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Mapping the brain
have moved a step closer to being able to develop a computer model of
the brain after developing a technique to map both the connections and
functions of nerve cells in the brain together for the first time.
A new area of research is emerging in the neuroscience known as ‘connectomics’.
With parallels to genomics, which maps the our genetic make-up,
connectomics aims to map the brain’s connections (known as ‘synapses’).
By mapping these connections – and hence how information flows through
the circuits of the brain – scientists hope to understand how
perceptions, sensations and thoughts are generated in the brain and how
these functions go wrong in diseases such as Alzheimer’s disease,
schizophrenia and stroke.
Mapping the brain’s connections is no trivial task, however: there are
estimated to be one hundred billion nerve cells (‘neurons’) in the
brain, each connected to thousands of other nerve cells – making an
estimated 150 trillion synapses. Dr Tom Mrsic- Flogel, a Wellcome Trust
Research Career Development Fellow at UCL (University College London),
has been leading a team of researchers trying to make sense of this
“How do we figure out how the brain’s neural circuitry works?” he asks.
“We first need to understand the function of each neuron and find out to
which other brain cells it connects. If we can find a way of mapping the
connections between nerve cells of certain functions, we will then be in
a position to begin developing a computer model to explain how the
complex dynamics of neural networks generate thoughts, sensations and
Nerve cells in different areas of the brain perform different functions.
Dr Mrsic-Flogel and colleagues focus on the visual cortex, which
processes information from the eye. For example, some neurons in this
part of the brain specialise in detecting the edges in images; some will
activate upon detection of a horizontal edge, others by a vertical edge.
Higher up in visual hierarchy, some neurons respond to more complex
visual features such as faces: lesions to this area of the brain can
prevent people from being able to recognise faces, even though they can
recognise individual features such as eyes and the nose, as was famously
described in the book The Man Who Mistook His Wife for a Hat by Oliver
In a study published online 11 April 2011 in the journal Nature, the
team at UCL describe a technique developed in mice which enables them to
combine information about the function of neurons together with details
of their synaptic connections.
The researchers looked into the visual cortex of the mouse brain, which
contains thousands of neurons and millions of different connections.
Using high resolution imaging, they were able to detect which of these
neurons responded to a particular stimulus, for example a horizontal
Taking a slice of the same tissue, the researchers then applied small
currents to a subset of neurons in turn to see which other neurons
responded – and hence which of these were synaptically connected. By
repeating this technique many times, the researchers were able to trace
the function and connectivity of hundreds of nerve cells in visual
The study has resolved the debate about whether local connections
between neurons are random – in other words, whether nerve cells connect
sporadically, independent of function – or whether they are ordered, for
example constrained by the properties of the neuron in terms of how it
responds to particular stimuli. The researchers showed that neurons
which responded very similarly to visual stimuli, such as those which
respond to edges of the same orientation, tend to connect to each other
much more than those that prefer different orientations.
Using this technique, the researchers hope to begin generating a wiring
diagram of a brain area with a particular behavioural function, such as
the visual cortex. This knowledge is important for understanding the
repertoire of computations carried out by neurons embedded in these
highly complex circuits. The technique should also help reveal the
functional circuit wiring of regions that underpin touch, hearing and
“We are beginning to untangle the complexity of the brain,” says Dr
Mrsic- Flogel. “Once we understand the function and connectivity of
nerve cells spanning different layers of the brain, we can begin to
develop a computer simulation of how this remarkable organ works. But it
will take many years of concerted efforts amongst scientists and massive
computer processing power before it can be realised.” – Source: UCL
of upload: 15th Aug 2011