author
Dr. Mickey London, of the Wolfson Institute
for Biomedical Research, UCL.
This rapid amplification of spikes means
that the brain is extremely 'noisy' much,
much noisier than computers. Nevertheless,
the brain can perform very complicated tasks
with enormous speed and accuracy, far faster
and more accurately than the most powerful
computer ever built (and likely to be built
in the foreseeable future). The UCL researchers
suggest that for the brain to perform so well
in the face of high levels of noise, it must
be using a strategy called a rate code. In a
rate code, neurons consider the activity of
an ensemble of many neurons, and ignore the
individual variability, or noise, produced
by each of them.
So now we know that the brain is truly noisy,
but we still don't know why. The UCL researchers
suggest that one possibility is that it's the
price the brain pays for high connectivity
among neurons (each neuron connects to about
10,000 others, resulting in over 8 million
kilometres of wiring in the human brain).
Presumably, that high connectivity is at
least in part responsible for the brain's
computational power. However, as the research
shows, the higher the connectivity, the noisier
the brain. Therefore, while noise may not be
a useful feature, it is at least a by-product
of a useful feature.
Source: University College London - UCL
Article URL: http://www.medicalnewstoday.com/articles/193482.php
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