A comprehensive neuropsychological study of retired professional hockey players shows that head trauma is associated with an elevated rate of psychiatric disorders.

Published in the Journal of Neurology, Neurosurgery, and Psychiatry, the study looked at 33 retired NHL players, ranging in age from 34 to 71, four-year period.

It found 59 per cent experienced disorders, including depression, anxiety and substance abuse. With concussions going hand-in-hand with high-impact sports, some players are calling on the National Hockey League to revise its approach to head injuries.

"The professional athletes were compared to group of control subjects in the same age group with no history of participation in high-level contact sports and no history of significant concussions," said Brian Levine, senior scientist at the Rotman Research Institute at the Baycrest Health Sciences centre in Toronto.

Although the athletes were free of significant impairment on tests of mental and cognitive function, Levine says there were subjective reports that indicated the athletes had "high level behavioural, cognitive and emotional problems in comparison to the control group."

Those who had experienced a large number of concussions had lower scores on tests of problem solving and intellectual function than those of the comparison group.

'Short-term memory is a struggle,' ex-NHLer says

Scott Thornton, formerly of the Toronto Maple Leafs, was one of the participants.

Throughout his 17 seasons playing in the NHL, Thornton, 46, says he suffered numerous concussions and is now concerned about his memory.

"If I'm not sleeping and get fatigued, that's when short-term memory is a struggle," said Thornton.

All participants had to complete tests, computerized tasks and brain imaging studies.

Levine says he plans to follow the players as they age to get a full understanding of how their mental function might change.

'Head trauma is different'

After experiencing concussions himself, Thornton says the way players and the NHL handle them has to improve.

"The decisions can't be in the players' hands. We come from a generation where we're supposed to be tough. There's a pride in playing injured — that's how you gain respect," said Thornton.

"Head trauma is different. It isn't something you can shake off. Management and trainers have to step up and say, 'No, this isn't right; this kid can't play.'"

The NHL is currently being sued by more than 100 former players.

They claim the league puts profits over the long term health of the players, and that they were often pushed back on the ice before they completely recovered from head injuries.