Lefties--or at least relatives of lefties--may be better than right-handed people at remembering events, according to a new study.
Since the mid-1980s, scientists have known that the two brain hemispheres of left-handers are more strongly connected than those of right-handers. Cross-talk between the hemispheres may be important for remembering specific events, called episodic memory, so psychologists Stephen Christman and Ruth Propper of the University of Toledo, Ohio, reasoned that lefties and righties might differ in episodic memory skills. If you're not a southpaw, don't despair: The two believe that factual memory--things people know but don't necessarily remember learning--does not rely on interhemisphere interaction.
To test their theory, Christman and Propper asked 62 subjects to watch a series of 55 words flashed on a computer screen. Several minutes after the task, subjects were asked to write down the words. When errors were subtracted from correct answers, those with left-handedness in their families--who may share brain characteristics with their left-handed relatives--outscored those without (with so few lefties in the population, the scientists focused on lefty "families" instead). Regardless of their own handedness, subjects with lefty relatives achieved an average score of 4.7 compared to 2.7 for those with only right-handed relatives. There was no such difference in a second task designed to test factual memory.
Armed with these results, the pair sought to confirm the role of interhemisphere interaction. They asked 46 subjects to view a set of words with either their left or right eye, each of which is wired to one hemisphere. After a pause, they tested episodic memory by asking the subjects to distinguish these words from new words. Subjects did better when they saw the choices with the opposite eye, rather than the same eye that had seen the first words. In a test of factual memory, however, subjects did better when the second presentation was made to the same eye as the first. The researchers say that this supports the idea that interhemispheric processing is uniquely important for episodic memory, helping to explain the lefties' episodic memory advantage.
The study is "very interesting," says Sandra Whitelson of McMaster University in Ontario, because it takes a complex cognitive ability--episodic memory--and shows that it is linked to a brain structure.