Kiwi scientists have published another study exploring links between concussions suffered while playing rugby and long-term impacts on brain function.

The new study, just published in the New Zealand Medical Journal, failed to find a firm connection between concussion and certain brain issues in later life - but its lead author says more research is needed.

The issue has increasingly come under the spotlight over recent years, with New Zealand Rugby and Statistics NZ last year launching an inquiry into possible increased risks of dementia.

It followed an unscientific Herald series about possible links between rugby and dementia experienced by a number of All Black and Taranaki rugby legends.

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In August, New Zealand research revealed a definitive link between concussion in rugby players and cognitive difficulties following retirement.

Players who experienced one or more concussions during their career were found to perform worse in tests that measure cognitive flexibility, complex attention, executive function and processing speed.

But findings of the new study, published last week, were less clear.

The new paper compared corticomotor function - the function of neural pathways from the brain that control movement - between former rugby and non-contact sport players.

While elite rugby players were found to have different corticomotor function, the study found no evidence that this was related to previous concussions.

Part of the wider Rugby Health Study conducted by Auckland University of Technology (AUT), in partnership with New Zealand Rugby and World Rugby, the study investigated brain excitability and inhibition in retired rugby players at elite and community level.

The results were compared to a control group of former non-contact sport players.

The researchers found evidence of altered corticomotor function in the retired elite rugby players compared to the non-contact sport control group.

Resting motor threshold was elevated - reflecting reduced excitability, and long-interval intracortical inhibition (LICI) was increased - indicating enhanced inhibition, echoing some of the existing research on the impact of concussion on measures of motor cortex excitability.

Yet the study found these changes were not evident in those who had played club level rugby.

Both groups of retired rugby players had experienced more concussions than the non-contact sport group; 87 per cent of elite level and 85 per cent of community level players had experienced three or more concussions, compared with four per cent of non-contact sport players.

Because of the absence of altered corticomotor function among the community rugby players, the association between elite players' altered corticomotor function and previous concussions was found to be unclear.

AUT Associate Professor Gwyn Lewis, who led the study, said the larger build of the retired elite players could be a factor in the corticomotor performance differences identified.

"The elite rugby participants were significantly taller and heavier than the non-contact sport players, and had a higher body mass index - characteristics that may have contributed to their increased resting motor threshold."

But she emphasised there was a need for further research.

"The study has established the need for further research into this aspect of rugby players' long-term health.

"Current and future elite players would benefit from learning more about the differences in motor cortex function they may experience, which can impact the ability to learn and perform new motor skills."