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In the last few years some people have raised the issue of whether subconcussions in chidren, teenagers, and adults playing football also leads to brain changes similar to concussions. Subconcussions are head impacts that aren't as strong as concussions, but they routinely happen to players in football games and practice. Research says YES - worrying brain changes are occurring from subconcussions, but long-term effects from them are currently unknown. Earlier research found that the brains of high school football players (who had only received head impacts during the season) don't fully heal during the off-season when football is not played. (More related posts on subconcussions: high school players, football before age 12, teen football players, soccer players). The research discussed below is ongoing research. From Medical Xpress:

Subconcussions cause changes to brain, study of college football players shows

The average college football player receives about 1,000 head impacts each season. Some of these hits result in concussions – traumatic head injury that results in short-term, and possibly even long-term, damage to brain function. But what are the effects of the hundreds of routine head impacts, called subconcussions, that occur during a four-month season of practice sessions and games?

A University of Virginia neuroscience Ph.D. candidate is trying to find out. Using functional magnetic resonance imaging – fMRI – Bryson Reynolds studied the brain activity and connectivity of a group of healthy college football players, before and after a competitive season, and compared the data to brain-activity scans of healthy male college soccer and lacrosse players, and to a control group of college male non-athletes.

He found that the football players experienced a disruption in "local functional connectivity" – the way different areas of the brain communicate with each other – while soccer and lacrosse players' brain activity did not noticeably change after a competitive season. The result for the soccer and lacrosse players was comparable to the control group, which also displayed no brain activity changes during a four-month period. "This is an important discovery regarding the football players because a similar disruption of local functional connectivity has also been found in athletes diagnosed with a concussion," Reynolds said.

"We have no ideas how these subconcussions might be affecting players' brains, but we are seeing concussion-like changes to the brain, at least in the short term," Reynolds said. "This does not necessarily mean that something bad is happening to the brain, but clearly some changes are occurring over the course of a season."

Neurologists know that concussions cause headaches, dizziness and sometimes loss of consciousness, and may also increase the risk for developing serious long-term neurodegenerative disorders, such as Alzheimer's disease, amyotrophic lateral sclerosis and chronic traumatic encephalopathy.

In other words, repeated head impacts over the course of a season, or perhaps a career, may be affecting the brain in ways not yet understood, but possibly similar to actual concussions. Reynolds' study did not include players who suffered concussions, and the subconcussions he observed were not causing perceptible problems or symptoms for the players. But the disruptions in brain activity recorded in the fMRI scans may indicate subtle changes that could be part of a larger picture. 

New research showed that eight days after a concussion, the concussed athletes (football players) looked and felt like they had recovered (clinical recovery), but MRIs showed that there were still neurophysiological abnormalities (significant blood flow decrease) in their brains. They did not look at if and when the blood flow returned to normal, but that research also needs to be done.

It is very disturbing to look at both this research and also the finding that the off-season is not enough for high school football players to recover from the repeated hits (not concussions, but sub-concussive hits) that they receive during the football season (Nov. 24, 2015 post). Do student football players really know and understand the dangers to their brains from the repeated hits and also concussions that occur in football? From Medical Xpress:

Reduced blood flow seen in brain after clinical recovery of acute concussion

Some athletes who experience sports-related concussions have reduced blood flow in parts of their brains even after clinical recovery, according to a study presented today at the annual meeting of the Radiological Society of North America (RSNA). The results suggest a role for MRI in determining when to allow concussed athletes to return to competition.

Decisions to clear concussed athletes to return to action are typically based on symptoms and cognitive and neurological test results. However, there is increasing evidence that brain abnormalities persist beyond the point of clinical recovery after injury. To find out more, researchers from the Medical College of Wisconsin in Milwaukee studied concussed football players with arterial spin labeling, an advanced MRI method that detects blood flow in the brain.

Dr. Wang and colleagues studied 18 concussed players and 19 non-concussed players. They obtained MRI of the concussed players within 24 hours of the injury and a follow-up MRI eight days after the injury and compared results with those of the non-concussed players. Clinical assessments were obtained for both groups at each time point, as well as at the baseline before the football season.

The concussed players demonstrated significant impairment on clinical assessment at 24 hours post-injury, but returned to baseline levels at eight days. In contrast to clinical manifestation, the concussed players demonstrated a significant blood flow decrease at eight days relative to 24 hours post-injury, while the non-concussed players had no change in cerebral blood flow between the two time points.

"In eight days, the concussed athletes showed clinical recovery," Dr. Wang said. "However, MRI showed that even those in clinical recovery still had neurophysiological abnormalities. Neurons under such a state of physiologic stress function abnormally and may become more susceptible to second injury." "For years, we've relied on what athletes are telling us," Dr. McCrea said. "We need something more objective, and this technology may provide a greater measurement of recovery."