WASHINGTON, D.C.--A key congressional oversight committee announced today that it was opening an investigation into the basis of a decision by the Pentagon's health plan to deny a type of medical treatment to troops with brain injuries.

Sen. Claire McCaskill, D-Mo., the chairman of the subcommittee on contracting oversight, said she wanted to examine a contract issued by Tricare, an insurance-style program used by soldiers and many veterans, to a private company to study cognitive rehabilitation therapy for traumatic brain injury. Such injuries are considered among the signature wounds of the wars in Afghanistan and Iraq.

The study, by Pennsylvania-based ECRI Institute, found insufficient or weak evidence to support the therapy. Often lengthy and expensive, cognitive rehabilitation programs are designed to rewire soldiers' brains to conduct basic life tasks, such as reading books, remembering information and following instructions. ECRI's findings ran counter to several other studies, including ones sponsored by the Pentagon and the National Institutes of Health, which concluded that cognitive rehabilitation was beneficial.

In a letter to Defense Secretary Robert Gates, McCaskill cited an investigation by ProPublica and NPR in December, which found that top scientific experts had questioned the Tricare-funded study in confidential reviews, calling it "deeply flawed" and "unacceptable."

"If true, these reports raise significant questions regarding the Department's award and management of the contract with ECRI Institute, and may have profound implications for hundreds of thousands of injured service members and their families," McCaskill wrote. "We owe it to our brave service members to find the truth."

The ProPublica and NPR investigation also found that senior Pentagon officials have worried about the high price of the care, which can cost more than $50,000 per patient. Some studies estimate that as many as 400,000 troops have suffered traumatic brain injuries in the war zones, though only a small percentage of them would need a full-scale program of cognitive rehabilitation therapy.

McCaskill joins a growing chorus demanding that Tricare reconsider its decision to deny coverage for cognitive rehabilitation. In recent weeks, the American Legion, the nation's largest veterans' organization, called on Tricare to provide treatment. Sen. Bob Casey, D-Penn., chairman of the Senate Foreign Relations subcommittee with oversight of the Middle East, sent a letter to Gates asking for an explanation of Tricare's stance.

McCaskill was also one of the senators who signed a letter in 2008 asking Gates to direct Tricare to begin providing cognitive rehabilitation to troops. This November, the Pentagon sent a response to Congress informing them of the Tricare study's findings. George Peach Taylor Jr., then-acting assistant secretary of defense for health affairs, said the Pentagon would continue to study the treatment, with another report expected later this year.

In strongly worded response on Jan. 19, McCaskill said that the senators who signed the original letter believed that enough evidence existed on the treatment's benefits to justify covering the cost for brain-damaged soldiers.

She asked for Gates to provide her committee with a series of documents on the contract and critical scientific reviews by Feb. 18.

"While we agreed that further research on cognitive rehabilitation therapy was appropriate, we also called on the Defense Department to err on the side of providing this proven treatment to service members," McCaskill wrote.

ProPublica and NPR have filed a similar request under the Freedom of Information Act, but Tricare has denied access to the documents, giving contradictory explanations for why. ProPublica and NPR have appealed.

Tricare officials have said their decision to deny cognitive rehabilitation is based on regulations requiring scientific proof of the efficacy and quality of treatment. They have said that the study by ECRI highlighted a lack of rigorous evidence proving the therapy's benefits.

Tricare officials also noted that the agency does cover some types of treatment considered part of cognitive rehabilitative therapy. For instance, Tricare will pay for speech and occupational therapy, which plays a role in cognitive rehabilitation. Tricare officials deny that cost played any role in their decision. In a statement, Tricare said the care of troops was their "utmost" concern.

Tricare did not immediately return requests for comment on McCaskill's investigation.

ECRI defended its study. The non-profit institute, which has carried out numerous health reviews for Tricare, other agencies and hospital and medical groups, said they applied standard protocols in reviewing scientific literature about the efficacy of cognitive rehabilitation therapy. ECRI provided a document explaining its review here.

"The issue of how well cognitive rehabilitation therapy works for traumatic brain injury is important," said Jeffrey C. Lerner, the president and CEO of ECRI Institute. "ECRI Institute is fully committed to providing information to the U.S. Senate on our report and methodology."