Science of the bloody brain

One of Mosso’s experiments. Each of the four traces on the right compares brain blood flow (red) and pulsations in the feet (black) simultaneously, during 1)resting 2)listening to the clock and church bells 3)remembering whether Ave Maria should have been said and 4)’8×12′?

Luigi Cane literally had a hole in his head. A brick had unforgivingly fallen on the back of it, smashing a section of his skull like a spoon knocking the shell off the top of a hard-boiled egg. And so, after surgery, part of the surface of his brain was left precariously unprotected except for a layer of skin. Peering through this accidental window into his head, Dr. Angelo Mosso was able to measure the pulsations of the brain’s blood supply. Cane sat in Mosso’s lab with pressure gauges strapped around his feet and a handmade instrument resting delicately on the skin over his vulnerable brain. This was to be the world première of neuroimaging.

Angelo Mosso, a 19th century physiologist and first brain imager

“What is 27 times 13?” Mosso inquired. Cane thought deeply and silently while the various contraptions simultaneously showed his feet shrinking while his brain swelled with blood flow. This experiment was the first to reveal that when our mental ‘cogs’ turn, a boost of blood is directed to the brain. Mosso confirmed this in individuals with intact skulls with what was essentially a wobble-board bed. When people lying down on the balance thought about tricky or even particularly emotional questions, it would tip down towards the head end with the weight of the extra blood.

The brain is an extremely greedy part of the body when it comes to blood. While it only makes up about a fiftieth of the body’s mass, it consumes up to a fifth of the total energy and oxygen carried in the bloodstream. Charles Roy and Charles Sherrington later proved that the blood rushing to the head was actually being diverted specifically to the parts that were most active – like a bonus for the busiest brain cells. Over twelve decades later, neuroscientists are still using this same principle to observe brain activity and the accompanying ‘rush of blood’ to the head.

The brain imaging technique functional magnetic resonance imaging (fMRI) works on the principal that deoxygenated haemoglobin (the protein that carries oxygen in red blood cells) has magnetic properties. In essence, fMRI can measure how well-oxygenated or deoxygenated different parts of the brain get when the person in the scanner performs a task, for example reading, writing, or thinking about chocolate. But information collected from this kind of experiment needs to be handled very carefully.

Computer-enhanced fMRI scan of a person who has been asked to look at faces. The image shows increased blood flow in the part of the visual cortex that recognizes faces.

Firstly, fMRI is not a direct measure of brain activity per se; rather, it’s the triggered oxygenated blood flow response to brain activity. Secondly, no one really knows what a larger blood flow response means, especially in parts of the brain that have several jobs. Lots of blood in a specific part of the brain while doing sums might mean that a person can do sums easily because their blood supply is so efficient. Alternatively, it could be interpreted as suggesting that person struggles with mental arithmetic and needs more blood in their head to cope. Thirdly, fMRI data needs to be stringently tested to avoid seeing activity that isn’t there. Researchers at the University of California found that using different statistical tests they could see a blood flow response in the brain of a dead salmon while it was looking at different human faces – and won an IgNobel Prize for highlighting the dangers of shoddy stats.

With all this to bear in mind, it’s perhaps unsurprising that poorly carried out fMRI experiments have been dubbed the modern phrenology – the practice of comparing measurements of peoples’ skulls to infer personality traits. What is perhaps more surprising, though, is that despite the speculations on the validity and accuracy of fMRI, it is being used for things besides its more traditional remit. ‘No Lie MRI’ is a company in the U.S. that advertises the use of brain imaging to detect liars or untrustworthy individuals, whether they be potential politicians, investments or romantic interests. Brain imaging techniques including fMRI have even controversially been used as evidence in Indian courts of law.

Example of fMRI responses to painful heat to the forehead in a cohort of 12 subjects. ACC, anterior cingulate cortex; PCC, posterior cingulate cortex (Moulton et al., unpublished observations). Borsook et al. Molecular Pain 2007 3:25

There are, however, other emerging uses for fMRI that may improve its reputation. By watching live feedback of the blood flow going to the anterior cingulate and insula, two pain centres deep within the brain, sufferers of chronic pain can consciously train these parts of the brain to receive more blood. Christopher deCharms and his colleagues at Omneuron have found that people who were given the real, live feedback from their insula and cingulate and successfully learnt to train the blood flow within these parts said they experienced less pain than usual. Conversely, people unwittingly shown a dummy feedback (random fluctuations or blood flow levels from an unrelated part of the brain) didn’t report any substantial pain relief.

Brain imaging techniques that rely on measuring blood flow around the brain should be carefully interpreted; fMRI is heavily-used in research and is still fashionable in brain research. Technology has come on a massively long way since the days of wobble boards, so we should probably count ourselves lucky that we don’t need a hole in our heads to unlock the further mysteries of the blood in our brains.

Post by Natasha Bray


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