Larry Lage, AP

Former NFL player Kyle Turley told members of Congress on Monday that while he still had a severe headache, the St. Louis Rams cleared him for full-contact drills four days after a concussion seven years ago. “Frustrated with being injured and wanting to prove my toughness to my teammates and coaches, I used my head more aggressively than I normally would have in practice, not understanding the damage I was doing to my brain," Turley told the House Judiciary Committee.

“I would like to tell you that this was an isolated incident - just as Dr. Casson would."

Turley, who retired in 2007, was one of several witnesses who took shots at Ira Casson, a neurologist from New York and former co-chairman of the NFL's panel on head injuries.

Under questioning, Casson stuck to his position that there is no proven connection between football head injuries and brain disease.

“There is not enough valid, reliable or objective scientific evidence at present to determine whether or not repeat head impacts in professional football result in long-term brain damage," Casson said.

Rep. Linda Sanchez, D-Calif., and Rep. Steve Cohen, D-Tenn., were skeptical.

“I find it really ridiculous that he's saying that concussions don't cause long-term cognitive problems," Sanchez said. Dr. Randall Benson, a neurologist and professor at Wayne State University, agreed.

“It's easy to wait for absolutes when there are no absolutes in what we do," he said. "I think the questioning was somewhat of a waste of time because we all knew what Dr. Casson was going to say."

Sanchez noted that the league formed its concussion committee in 1994, and wondered aloud whether the NFL's recent moves on concussions took too long to implement. "It seems to me that the NFL has literally been dragging its feet on this issue until the past few years," Sanchez said.

Casson said it was incorrect to characterize the committee as having ignored the problem. He resigned as co-chairman of the NFL's committee on mild traumatic brain injury in November, saying it was a mutual decision between himself and Commissioner Roger Goodell.

"When I heard the first panel, I thought I had come to the wrong room and that I was at a tobacco-industry panel," said Bernie Parrish, who spent most of his career a half-century ago with the Cleveland Browns. "There was a lot of lying."

Casson said more research must be done on the effects of performance-enhancing drugs on the brains of football players. Some lawmakers questioned other witnesses about possible steroid links. Goodell, who was not present, was grilled by lawmakers in October about his league's concussion policies.

Since then, the league has instituted stricter return-to-play guidelines for players showing concussion symptoms and requires each team to enlist an independent neurologist as an adviser. The NFL has also entered into a partnership with Boston University brain researchers who have been critical of the league's stance on concussions, and have recently been conducting tests on helmets. The validity of those tests was questioned by witnesses at the hearing.

Asked for his thoughts on those changes, Casson questioned the merits of the independent neurologist mandate. "We don't know if these independent neurologists have expertise in head injuries," he said. "We don't know if their opinions are going to be independent and reliable and stand up to scrutiny."

Cohen said he sensed the league's recent moves could have resulted from concern about lawsuits. Sanchez also pressed Casson on whether the concept of permanent brain damage and dementia following repeated blows to the head is a very well-established and generally accepted principle in medicine.

Casson refused to give a direct answer, and Sanchez's tone grew more exasperated when she asked whether he would not agree on something most laymen, probably most physicians, would agree with. "We can disagree," he answered.

Another witness, NFL Players Association executive director DeMaurice Smith, told Congress the league hasn't shared the injury data it collected from every player from 2006-2008. "We have written the NFL a letter asking to clarify whether they have given us all the data that they have available or only a portion of it," Smith said after his testimony." As of today, I have not received an answer to that letter."

NFL executive vice president Joe Browne insisted the union has the same injury information that the league collected.