[tt] Connected to the highways of the brain

[Eugen Leitl]

Connected to the highways of the brain:

A fantastic new study which looked at the 'connectedness' of the human brain
has identified which aspects of the underlying network are the most important
routes of communication.

The research was led by neuroscientist Patric Hagmann and combines brain
imaging with network mathematics to not only visualise the brain's network
but also to understand which are the most important hubs and connections.

The study used diffusion spectrum imaging or DSI to map out the white matter
wiring of the brain in five healthy individuals.

It's a type of diffusion MRI that identifies water molecules and tracks how
they move. In a glass of water, water molecules will move randomly, but when
trapped inside nerve fibres, they move along the length of the fibre,
allowing maps to be created from the average paths of the moving molecules.

The researchers then took the maps of fibres, as illustrated by the top
image, divided the brain up into sections, and created a simplified network
map, shown in the bottom image, which allowed them to mathematically test how
connected the different areas were.

They used network theory, more typically used in social network analysis,
which allows mathematical measures of network properties.

The researchers calculated which areas were the most connected to the rest of
the network in terms of connections going directly in and out of the area,
but also which areas were the most strategically important 'hubs'.

This meant the researchers could identify areas of the cortex that are the
most highly connected and highly important, forming a structural core of the
human brain.

You can see two of the maps on the right. The one in red illustrates which
brain areas are the most highly connected. You can see it's the area at the
top and back of the brain. As you can see better on the original image, its
very centrally located, like a neural mohawk.

The image in blue on the right shows the network 'backbone', the information
highways of the brain.

What's perhaps most interesting it that the most connected brain areas are
many of those which are more active when we're at rest, compared to when
we're engaged in a mental task that requires concentration and effort.

This has been dubbed the 'default network' in the scientific literature, and,
rather annoyingly, the 'daydreaming network' by the popular press.

It's not entirely clear what the network is for, with some studies directly
linked it to 'stimulus independent thought' (yes, daydreaming), while others
more explicitly define it as internally focused, rather than externally
focused thought and cognition.

Unfortunately, most cognitive neuroscience experiments work by measuring the
effect of tasks on brain function, so a brain network which seems to be
switched off by any sort of task is quite hard to study. A recent study found
that even the noise of the brain scanner affects it.


Link to PLoS Biology article on brain connectivity.
http://biology.plosjournals.org/perlserv/?request=get-document&doi=10.1371/journal.pbio.0060159

Link to write-up from The New York Times.
http://www.nytimes.com/2008/07/01/health/research/01brain.html?partner=rssuserland&emc=rss&pagewanted=all

Link to write-up from Neurophilosophy.
http://scienceblogs.com/neurophilosophy/2008/07/hi_res_brain_topology_map.php

Link to write-up from Science News.
http://sciencenews.org/view/generic/id/33747/title/Journey_to_the_center_of_the_brain