After a concussion, adolescents with the highest level of mental activities — such as reading, doing homework and playing video games — take the longest to recover, a new study suggests.

Adolescents engaged in the highest level of mental activities take about 100 days on average to recover from symptoms of concussion, compared to about 20 to 50 days for those with lower mental activities, according to researchers from Children’s Hospital Boston.

A concussion is an injury to the brain resulting from a blow to the head.

Classic symptoms of concussion are confusion and amnesia. Others include headache, dizziness, nausea or vomiting, and fatigue.

The study was published on Monday in Pediatrics, a peer-reviewed, scientific journal of the American Academy of Pediatrics.

One of the authors is a co-developer of the post-concussion assessment software used in the study and is a co-owner of the company that distributes the software.

Researchers tracked 335 people aged eight to 23 who visited a sports concussion clinic in Boston over 21 months. Participants were asked to rate their levels of mental activities on the following scale:

0: Complete cognitive rest (no reading, homework, text messaging, online activity, video games, crossword puzzles or similar activities).

1: Minimal cognitive activity (stay away from the above activities, send less than five text messages per day and do less than 20 minutes per day of online activity and video games combined).

2: Moderate cognitive activity (read less than 10 pages per day, send less than 20 text messages per day and do less than one hour of homework, online activity and video games in total).

3: Significant cognitive activity (fewer activities than normal).

4: Full cognitive activity.

Challenge for students, schools

The results support the benefits of mental rest to recover from a concussion, researchers say. The researchers also back up academic accommodation for student athletes recovering from sports-related concussions, which allows them relative mental rest during the school year.

“For concussion, especially for student athletes, it can dramatically affect their ability to perform in school and it causes a lot more distress than other injuries,” said William Meehan III, director of the Sports Concussion Clinic at Boston Children’s Hospital and co-author of the research.

For the first three to five days after a concussion, Meehan said doctors recommend patients stay away from activities that involve memory or concentration. After that, students should resume some cognitive activity and start with taking fewer courses and delaying high-stake tests that account for a large part of their grade.

“What we usually tell them is do as much school work as you can without making your symptoms worse and without your grades dropping,” he said.

“It’s a hard balance to strike, both for the students as well as the school.”

The study notes, however, that the recovery time is similar for patients in the lowest three groups on the mental activity scale, which suggests that complete abstinence of cognitive activity may be unnecessary.

“Our study would suggest that doing some cognitive activity is not detrimental. It’s really just doing the high level [of cognitive activity] that affects your recovery,” Meehan said.

He added that for most concussion patients, the recovery time is fairly short, ranging from a few days to a few weeks. But for a small group of people, the symptoms can drag on. The next steps for the researchers are to discover treatment to shorten the recovery time for these patients and to find out which patients are more likely to have prolonged symptoms.