Why are men better at darts and
women better at chatting? How do
we recognise fear in others? What
is memory made of? In the second
part of our series, we look at new
discoveries about the human brain
THINK about it. Every word in this sentence is causing wave upon wave of electrical storms to rage through your brain. The very act of reading and thinking, such a uniquely human feature, is generating intricate patterns of electrical and chemical activity that are so complex, yet so transient, that they seem beyond the comprehension of the brain itself. Scientists believe this is about to change dramatically, however, now that brain scanners have allowed them to view the vast landscape of the human mind.
What do we really know about the workings of our own brains? The answer is that we understand a tiny fraction of what the brain can do, but the potential for finding out more is enormous. This year has seen a remarkable variety of research reports elucidating different aspects of brain function. Scientists have identified, for instance, a region of the brain involved in recognising fear in the faces of others; they have come closer to understanding the cerebral abnormalities that seem to be associated with dyslexia and other reading difficulties; and they have examined with some success an age-old debate centred around the battle of the sexes - do men and women think differently?
The apparent differences between the capacities of men and women have been apparent ever since psychologists devised problem-solving tests to assess mental performance. Women are generally better at rapidly matching objects or items in their field of vision, a skill called "perceptual speed". They are more verbally fluent, performing better than men in tests involving words. They are also better at arithmetical skills and recalling landmarks from a route, as well as being better at precision manual tasks, like putting different shaped pegs into holes on a board.
Men are good at spatial tasks, such as imagining an object being rotated in space or navigating round an obstacle course. They generally have better mathematical skills that involve reasoning, and are better at what psychologists call "target-directed motor skills" - but what the rest of us call "playing darts".
Many people would argue that these attributes are due to upbringing, not to innate biological differences in the brain. Upbringing and the way little boys and girls are treated undoubtedly play their part, but this is not the whole story. Even three-year-old boys are better than girls of the same age at target skills, so conditioning - in the form of the "male" and "female" sports played in childhood - does not appear to account for the sex differences in the targeting skills of young adults.
Doreen Kimura, professor of psychology at the University of Western Ontario, believes the differences between male and female brains are real. "It has been fashionable to insist that these differences are minimal, the consequence of variations in experience during development. The bulk of the evidence suggests, however, that the effects of sex hormones on brain organisation occur so early in life that, from the start, the environment is acting on differently wired brains in girls and boys.''
Differences in the way the two sexes process language has been an especially interesting area for brain researchers to investigate, particularly since women tend to "outverbalise" men. It has been known, for instance, that aphasia - speech disorders - are more common in men than in women when the left side of the brain is damaged, say in an accident or after a stroke. Yet Professor Kimura has found that women are more likely than men to suffer aphasia when the front part of the brain is damaged. This clearly indicates that the brains of men and women are organised differently in the way they process speech.
Earlier this year, this sort of research received a dramatic boost with publication of a study by a team of scientists led by Bennett and Sally Shaywitz, a husband-and-wife team at Yale University. The researchers took 19 men and 19 women, and placed them in a magnetic resonance imaging scanner that could detect minor changes in blood flow to different parts of their brains while they were asked to match rhyming words. What they found was that many of the women used the right side of their brains more than the men for this very specific task.
Another well-known feature of male and female minds is being able to determine the emotion in another person's face. How the brain deals with facial expressions is important because, from a very early age, we recognise the value of reading correctly whether a face is angry, say, or happy.
Anecdotal evidence abounds of men being incapable of seeing that something has upset their partner until they find themselves swimming in a flood of tears. On a more experimental basis, it does seem true that women are far better at determining emotions by facial expressions. In one experiment, women correctly identified sad faces among a set of photographs of men and women nine times out of 10. Men matched that performance only when they had to assess the sadness of male facial expressions. They were significantly worse when it came to assessing sadness in women's faces, getting just seven out of 10 correct.
Ruben Gur, professor of neuropsychology at the University of Pennsylvania in Philadelphia, has studied emotional differences in men and women, again with the help of the ubiquitous brain scanner. He took 61 volunteers under 45 years of age, 37 men and 24 women. He measured how fast certain areas of their brains were using up blood glucose when they were resting, but awake. Men were more likely to have activity in the temporal limbic region of the brain, which in evolutionary terms is very old because we share it with most other animals, including reptiles; women were more active in the cingulate region, which is far more recent, being more developed in "higher" animals such as the primates and particularly well-developed in humans.
Professor Gur concluded that men tend to deal with emotions on a more basic level, much like a crocodile lashing out aggressively, whereas women "sit down and talk about it" - akin, perhaps to a chattering monkey. "Men often express their emotions through overt aggression. Women deal with theirs more symbolically by talking about their feelings more than men, who often sulk and say 'What's there to talk about?'," Professor Gur says.
Intriguing though the differences are between the brains of men and women, rarer insights are gained by studying patients with unusual mental problems. One example is a 30-year-old woman of normal intelligence who suffers from Urbach-Wiethe disease, an inherited condition that causes the almost complete destruction of a part of the brain called the amygdala - roughly the size and shape of an almond, buried deep in the brain's temporal lobes. Its precise function has long puzzled scientists, which is why this patient was so interesting to them.
Researchers at the University of Iowa and the Salk Institute for Biological Studies at La Jolla, California, were especially intrigued by how this woman perceived emotion in the faces of others. She had no trouble recognising the faces of people she knew, but she had enormous problems seeing any signs of overt fear, anger or surprise in facial expressions. A dozen other brain-damaged people of similar IQ did not have this problem. The researchers concluded that facial recognition by the brain and recognition of facial emotion are not just functionally distinct, but carried out by anatomically different regions of the brain.
"In so far as expressions of a single, basic emotion are concerned, the human amygdala's role appears to be quite specific to recognition of fear," the scientists reported. "From our results, the amygdala appears to be necessary both to recognise the basic emotion of fear in facial expressions, and to recognise many of the blends of multiple emotions that the human face can signal."
Facial recognition is important to the study of the brain because it appears to be so deeply programmed into all of us, as would be expected in a social species that relies on the face to tell individuals apart. Research in this field also helps in the understanding of the mentally ill. Autistic children, for example, do not pay much attention to the facial expressions of others, and part of the problem seems to be that they cannot tell when someone is looking directly at them. Some researchers believe the amygdala may be involved, because another patient with a damaged amygdala had the same difficulty.
Another fruitful line of enquiry for brain researchers and their scanners is to compare gifted people with the general public. This has often highlighted differences in the activity of the left and right hemispheres of the brain. A research team from Dusseldorf's Heinrich-Heine University in Germany, for instance, scanned 30 musicians and 30 non-musicians and found that the music makers had clearly ''lateralised'' left sides of their brains. In professional musicians, the planum temporale - the region of the cortex that processes sound signals - is far larger on the left side than on the right. The difference was particularly distinct for musicians with perfect pitch, the natural gift of hitting the right note without the need for any reference note.
Previous research on musical ability and brain activity indicated that it was the right side that was involved, as indeed it is in musician and non-musician alike. But what appears to happen in professional musicians is that the left side - associated with ''higher'' function such as language - is brought into play. One brain scanner study of music students found that, when they started their course, the right side was mainly activated. When they had completed their course three years later, their left side also came into play when they analysed what they heard.
This exemplifies what is probably the most important and far-reaching finding of current brain research. As well as being a highly complex structure capable of an almost infinite array of electrical and chemical activity, the brain possesses the powerful attribute of mental plasticity: it can make and break nerve connections over a period of intellectual training - anything from remembering a route home to learning a Mozart symphony.
Steven Rose, professor of biology at the Open University, has for many years specialised in understanding this making and breaking of nerve cell connections and the role it plays in memory. It is an idea that goes back at least to 1949 when Donald Hebb, a Canadian psychologist, suggested that memories can be stored in the brain by simply altering the strength of nerve cell connections. These, as the memory of last week's Sunday Review feature will recall, exist in such great numbers that it would take 32 million years to count them all at the rate of one a second.
Professor Rose is just beginning a collaborative research effort, with his Open University colleague Stephen Swithenby, on a new form of brain scanner that monitors the tiny magnetic fields generated by nerve cells as they transmit electrical impulses. This sort of research on volunteers has its limitations, however, principally because there are limits to the experiments that can be done on humans. Professor Rose, however, uses an alternative to humans to build up an impressive picture of the memory process at work. His experimental subjects are newborn chicks, who learn memories almost from the moment they hatch.
''Young chicks are good to work with because they have to learn about their environment very fast. If they don't, they don't survive.'' Rose can train the chicks in certain things, such as the memory of pecking on a small, bitter-tasting bead. He then investigates the changes that have taken place in their brains. He has found that memories are made of new nerve cell connections. ''What we've been able to uncover is a cascade of biochemical processes that go on in specific regions of the chick's brain, which culminate in changing the connections between cells.''
The precise detail of how a memory is made could be explained, says Professor Rose, by cell adhesion molecules acting as a bridge between two nerve cells. These molecules can temporarily lose their ''stickiness'' in a complex set of reactions involving sensory inputs from eyes, ears or whatever, and the presence of sugar molecules that behave as the physical glue.
Professor Rose says that a nerve cell connection - a synapse - can move fluently under the influence of the memory-forming process. The cell adhesion molecules exist in an embryonic form which is not very sticky, and a mature form which is. ''What we think happens during the process of memory formation is that the cell adhesion molecules temporarily revert to their embryonic form; the sugar molecules come off and they lose their stickiness, which enables the synapse to move fluently.''
This research underpins what brain researchers are frequently at pains to point out when asked to compare the brain with a computer: the two are so different the comparison is next to useless. A computer memory, for instance, is a fixed entity, whereas the memories locked away in the brain are dynamic and ''alive''.
Current research highlights just how different the brain and computer are when dealing with the processing, storage and retrieval of information. Steven Rose believes the key to a greater understanding of the human mind will be studies into the brain's ability to store and retrieve data. ''Memory research offers the best chance there is of discovering the translation rules between mind, brain and behaviour, subjectivity and objectivity. It could be the Rosetta Stone for the neurosciences.'' !Reuse content