Month: June 2008

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.

Over the last few months, the soul searching over the shortcomings of fMRI brain scanning has escaped the backrooms of imaging labs and has hit the mainstream.

Numerous articles in hard hitting publications have questioned some common assumptions behind the technology, suggesting a backlash against the bright lights of brain scanning is in full swing.

There are two strands to this debate, and both stem from the fact that the technology and conceptual issues of brain imaging are incredibly complex.

To fully understand what happens during a brain imaging experiment you need to be able to grasp quantum physics at one end, to philosophy of mind at the other, while travelling through a sea of statistics, neurophysiology and psychology. Needless to say, very few, if any scientists can do this on their own.

So the first strand involves how brain imaging experiments are reported in the media. Under the sheer weight of conceptual strain, journalists panic, and do this: “Brain’s adventure centre located”.

It’s a story published this morning on the BBC News website based on an interesting fMRI study looking at brain activity associated with participants choosing a novel option in a simple gambling task. But out of the four words of the headline, only the first is accurate.

And this leads to the second strand of the debate, which, until recently, has been largely conducted away from the media’s gaze, amongst the people doing cognitive science themselves.

It starts with this simple question: what is fMRI measuring?

When we talk about imaging experiments, we usually say it measures ‘brain activity’, but you may be surprised to know that no-one’s really sure what this actually means.

Neuroscientist Nikos Logothetis published an important paper in Nature a couple of weeks ago explaining exactly what we know so far about the link between what brain scans measure and what the brain is actually doing.

It’s very wide-ranging and includes lots of grit-your-teeth hardcore neurophysiology, but is, I think, essential reading if you’re neuroscientifically inclined.

It focuses on BOLD, the signal that reflects the ratio of oxygenated and deoxygenated blood measured by fMRI, and the fact that it can be altered by a huge range of different biological process and neural firing patterns.

One of the main points of the paper is that the brain is not simply an array of tiny localised processors, but it is more like an an ecosystem of communication.

Activity can result from sending more signals, trying to send less, or, from what seems to be particularly important – maintaining a balance of excitation and inhibition.

Furthermore, it seems that a great deal of neural activity is not from neurons that might be directly involved in a task, but from ‘neuromodulation’ – general processes of management and coordination, often linked to attention. This can wax and wane, can spread like ripples and can occur in all sorts of non-linear ways that makes interpretation difficult.

What this means is that brain imaging experiments need to be carefully designed to control for these effects, but this entirely depends on our understanding of the effects themselves.

In other words, our understanding of what brain scanning data tells us evolves over time. A study conducted ten years ago might mean something different now.

An article in Science, published in the same week as Logothetis’ paper, reports on new statistical methods for interpreting imaging data, a different issue again.

The latest edition of The New Atlantis has an article that attempts to come to grips with some of the philosophical aspects of brain imaging experiments, in terms of the conceptual limits in inferring mental states from biological changes.

I have to say, it’s a bit miscued in places, assuming that brain imaging relies on ideas about brain modularity (which it doesn’t) and seemingly confusing it with the notion of pure insertion, and suggesting some rather strange notions about mental causation, but it has many good points and is worth a read.

It’s important that these sorts of issues come to light, because it hopefully heralds a time of increased caution in our interpretation of brain scans – and that goes for scientists, the media and the general public.

This is essential, because this data is starting to be used, literally, in life or death decisions.

The same issue of The New Atlantis has an article on neuroimaging that discusses the ethical dilemmas in applying this imperfect technology to legal decisions concerning capital punishment.

Link to Logothetis on ‘What we can do and what we cannot do with fMRI’.
Link to Science article ‘Growing pains for fMRI’.
Link to New Atlantis on ‘The Limits of Neuro-Talk’.
Link to New Atlantis on Neuroimaging and Capital Punishment.

Michael Gazzaniga, one of the founding fathers of cognitive neuroscience and a pioneer of ‘split brain’ research, is interviewed on this week’s ABC All in the Mind where he talks about the use and abuse of ‘left brain – right brain’ metaphors and how our understanding of free will is impacting on the law.

Gazzaniga was a student of Roger Sperry, who won a Nobel prize for his work on ‘split-brain patients’, people who had the two cortical hemispheres of the brain functional separated by neurosurgery to cut the corpus callosum in an attempt to treat otherwise untreatable epilepsy.

One of the amazing things was that while the people didn’t feel any different, it was easy to demonstrate that the each hemisphere processed things in quite different ways and each was, to a certain extent, independently conscious.

The interview discusses some of this early research, and asks how much of the popular ‘left brain – right brain’ rhetoric that gets thrown around actually stands up to scientific scrutiny. I think you can guess, but it’s good hearing it from the man himself.

Gazzaniga also talks about one of his other interests – neuroethics, and particularly the effect that a neuroscientific understanding of free will is having on our concepts of legal responsibility.

I was interested to read that US judges can now take courses in neuroscience to help them makes sense of the sometimes counter-intuitive findings in cognitive science.

As it happens, Gazzaniga’s new book Human: The Science Behind What Makes Us Unique is published today. If you want a taster an Edge article by Gazzaniga from a few months ago seems to be taken from it.

The AITM Blog also has some bonus audio of Gazzaniga discussing his experience of being on George Bush’s bioethics council when the President was vetoing stem cell cloning.

Link to AITM interview with Michael Gazzaniga.