Lefties, righties take neural sides in perceiving parts

Scientists have uncovered a new brain difference between right-handers and left-handers. For righties, a region near the back of the left brain fosters the capacity to focus on distinguishable parts of an object rather than on the whole entity, as previous research indicated. For lefties, a corresponding right brain area promotes the same capacity to see the proverbial trees while ignoring the forest, according to a team led by Carmel Mevorach of the University of Birmingham in England.

TAKING PART. In a new study of handedness and brain function, volunteers tried to identify parts of objects, such as letter Ds within a larger H (top) or squares within a cross (bottom), as quickly as possible. Nature Neuroscience

The scientists probed 11 right-handed and 11 left-handed adults using transcranial magnetic stimulation (TMS). Each volunteer sat under a coil that delivered low-intensity magnetic pulses through the skull to either of the corresponding brain areas, temporarily disrupting neural activity there. Participants used a computer to view a series of letters and shapes composed of smaller parts, such as a large letter H composed of 10 small letter Ds. Before and after a bout of magnetic stimulation, the volunteers were asked to identify as fast they could on the computer display either parts of an object or the whole object.

The time required to identify parts of objects increased markedly when the scientists briefly disabled either the key left-brain region in right-handers or the equivalent right-brain region in left-handers.

The findings appear in the March Nature Neuroscience.

Bruce Bower has written about the behavioral sciences for Science News since 1984. He writes about psychology, anthropology, archaeology and mental health issues.