Even without getting a concussion, taking hits to the head still has the potential to affect a person's learning and memory abilities, depending on the strength of the blows and how frequently they occur.
In new research from the Indiana University School of Medicine, published in the journal Neurology Wednesday, Thomas McAllister and colleagues came to that conclusion after observing college athletes in contact sports (football and ice hockey) and non-contact sports (track, crew and skiing). Of the 80 concussion-free varsity football and ice hockey players, and the 79 non-contact sport athletes from Dartmouth College, those playing contact sports were nearly twice as likely as others to fall into a subgroup of low-performing athletes.
The researchers gave the athletes a test of verbal learning and memory at the beginning of the season, and at the end of the season. In both groups, a subset of athletes performed more than 1.5 standard deviations below expected at the end of the season: 20 percent of the contact players, compared with 11 percent of the non-contact players.
Because there was such a significant difference, McAllister says it warrants further research as to whether there is a subgroup of people who may be more vulnerable to head injuries.
"When you think about it, that's a different kind of public health concern because people are playing these sports and being exposed to hundreds and sometimes more than 1,000 impacts over the course of a season, often playing the sport for many years," McAllister says. "So might it be the case that we need to broaden the discussion from concussion as the marker of concern to frequency and severity of head impacts."
Previously, the team had been studying concussions in athletes, attempting to identify the characteristics of what exactly causes a concussion – the exact severity, the exact speed, and other factors.
Throughout the season, the researchers monitored the contact players through acceleration-time monitors placed on the inside of their helmets, which recorded how hard and how often each player was hit.
But that proved difficult, McAllister says, because it's difficult to pinpoint a concussion to a single blow, as athletes can sometimes hit their heads several times in less than one second.
"It turned out there were some people who were identified with a concussion who got hit really hard, and others who were hit moderately hard, and some who were hit really hard who did not get diagnosed with a concussion," McAllister says. "That got us thinking that concussion is really important but what do we know about impacts to the head that are not associated with the diagnosis of a concussion?"
Using the same in-helmet technology, the researchers turned their focus to athletes without concussions.
What was reassuring in this study, however, was the fact that in the preseason test, there was not a significant difference between the test scores of the contact and non-contact players, McAllister says. If there was a difference, it could suggest that brain damage accumulates and is not recovered during the off-season. But McAllister says the absence of significant test score differences in the beginning of the season, and the presence of some differences postseason, raises the question of whether any previous damage could be recovered during the time athletes are not playing.
Also of note was the fact that among those performing worse on cognition, the amount of change in white matter composition was larger. White matter is a nerve tissue in the brain associated with sending communications and linking memory centers of the brain.
"To me it's a sort of a mixed story," McAllister says. "The good news is that we did not find dramatic preseason differences ... We did however find that there are differences that we think are linked to how hard and how often people are hit in the head. What we don't know is how long those differences last and whether or not there's a permanent kind of effect from that."