How to speak the language of thought
We are now beginning to crack the brain’s code, which allows us to
answer such bizarre questions as “what is the speed of thought?
Human
brains grow most rapidly just after birth and reach half their adult
size within three months, according to a study in JAMA Neurology.
When he was asked, as a joke, to explain how the mind works in five
words, cognitive scientist Steven Pinker didn't hesitate. "Brain cells
fire in patterns", he replied. It's a good effort, but all it really
does is replace one enigma with another mystery.
It’s long been
known that brain cells communicate by firing electrical signals to each
other, and we now have myriad technologies for recording their patterns
of activity – from electrodes in the brain or on the scalp, to
functional magnetic resonance scanners that can detect changes in blood
oxygenation. But, having gathered these data, the meaning of these
patterns is still an enduring mystery. They seem to dance to a tune we
can't hear, led by rules we don't know.
Neuroscientists speak of
the neural code, and have made some progress in cracking that code. They
are figuring out some basic rules, such as when cells in specific parts
of the brain are likely to light up depending on the task at hand.
Progress has been slow, but in the last decade various research teams
around the world have been pursuing a far more ambitious project. We may
never be able to see the complete code book, they realised, but by
trying to write our own entries, we can begin to pick apart the ways
that different patterns correspond to different actions.
Albert
Lee and Matthew Wilson, at the Massachusetts Institute of Technology
(MIT) first helped to set out the principles in 2002. It progresses like
this. First, we record from the brain of a rat – one of our closer
relatives, in the grand tree of life – as it runs a maze. Studying the
whole brain would be too ambitious, so we can focus our recording on an
area known as the hippocampus, known to be important for navigation and
memory. If you've heard of this area before it is probably because of a
famous result which showed that London taxi drivers developed larger hippocampi the longer they had spent navigating the streets of England's sprawling capital.
It doesn’t allow us to
completely crack the code, because we still don't know all the rules,
and it can’t help us read the patterns which aren't from this bit of the
brain or which aren't about maze running, but it is still a powerful
tool. For instance, using this technique, the team was able to show
that the specific sequence of cell firing repeated in the brain of the
rat when it slept after running the maze (and, as a crucial comparison,
not in the sleep it had enjoyed before it had run the maze).
Fascinatingly, the sequence repeated faster during sleep –
around 20 times faster. This meant that the rat could run the maze in
their sleeping minds in a fraction of the time it took them in real
life. This could be related to the mnemonic function of sleep; by replaying the memory, it might have helped the rat to consolidate its learning.
And the fact that the replay was accelerated might give us a glimpse of
the activity that lies behind sudden insights, or experiences where our
life “flashes before our eyes”; when not restrained, our thoughts
really can retrace familiar paths in “fast forward”. Subsequent work has
shown that these maze patterns can run backwards as well as forwards - suggesting that the rats can imagine a goal, like the end of the maze, and work their way back from that to the point where they are.
One application of techniques like these, which are equal
parts highly specialised measurement systems and fiercely complicated
algorithms, has been to decode the brain activity in patients who are locked in or in a vegetative state.
These patients can’t move any of their muscles, and yet they may still
be mentally aware and able to hear people talking to them in the same
room. First, the doctors ask the patients to imagine activities which
are known to active specific brain regions – such as the hippocampus.
The data is then decoded so that you know which brain activity
corresponds to certain ideas. During future brain scans, the patients
can then re-imagine the same activities to answer basic questions. For
instance, they might be told to imagine playing tennis to answer yes and
walking around their house to answer no – the first form of
communication since their injury.
There are other applications, both theoretical science,
to probe the inner workings of our minds, and practical domains such as
brain-computer interfaces. If, in the future, a paraplegic wants to
control a robot arm, or even another person,
via a brain interface, then it will rely on the same techniques to
decode information and translate it into action. Now the principles have
been shown to work, the potential is staggering.
I don't like BBC. A lot of lies from it.
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