Researchers say the jerking motions and gravitational forces on two roller coaster rides caused a four-year-old boy to have a stroke.

The unnamed child was the subject of a Pediatric Neurology case report published three weeks ago.

The boy travelled to an amusement park in May 2013 with his family, and rode on a coaster 679 feet long and 30 feet high, with speeds of up to 25 miles per hour. The second coaster reached 53 feet at its highest point, and speeds of up to 40 miles per hour.

In what Loyola University Chicago Stritch School of Medicine Neurology Department Chairman Dr Jose Biller called a rare occurrence, the child suffered a torn carotid artery from the rides. The tear resulted in a blood clot which travelled to his brain, causing a stroke.

The following day, the preschooler began vomiting, and experienced weakness on the left side of his face during his flight home. He was also unable to walk.

Medical testing diagnosed the stroke, and the boy was given low-dose aspirin. Dr Biller, who treated the child, said he is slowly improving.

"He walks with a limp and he needs help getting dressed," he told CBS News via email. "But he can move his left arm and grip things. He has no speech problems, and he is doing above average in school. He is taking karate classes as part of his therapy."

The injury that the child suffered can also be the result of whiplash.

There are several cases of adults suffering strokes after riding roller coasters, but only two other cases involving children. One boy, an 11-year-old, experienced a week-long headache after the roller coaster he was on came to an abrupt stop. When the headache subsided, he rode more coasters.

Doctors diagnosed him with a torn carotid artery after he reported weakness, paralysis, loss of coordination, dizziness, nausea, and vomiting. He reportedly made an excellent recovery.