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What happens inside the skull of a soccer player who repeatedly heads a soccer ball? That question motivated a provocative new study of the brains of experienced players that has prompted discussion and debate in the soccer community, and some anxiety among those of us with soccer-playing offspring.

For the study, researchers at the Albert Einstein College of Medicine in New York recruited 34 adults, men and women. All of the volunteers had played soccer since childhood and now competed year-round in adult soccer leagues. Each filled out a detailed questionnaire developed especially for this study to determine how many times they had headed a soccer ball in the previous year, as well as whether they had experienced any known concussions in the past.

Then the players completed computerized tests of their memory and other cognitive skills and had their brains scanned, using a sophisticated new M.R.I. technique known as diffusion tensor imaging, which can find structural changes in the brain that would not be visible during most scans.

The researchers found, according to data they presented at a Radiological Society of North America meeting last month, that the players who had headed the ball more than about 1,100 times in the previous 12 months showed significant loss of white matter in parts of their brains involved with memory, attention and the processing of visual information, compared with players who had headed the ball fewer times. (White matter is the brain’s communication wiring, the axons and other structures that relay messages between neurons.)

This pattern of white matter loss is “similar to those seen in traumatic brain injury,” like after a serious concussion, the researchers reported, even though only one of these players reported having ever experienced a concussion.

The players who had headed the ball about 1,100 times or more in the past year were also substantially worse at recalling lists of words read to them, forgetting or fumbling the words far more often than players who had headed the ball less often.

“Based on these results, it does look like there is a potential for significant effects on the brain from frequent heading,” says Dr. Michael L. Lipton, associate director of the Gruss Magnetic Resonance Research Center at Einstein and senior author of the study.

For decades, there have been intimations that heading could have undesirable consequences, including reports in the late 1980s and early ’90s of memory deficits in retired, professional Scandinavian soccer players. But those studies depended on players’ slippery recall of the number of times they had headed during their entire careers and didn’t take into account alcohol use or a history of severe concussions, and the findings generally have been dismissed as unreliable.

Then last year, Elizabeth Larson, a researcher at Humboldt State University in California, carefully tracked the heading history and cognitive health of 51 male and female soccer players at the school, a Division II program, over the course of a full collegiate season. She found that the players who headed the ball most often during the season, whether in practices or games, performed significantly worse on tests of visual memory, including the ability to recall shapes and images, than they had at the start of the season. Those players also reported more headaches and episodes of dizziness than other players.

“Physiologically, it makes sense” that verbal and visual recall might be affected by frequent heading, said Ms. Larson, who now coordinates the North Coast Concussion Program at the university. Those memories are partially processed in the front and rear of the brain, “the areas that bump against the skull when you head the ball,” she says.

In confirmation, the new imaging study showed that the frontal lobe, just behind the forehead, and the temporo-occipital region, at the bottom-rear of the brain, were the areas displaying the most damage among the high-frequency headers.

So what’s a soccer parent to do?

“What our research shows is that there appears to be a threshold” – about 1,100 or so balls headed in a single year, a substantial number — “beyond which heading may be problematic,” Dr. Lipton says. “Below that threshold, it appears that heading is safe. So our research is actually optimistic, I think.”

Many questions, however, remain — especially about the impact of heading in young players, which has not to date been studied. “On the one hand, kids’ brains are developing fast, so they might experience more problems” than adults, Dr. Lipton says. “On the other hand, their brains are renowned for their plasticity, so maybe they’ll recover better. We just don’t know.”

The practical significance of any brain damage is also uncertain. None of the players who scored poorly on cognitive tests in the Einstein or Humboldt State studies had noticed any memory problems. “The effects, such as they are, seem to be subtle,” Ms. Larson says.

Still, she recommends some preemptive steps, based on the current science. “There is a growing consensus that kids younger than 12 shouldn’t be heading,” she says, and parents should monitor the number of heading repetitions and any accompanying symptoms in older children. Ask your child if he or she experiences headaches or dizziness after practice and, if so, “check with the coach about reducing the frequency of heading drills.

“No one is suggesting that heading should be outlawed,” she concludes. But science and common sense both indicate that “it’s almost certainly not a good idea to practice heading over and over and over.”