Icer Jurgen Cautreels was skating behind the net when he was levelled by a Mercyhurst check on Jan. 6, his head slamming against the Plexiglas surrounding the rink. The freshman forward made his way back to the bench. He lost his vision during the trip -- a trip he doesn't recall finishing.

"I remember skating to the bench, and the next thing I know I'm waking up on the bench," Cautreels said. "Supposedly, someone pulled me off (the ice)."

Cautreels was diagnosed with a concussion as a result of the head-first smash into the boards, adding his name to a growing list of athletes who have been nailed by one of sports' most common, yet least understood, injuries.

Concussions were brought into public consciousness by the National Football League's autumn wars of attrition. This past season, when players in the league's glamour-boy position -- quarterback -- were stung with several concussions, people started to take notice.

NFL quarterbacks Troy Aikman, Chris Miller, Vinny Testaverde, Dave Brown, Chris Chandler, Jeff Hostetler and David Klingler all suffered head injuries in games during the 1994-95 campaign.

But the highest profile case belongs to running back Merril Hoge. The former Chicago Bear and Pittsburgh Steeler ended his career last October after suffering two concussions in a six-week span.

Like Hoge, a Penn State athlete had his career halted prematurely in 1994 by a concussion. Another one is gone for the season and hoping for a medical redshirt.

Redshirt junior Josh Kroell suffered a concussion in August that ended his stint as a free safety for the football team.

And senior Katina Mack, a guard on the women's basketball team, suffered a severe concussion in a November game. She returned to action a month later only to suffer another one.

Mack said she hopes the NCAA will grant her a redshirt so she can play for the Lady Lions again.

Just as questions surround Mack's future at Penn State, they also surround the true nature of concussions.

"Most people think of them as some sort of transient deficit in mental function," said Dr. Margot Putukian, a Penn State team physician.

Putukian said for the most part, those mental deficits are caused when the brain shakes violently. The shaking can occur when rapid acceleration or deceleration, or a shot to the head, causes the brain to strike one end of the skull and then come back and strike the other end, she added.

There are three classifications of concussions, each determined by the severity of the injury. Putukian said although classifying concussions is important, "there are as many ways to grade concussions as there are people to grade them."

Putukian rates concussions in the following manner:

-- A grade 1 concussion is the least severe and is characterized by slight confusion with no amnesia or loss of consciousness.

-- A grade 2 concussion involves confusion and amnesia. The victim does not recall the events leading up to or immediately following the impact, but does not lose consciousness.

-- A grade 3 concussion results in the loss of consciousness and is the worst concussion that can be suffered. Mack's season-ending injury was a grade 3 concussion, and the worst case that Putukian said she has ever encountered.

Mack hit her head so badly that she lost strength in her upper body for almost two hours, Putukian added.

However, the effects of a concussion can extend far beyond just two hours.

Just ask Kroell. He suffered fatigue and forgetfulness for two weeks after his concussion, and fought headaches for two months.

"I'd be walking to class and if somebody was walking really slow in front of me I'd get real mad," Kroell said. ''I was just real irritable. My head was killing me all the time."

What Kroell was experiencing was post-concussion syndrome, which can also include tunnel and blurred vision, dizziness and nausea. It affects many concussion sufferers, like Rams' quarterback Miller.

Miller bruised the frontal lobe of his brain when it collided with the inside of his skull when his head hit the turf. Miller told Sports Illustrated that a concussion-induced fog lasted for weeks and "was like the morning after you've drunk a bottle of tequila."

For Kroell, there was little he could do to alleviate the pain.

"If I would just lay down and not really do anything," he said. "That's the only time the pain would go away."

Kroell's concussion was one of many in college football last season -- it is football's fifth most-common injury. Randy Dick, NCAA's assistant director of sports sciences, said the governing body has monitored injuries in football since 1984. He said the NCAA has noticed an increase in concussions.

"The concussion injury rate has grown slightly over the years," Dick said.

"The helmet wasn't originally designed to protect against concussions," he said.

This led to the invention of the Pro Cap -- a half-inch rubber attachment placed on top of the helmet and secured by Velcro straps. The Pro Cap, developed by Protective Sportswear, Inc. in Erie, is just one way the NFL is cutting down on concussions.

"(The NFL) always examines and comes up with ways to prevent injuries," an NFL spokesman said.

Another way to cap the concussion carnage is to properly treat the head shots and allow as much recovery time as possible.

"(Doctors) send the kids back in there pretty lightly a lot of times," Putukian said, "and some people are left with some deficits."

Something even more severe than a mental deficit can occur with the second-impact syndrome -- a condition that is conducive to major problems if a player suffered a concussion and is thrust back into action, and suffers another injury.

"If you have an initial head injury, and you're not completely recovered and you sustain a second injury, then it can lead to increased (swelling) in the brain," Putukian said. "That could ultimately lead to death."

The knowledge of this syndrome is problematic for athletes when the time comes for them to play again.

''There's always fear," said Penn State psychologist Dave Yukelson. "They ask themselves, 'What if I get hit again?' "

Mack asked herself that question. And unfortunately for her, it was answered. It took her one month to get over the persistent headaches she suffered as a result of her first concussion.

Once she did, she was greeted back into the Lady Lion lineup by an elbow to the head from Ohio State forward Katie Smith.

"I was like, 'Damn, I can't believe this happened again,' " Mack said. "I was stunned."