A brain-damage advantage for lefties?

A brain-damage advantage for lefties?

For an as yet unexplained reason, people who are predominantly left-handed apparently are able to withstand moderate brain damage with relatively few of the motor problems observed in righthanded victims of brain damage.

Studies of a limited number of braindamaged left-handers also indicate that they have a quicker and superior recovery of other functions, such as language and visual-spatial processing, than do their right-handed counterparts, says neuropsychologist Jordan Grafman of Walter Reed Army Medical Center in Washington, D.C.

"You can speculate that more transfer of information and shared information processing between left-handers' brain hemispheres might allow for their better recovery after brain damage,' observes Grafman. "But so far there is no evidence for this theory.'

Grafman and his colleagues chose subjects from a group of left-handed Vietnam veterans who suffered brain wounds without paralysis about 15 years ago. The study sample was composed of 13 men with right-hemisphere damage, 11 with left-hemisphere damage and 13 healthy, non-brain-damaged veterans. The researchers administered eight tests of simple motor functions, including grip strength, finger dexterity (manipulating pegs on a pegboard), coordination (finger tapping and movement tasks) and reaction tim (pressing a button as rapidly as possible after seeing a brief flash of light).

Left-handed veterans with damage to either hemisphere performed almost as well as the healthy controls and displayed no severe motor problems, report the investigators in the October PERCEPTUAL AND MOTOR SKILLS. The size of a brain would, language comprehension and preinjury intelligence scores were not related to motor performance, they note. Curiously, says Grafman, patients with left-hemisphere damage were more likely to have received both physical and occupational therapy, although the reasons for this are unclear.

In an unpublished study conducted by the same scientists, substantial deficits in motor functioning on the same tests appeared among right-handed veterans who suffered damage to either brain hemisphere, compared with a control group.

There are some data suggesting that left-handers have a more equitable distribution of motor and cognitive skills across brain hemispheres than right-handers (SN: 8/17/85, p. 102), as well as indications that left-handers are more likely to have allergies, myopia and learning disabilities, and, paradoxically, are more likely to be intellectually gifted (SN: 4/27/85, p. 263). "It's not clear if left-handers have a developmental disadvantage [compared with right-handers] and an advantage in adapting to brain damage,' says Grafman. One reason he is reluctant to interpret his data is that it was not possible to conduct handedness tests on braindamaged veterans before their injuries occurred. Also, it is not known if healthy left-handers have somewhat poorer motor skills than healthy right-handers across a critical range of performance affected by brain damage; if this were the case, explains Grafman, deficits would appear more pronounced in right-handers because they have more motor ability to lose.

"Unfortunately,' he notes, "there is a lack of studies on left-handers, and it's hard to develop an animal model of handedness.'