Stripping Down Science (23 page)

And Jupiter? Interestingly, the answer to this puzzle probably lies outside our own solar system. In recent years, astronomers have discovered Jupiter-sized planets orbiting distant stars but,
in many cases, these so-called ‘hot Jupiters' are so close to their parent stars that they couldn't possibly have formed in that position, meaning they must have migrated there. Researchers believe this happens because the planets pick up progressively more material lying between them and the star, causing them to be drawn inwards towards the centre of the solar system. Luckily for us, our own Jupiter didn't move in too far, or we would have been on a collision course with a juggernaut.

FACT BOX

Clever way to spot alien planets

Because cosmology and space science tend to happen on time scales that are measured in billions of years, it can sometimes be easier to answer questions about the past and future of our own solar system by looking at a different one that happens to be the age you're interested in. But in 2003, the International Astronomical Union, meeting in Australia, estimated that
there are at least 70 sextillion (seven followed by 22 zeros!) stars out there in the universe, and at least 200 billion just in our own Milky Way Galaxy. So how do we know which ones to look at, especially if we want one with planets we can study?

Previously, it was a painstaking task of watching stars carefully to see if they wobbled a tiny bit or their light altered slightly, which could indicate a planet was in orbit. But in 2009 scientists made a breakthrough that should speed up the whole process. Garik Israelian, from the University of San Fernando de La Laguna in Tenerife,
⁷⁶
surveyed more than 500 stars (of the celestial variety), 70 of which have already been confirmed as having planets in orbit around them. By analysing the spectrum of light from each star, it was possible to measure, using a technique discovered in the 1800s by none other than Robert Bunsen, what chemical elements were present.

When the data from these stars were
compared and factors such as age were taken into account, a surprising trend emerged. The majority of the stars showed evidence for the presence of the element lithium on their surfaces, but the 70 stars
known
to have planets orbiting them, our own sun included, had hardly any.

Israelian thinks that the presence of planets somehow stirs up the substance of the star, pulling any lithium on the star's surface into the hot interior where it is consumed. How exactly this happens no one yet knows, but the key point is that, by looking for a lack of lithium in the spectral signature coming from a star, space scientists now have a shortcut way to find new planets much more quickly – so watch out, ET, here we come!

According to Mark Twain in
Roughing It
, JRR Tolkien in
The Lord of the Rings
, and various picture house hits including
The Blair Witch Project
and
The Flight of the Phoenix
, people are prone to wander around in circles when they get lost – and when they do it on camera, they also inevitably wind up with an Oscar and a box office blockbuster!

Previously, science has had very little to say about this claim, which has been dismissed by many as mere Hollywood hype. But now scientists have put this potential myth to the test and, it turns out, this is one circular argument that does have some facts to back it up.

Jan Souman, a researcher at the Max Planck Institute in Tubingen, Germany,
⁷⁷
unleashed six walkers in unfamiliar forest terrain and told them to walk in a straight line for several hours.
He also repeated the process with three subjects who were asked to walk in the Sahara Desert. The progress of all of the walkers was charted using a GPS system to follow where they went. In both geographies, the walkers went off course whenever they couldn't see the sun (or the moon, in the case of one nocturnal Saharan rambler). Under these circumstances, the routes they took quickly became circular, with the walkers frequently crossing and re-crossing their own paths.

But why? Haven't we got a sense of direction? One possibility is that this happens because, just as we have a tendency to favour one hand or one eye over the other, in some people there may also be an innate tendency to turn in one direction. This could also occur for biomechanical reasons, such as having one leg longer or stronger than the other.

To find out whether this was the case, Souman also carried out a series of additional walking exercises on an airstrip (fortunately, one that wasn't in use). With the subjects blindfolded, he told them to keep walking in a straight line in a certain direction indicated to them beforehand. To check for the effects of any biomechanical
issues, he also measured muscle power, X-rayed the legs of one individual to accurately gauge their lengths (they differed by less than one millimetre) and repeated the experiment after altering the heights of the soles of the subjects' shoes to make their legs different lengths.

The results showed that there was no correlation between the mean direction in which the subjects turned when they walked blindfolded and any mechanical asymmetry – the subjects just ended up following random trajectories punctuated by small circles which were often small enough to fit inside a basketball court. Interestingly, this meant that the greatest as-the-crow-flies distance any of the subjects got from their starting points during over 50 minutes of blindfolded walking was just 100 metres. Helpfully, this suggests that if a person was lost and blundering about in dense forest without access to any visual landmarks, concentrating a search within the area in which a missing person was last seen would be the best strategy for rescuers.

Why does this happen? Souman thinks that people veer off course in the absence of a visual guidance cue, like the sun, because of ‘neurological noise' – small errors in the processing of the motor,
sensory and balance systems in the brain, which alter the subjective sense of what is ‘straight'. Quite literally, and with every step, a random error is added to the subjective ‘straight ahead', causing it to drift off true. When these deviations become large, people often end up walking in circles, regardless of whether they have a good ‘sense of direction' or not.

The moral of this story is, when lost in the forest – or the Sahara – follow the sun or the moon, or stay put!

FACT BOX

Human navigation

Although Jan Souman's study suggests that we have an innate tendency to become lost, many people nonetheless claim to have a strong sense of direction and can tell which way they ought to be going. But is it real and can it be relied upon?

This was looked into by a Manchester University scientist, Robin Baker, in a study he
published in 1980.
⁷⁸
He blindfolded 64 student volunteers and drove them along a tortuous route to a series of remote locations up to 52 kilometres from the university. At each location, the volunteers were asked – without removing the blindfold – to indicate the compass direction in which they thought the university lay. In each case, the results were strongly correlated with the real direction, suggesting that the subjects innately appeared to know where home was situated, despite none of them being able to account for how they arrived at their directional decisions.

To find out whether they might be tapping into the earth's magnetic field as a form of cognitive compass, 15 of the subjects had bar magnets strapped to their heads. The rest of the group were given identical non-magnetic pieces of metal, but no subject knew whether they had a real magnet or not. The results from the magnet wearers were all well off-course compared with their control colleagues,
suggesting that magnetic cues could be playing a part in helping to drive our sense of direction. As yet though, no one has found what underlies this ability, or even which part of the brain, head or neck is responsible.

But if we have an inbuilt direction-finding system, why do people wander in circles, as Souman says? Probably because, as humans, we have evolved to set higher store by another, more dominant sense. Over a third of the human brain is devoted to processing what we see so, not surprisingly, we tend to focus on what our eyes are telling us and prioritise this over other subtle cues and signals coming in from the world around us.

So how
do
we find our way around, or recall the route we took across town, or retrace our steps to find the restaurant where we left the umbrella at lunchtime? Well, scientists have discovered in recent years that the brain uses a neurological grid system resembling a three-dimensional radar screen with us plotted in the middle of it. The grid is located in a part of the brain's temporal lobe called the
entorhinal cortex and it consists of an array of interconnected nerve cells linked up to form a series of equilateral triangles. When a person moves, their blip on the radar screen is tracked by altering the firing activity of the nerve cells that form the region of the grid representing the part of the world in which they are standing. In this way, the person knows where they are in their environment at any given time.

The first insights into the workings of this system were provided by making recordings from individual nerve cells in the brains of rats and mice as they foraged for food. Scientists realised that these animals were finding their way around by orientating their movements relative to various landmarks that were also plotted on this neurological grid. If those landmarks moved – for instance, if a rat's cage was turned 180 degrees – then the grid would reconfigure to reflect the new locations of the landmarks relative to each other.

Of course, it's not practical or ethical to implant electrodes into the heads of humans for the purposes of monitoring movements.
However, it is possible to use brain scanners, and a researcher at University College London, Christian Doeller,
⁷⁹
has recently developed a computer-based system to confirm that the human navigational system seems to work the same way as a rodent's. Forty-two human volunteers were brain-scanned as they explored a 3D environment shown to them through a virtual reality headset. Incredibly, the brain scanner was able to pick up in the subjects' entorhinal cortices the same neurological signature that would be expected based on the workings of the equivalent region of a rat's brain.

Thankfully, the similarity doesn't appear to extend to experiencing a compulsion to dive down the nearest sewer, although some people do rummage in dustbins – perhaps we now know why!

It's commonly claimed that for women, pregnancy and childbirth shrink your brain and erode your memory. In fact, anyone who reads just a fraction of what's penned in the birthing literature about what some are calling ‘placental brain drain' would be excused for thinking they should be checking themselves into a dementia clinic rather than a maternity hospital! But is there really any reliable evidence to back up these claims of baby-induced intellectual meltdown? Surprisingly, or perhaps not, the answer is actually ‘no', and recent research is now suggesting that the whole thing may just be an over-gestated myth well past its due-by date.

So how were these ill-founded claims of compromised cognition conceived in the first place, and how have they managed to implant themselves in our psyche? It probably all stems from the fact that the majority of the studies that have looked at women's brains during pregnancy
have taken small groups of pregnant women and compared them with other small groups of non-pregnant ‘control' women to see how the cognitive abilities of each match up.

The obvious problem with this sort of study design is that the one thing you're seeking to find out – whether the brainpower of the pregnant person has changed – isn't being tested at all, because the pregnant subjects were invariably not assessed before they became pregnant to find out what was ‘normal' for them. At the same time, many of the studies relied on participants self-reporting symptoms of memory loss or poor concentration. And because pregnancy is stressful at times, and pregnant women have heard the claims that their IQ ought to be dropping faster than a faulty facelift, so-called ‘recall bias' kicks in and a self-diagnosis of borderline idiocy is made.