Mind Hacks

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.
Link to write-up from The New York Times.
Link to write-up from Neurophilosophy.
Link to write-up from Science News.

This week’s ABC Radio National’s All in the Mind discusses what happens in the brain during out of body experiences, and why actions can be accurate even when our perceptions are not.

The first interview is with neurologist Olaf Blanke who discusses some of his recent compelling research, including a virtual reality experiment to induce out-of-body touch sensations in healthy participants and one with implanted brain electrodes to trigger full-blown out-of-body experiences in patients undergoing neurosurgery.

The second interview is with psychologist Melvyn Goodale, famous for his work on distinguishing the visual streams in the brain: the dorsal stream and the ventral stream.

Some of the most striking and important results from this work come from patients who have suffered damage to one or the other stream.

In the programme, Goodale talks about brain-injured patient DF, who can correctly and accurately grasp objects she cannot consciously ‘see’. The opposite has been found in other patients, who can accurately see and describe objects they cannot accurately grasp.

This suggests that these two visual pathways, although complimentary, are specialised for different things, one for identifying objects, and the other for working out where they are and how to manipulate them.

The different function of the two pathways can also be demonstrated in healthy people as well.

You may recognise the visual illusion on the left, sometimes called the Titchener or Ebbinghaus illusion. The two circles in the middle are actually the same size, but look different due to their context.

Researchers have created a graspable version of the illusion by putting hoops on a flat surface.

When they’ve measured how people adjust their fingers to pick up the middle circles, they find that we don’t over or underestimate the size. Our fingers are always perfectly adjusted to the actual size.

In other words, it seems that while our perception is fooled by the illusion, our actions aren’t, showing how the specialisation of each visual stream can be seen in everyone.

There’s now a minor cottage industry of research attempting to understand exactly what influences the effect.

UPDATE: “All in the Mind has been honoured with the Grand Award at 2008 New York Radio festivals for best entry across all categories, as well as a Gold World Medal in the Health / Medical category”. – I’m sure it won’t come as a surprise to most Mind Hacks readers but fantastic to have it recognised by the non-initiated!

Link to AITM on out-of-body experiences and other tricks of consciousness.

A scene from a thousand horror movies, retold in the medical literature, with an additional lesson about the correct use of cerebral perfusion and angiography in diagnosing the brain dead patient.

Presumably, learnt shortly after the doctors had stopped screaming.

I love the use of the phrase “the situation became confusing”, just after the dead guy starts moving again.

Unusual movements, “spontaneous” breathing, and unclear cerebral vessels sonography in a brain-dead patient: a case report.

Bohatyrewicz R, Walecka A, Bohatyrewicz A, Zukowski M, Kepiński S, Marzec-Lewenstein E, Sawicki M, Kordowski J.

Transplant Proc. 2007 Nov;39(9):2707-8.

A patient with a brain injury fulfilled all clinical criteria for brainstem death diagnosis. Two standard sets of tests were performed; according to Polish regulations, the patient could be declared brain dead. However, shortly after the completion of the tests and before the final brain death declaration, 6 triggered “assisted” breaths/min were noticed. After careful analysis of the ventilator settings, it was concluded that low trigger sensitivity and airway pressure oscillations during heart contractions were the reasons.

Additionally, a few minutes later, spontaneous jerking movements of lower limbs and clonic movements of neck muscles secondary to painful stimuli were noticed. The situation became confusing; therefore, cerebral Doppler sonography was performed, showing circulatory arrest in both of the internal carotid, middle cerebral, and left vertebral arteries. The basilar artery was not visualized. Forward flow with increased pulsatility was recorded in extracranial and intracranial segments of the right vertebral artery. Cerebral circulatory arrest was still uncertain; therefore, the diagnostic procedures were completed with conventional cerebral angiography, which showed a lack of cerebral blood flow.

Finally, the patient was declared brain dead; kidneys and bones were harvested. Cardiogenic oscillations associated with incorrect low ventilator trigger settings may falsely suggest persistence of breathing efforts in a brain-dead patient. In the case of any unusual events during brain death diagnosis, cerebral perfusion tests should be performed with cerebral angiography as the “gold standard.”

Link to PubMed entry.