readings> the 10 percent myth
It is a well known “fact” that we use just
10
percent of our brains. This is why creativity gurus are always urging
us to learn to tap the other silent 90 percent. It has also
been a staple point for those who want to argue that consciousness has
little to do with brain circuitry and more to do with some intangible
soul-stuff.
So where did this particular old wives’ tale spring from?
Well, there are at least three famous bits of neuroscientific research
that have fed the myth. And here are the modern countering arguments.
In the 1920s, the behaviourist psychologist Karl Lashley carried out an
experiment in which he trained rats to run a maze and then chopped away
increasing amounts of their cortex to find out which grey matter bump
might house the memory trace for the route. Lashley was surprised to
find that what counted was not which part he cut out, just how much. So
the memory seemed evenly spread over the brain tissue.
Today we can answer that memories are indeed distributed across the
cortex – though not evenly, but in a hierarchically organised
fashion. The visual aspects of a memory will find their way to visual
areas of the cortex, olfactory cues to the olfactory regions. And while
parts of the brain like the hippocampus are specialist memory organs,
they play a role mostly at specific stages like the fixing and
recalling of memories.
Furthermore, Lashley’s study did not
even cut into lower brain centres like the basal ganglia which would
have carried the most habitual or over-learnt aspects of the response
(McCrone 1999). We now know that any kind of mental activity is the
result of a team effort by the brain’s hierarchy and so
damage to one area normally degrades rather than eradicates the ability
to perform.
Of course, Lashley was no fool and rightly concluded that his
experiment merely showed that brain organisation was far more dynamic
and distributed than existing theories recognised (Lashley 1930). But
the indelible image of almost brainless rats still running mazes
encouraged others to wonder if the cortex really did anything at all?
Then in the 1930s, the pioneering Canadian neurosurgeon Wilder Penfield
probed the brains of his patients with an electrode while operating on
them for epilepsy. Such surgery is carried out while the patients are
conscious and able to talk about what they are experiencing. The
probing is done to ensure that surgery is not cutting into any vital
areas like the language centres.
Famously, Penfield found that jolts to
some regions sparked vivid imaginary scenes or surges of emotion. But
equally he was puzzled that there were large areas of "silent" cortex
where he got no reaction. Penfield later came to argue that this
uncertain connection between physical stimulation and mental response
meant that there must be more to being a mind than just a set of brain
circuits (Penfield, 1975).
The modern view on these silent regions is that Penfield was simply
using too crude a stimulus to stir the more delicate integrative parts
of the cortex. Again, the brain being a distributed hierarchy, it seems
that while the lower processing areas, such as the primary sensory
cortices, will respond quite readily to an electrode, trying to
interpret it as a real sensory event, the higher areas need to be
hearing from a wider range of inputs to start to find any concrete
meaning in them.
Nevertheless, vivid newspaper accounts of Penfield’s and
Lashley’s work helped foster the myth that much of the
cortex, our wrinkled grey hemispheres, appeared mysteriously unused, or
at least not completely necessary for everyday mental function.
Einstein even jokingly declared that these untapped regions of the
brain must be the secret of his own success, showing just how quickly
this factoid entered into popular folklore.
However today when
anti-abortionists argue before Parliamentary committees about foetal
sentience and cortical development, or psychologists rail against
research linking IQ to brain volume, it is the research of an English
neurologist, John Lorber, that still really gets them going.
In the 1970s, Lorber was part of a world-leading spinal surgery team at
Sheffield Children's Hospital treating kids with spina bifida. A
frequent complication of this complaint is hydrocephalus where the
fluid-filled ventricles in the middle of the brain expand, causing the
cortex to be squashed against the bone of the skull. This can leave
sufferers severely mentally handicapped or even kill them. Lorber was
inserting shunts – plastic valves – to drain the
cerebral fluid and so relieve the pressure.
What surprised Lorber was that a few of his patients showed no outward
sign of mental deterioration and yet X-rays revealed "wall to wall"
ventricles. The chambers had ballooned to such an extent that there was
barely any cortex visible inside the skull.
The most celebrated case
was that of a 26-year-old student at the University of Sheffield who
had an IQ of 126 and a first-class honours degree in mathematics. This
was despite a cortical mantle apparently crushed to paper thinness, the
usual four or five centimetres having been reduced to a bare millimetre
or so. Lorber estimated that the man's whole brain weighed only about
100 grams compared to the adult average of about 1500 grams.
So an honours student with a brain mass not much more than that of a
dog or monkey! Little wonder that Lorber was moved to ask: "Is your
brain really necessary?" when talking up his findings at medical
conferences. Or that the journal Science headlined with the very same
question when it picked up on the story (Lewin 1980).
The X-rays did
make many people wonder what was the point of millions of years of
careful evolutionary tuning to develop the very large and complex human
brain if it still worked just as well when reduced to no more than a
slick of neural tissue.
Lorber’s claims were never publicly refuted. And Lorber - who
died in 1996 - stuck firmly to his story, claiming that in 500 CT scans
he had found many hydrocephalics with hardly any brain left above the
level of the brainstem and yet living ordinary lives (Lorber, 1981). So
a little detective work was needed to get to the bottom of this one.
Talking to colleagues and contemporaries of Lorber, it was revealed he
was probably greatly exaggerating the extent of brain loss in his
cases. Said one source: "If the cortical mantle actually had been
compressed to a couple of millimetres, it wouldn't even have shown up
on his X-rays."
Another agreed, adding that brain scans with modern
techniques such as MRI (magnetic resonance imaging) show stretching,
but not much real loss of brain weight with slow-onset hydrocephalus.
He says the brain structure adapts to the space it is allowed: "The
cortex and its connections are still there, even if grossly distorted."
Sufferers with hydrocephalus also report many subtle symptoms that
don’t show up in standard tests of cognition. They do well on
basic reading and arithmetic or IQ-type questions, but struggle with
focused attention, spatial imagination, general motor co-ordination,
and other skills that rely on longer-range integrative links across the
brain.
This fits a picture of a brain in which all the cortical
processing regions are in place but where the white matter –
the wealth of insulated connections that actually occupies much of the
centre of the cerebral hemispheres – has been pulled out of
shape.
So Lorber’s results were striking but overplayed. And
certainly the rise of neuroimaging over the past decade ought finally
to have put paid to this long-running myth about the 10 percent brain.
One of the most important lessons from the first scanning studies of
brains actually caught in the act of thinking – with areas
lighting up with increased metabolic activity – was just how
widespread were the patterns of activation for the most minor mental
responses. No areas were silent, just relatively active or inactive in
forming the reaction to the moment.
As Lashley came to realise, the brain is not a simple device but a
complex organ whose supple logic we are only beginning to be able to
appreciate. New kinds of causal thinking are needed to model systems in
which there is a localisation of function yet also global cohesion
(McCrone 2004). Nevertheless you can be pretty sure that without any
special effort on your part, you are indeed using the whole of your
brain the whole of the time.
References
Lashley KS. Basic neural mechanisms in behavior. Psychological Review,
37:1-24 (1930).
http://psychclassics.yorku.ca/Lashley/neural.htm
Penfield W. The Mystery of Mind, Princeton University Press (1975).
Lewin R. Is your brain really necessary? Science, 210:1232-4 (1980).
Lorber J. Is your brain really necessary? Nursing Mirror, 152:29-30
(1981)