8 February 2010

Ability to navigate may be linked to genes

by Kate Melville

Human, animals and even fish routinely reorient themselves using landmarks and mentally visualizing the geometry of their surroundings. Now, according to new research described in the Proceedings of the National Academy of Sciences, it appears there may also be a genetic component that plays a part in our ability to navigate the world.

The study, by Barbara Landau at The Johns Hopkins University, involved people with a rare genetic disorder known as Williams syndrome. The syndrome is caused when a small amount of genetic material is missing from one human chromosome. People with Williams syndrome are extremely social and verbally adept, but have difficulty with tasks such as assembling simple puzzles, copying basic patterns and navigating their bodies through the physical world. Williams syndrome affects one in 7,500 people.

In the study, Landau's team challenged people with Williams syndrome to watch while someone hid an object beneath a small cloth flap in one corner of a small rectangular room with four solid black walls that had no landmarks. Subjects were then blindfolded and spun around for about 10 seconds to disorient them. Once the blindfold was taken off, the subjects were asked to find the hidden object. According to Landau, the people with Williams syndrome searched the four corners randomly; indicating that their ability to mentally visualize the layout of the room and quickly find which corner held the hidden object is severely impaired.

"They searched the room for the hidden object randomly, as if they had never before seen the overall geometry of the room or the lengths of the walls and their geometric - left and right - relation to each other," Landau explained. "If they could imagine the overall shape of the room's layout - that there are four walls, two of them long and two of them short and that the toy was hidden in a corner that has a short wall on the right and the long wall on the left - then they should have guessed that one of the two 'geometrically equivalent corners' was the right place. This is what typically developing humans do, as early as 18 months of age."

Landau says that her work is the first evidence from human studies of a link between the missing genes and the system that we use to reorient ourselves in space. "Although we are quite far from understanding the links between the specific genes that are missing in Williams syndrome and the behavior they show, such as failure to reorient, it is clear that the missing genes ultimately have some effect on the brain," she said. "Our evidence is the first to directly show a substantial deficit in this reorientation system that is caused by missing genes in humans."

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Source: Johns Hopkins University