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Thursday, January 27, 2011
Transsexual differences caught on brain scan
Differences in the brain's white matter that clash with a person's genetic sex may hold the key to identifying transsexual people before puberty. Doctors could use this information to make a case for delaying puberty to improve the success of a sex change later.
Medics are keen to find concrete physical evidence to help those children who feel they are trapped in the body of the opposite sex. One key brain region involved is the BSTc, an area of grey matter. But the region is too small to scan in a living person so differences have only been picked up at post-mortem.
Antonio Guillamon's team at the National University of Distance Education in Madrid, Spain, think they have found a better way to spot a transsexual brain. In a study due to be published next month, the team ran MRI scans on the brains of 18 female-to-male transsexual people who'd had no treatment and compared them with those of 24 males and 19 females.
They found significant differences between male and female brains in four regions of white matter – and the female-to-male transsexual people had white matter in these regions that resembled a male brain (Journal of Psychiatric Research, DOI: 10.1016/j.jpsychires.2010.05.006). "It's the first time it has been shown that the brains of female-to-male transsexual people are masculinised," Guillamon says.
In a separate study, the team used the same technique to compare white matter in 18 male-to-female transsexual people with that in 19 males and 19 females. Surprisingly, in each transsexual person's brain the structure of the white matter in the four regions was halfway between that of the males and females (Journal of Psychiatric Research, DOI: 10.1016/j.jpsychires.2010.11.007). "Their brains are not completely masculinised and not completely feminised, but they still feel female," says Guillamon.
Guillamon isn't sure whether the four regions are at all associated with notions of gender, but Ivanka Savic-Berglund at the Karolinska Institute in Stockholm, Sweden, thinks they might be. One of the four regions – the superior longitudinal fascicle – is particularly interesting, she says. "It connects the parietal lobe [involved in sensory processing] and frontal lobe [involved in planning movement] and may have implications in body perception."
A 2010 study of 121 transgender people found that 38 per cent realised they had gender variance by age 5. White matter differences could provide independent confirmation that such children might benefit from treatment to delay puberty.
A study by Sean Deoni's team at King's College London suggests it may soon be possible to look for these differences in such children. Deoni's team adapted an MRI scanner to be as quiet as possible so it could be used to monitor the development of white matter in sleeping infants. Using new image analysis software they could track when and where myelin – the neuron covering that makes white matter white – was laid down (Journal of Neuroscience, vol 31, p 784). Although the sample was too small to identify any gender differences in development, Deoni expects to see differences developing in the brain "by 2 or 3 years of age".
Guillamon thinks such scans may not help in all cases. "Research has shown that white matter matures during the first 20 to 30 years of life," he says. "People may experience early or late onset of transsexuality and we don't know what causes this difference."
Virtual blood and smoke give gore to student surgeons
SPILT blood and burning flesh can now be modelled accurately. But you won't find the software in a gory shoot-'em-up video game, at least not yet. Instead it will used to make virtual surgery look more lifelike.
Like airline pilots, surgeons practise their trade using simulators. For keyhole surgery routines they use a dummy torso with mock organs and a variety of grasping, cutting and cauterising tools. Transducers in the organs sense the forces exerted by the instruments and feed them to a PC, which screens a virtual representation of how real organs would respond.
But merely simulating how the organs respond to the tools and move against each other in real time takes up most of a top-end PC's number-crunching power, says Suvranu De, an engineer at Rensselaer Polytechnic Institute in Troy, New York. That means other important aspects of surgery have to go unmodelled, reducing the realism of the simulation.
"Intra-abdominal tissue has a very high density of blood vessels. When a cauterising device cuts it, copious amounts of smoke are generated and bleeding may occur. These effects are hard to incorporate in a simulation," says De. That's because such simulations would involve solving fluid dynamics equations every time the blood or smoke moves, something existing technology takes several hours to do.
To get around this problem, De's team has developed a technique that instead overlays pre-programmed visual effects onto the simulations.
First, they took sample video footage from real keyhole surgery showing how smoke can obscure the surgeon's view. These clips were of both the dense smoke coming from the tip of the cauterising tool and the wispy smoke further away.
They stored these sequences and wrote an algorithm that enables the PC's graphics processor to call them up whenever the cauterising tool is used. The software updates the overlaid images at a rate of 30 frames per second - fast enough to give an interactive feel to the simulation. The smoke density in each image depends upon the length of time the tool is used as well as distance from the cauterised site.
To simulate the degree of bleeding, another algorithm consults a database of the vascular density at the point of interest in the body. It then estimates the likely bleeding rate, depending on the depth of the surgeon's cut, and brings up animation sequences of the appropriate amount of pooling blood to overlay on the simulation.
The team hopes to refine the software further to improve its realism - and could even transfer it to video games. "This is a very clever way to do it," says Vincent Luboz at Imperial College London, who works on surgery simulators. But he adds that the technique is more suited to general training than to rehearsing an operation on a particular patient.
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