A biomedical journal has sparked debate about transparency and the limits of peer review after announcing that it will no longer accept extra material submitted with academic papers.

Until now, in common with many scientific journals, The Journal of Neuroscience has hosted supplementary material - additional content that can accompany published articles - on its website.

But John Maunsell, the journal's editor-in-chief, says the volume of this content has grown exponentially since it was first accepted in 2003 and is rapidly approaching the size of extra articles.

In an editorial, he argues that the limits on reviewers' time means it is impossible to review such material as rigorously as main articles.

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Supplemental material has "begun to undermine the peer-review process in important ways", he writes. "It is obvious to editors that most reviewers put far less effort (often no effort) into examining (it). Nevertheless, we certify the supplemental material as having passed peer review."

Such material also provides "a place for critical material to get lost" and encourages "excessive demands" from reviewers, with researchers asked to do extra experiments specifically for it.

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"These additions are invariably subordinate or tangential, but they represent real work for authors and delay publication," he writes.

In future, authors will be able to embed videos in main papers on the journal's site plus links to supplemental material on their own websites, "with the clear warning that the material has not gone through peer review".

Peter Lawrence, emeritus researcher in the department of zoology at the University of Cambridge and former editor of the journal Development, described the move as "brave, serious and sensible".

He agreed that reviewers "mostly don't bother" with supplemental material, while most readers did not have time to look it up. Authors "often use it as a vanity cupboard to put in material they are fond of".

"Science will be served by a reimposition of rigour and discipline," Dr Lawrence added.

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But Julian Davis, professor of medicine at the University of Manchester and former editor-in-chief of the Journal of Endocrinology, said journal websites were good places to host increasingly large datasets relating to specific papers.

Journals were not taking a "huge risk" by hosting supplemental material, he added, while peer review was no guarantee of veracity.

A spokesman for open-access publisher BioMed Central said it regarded supplemental material as "integral" to its articles.

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Publishing such material, especially raw data supporting article findings, "serves to increase transparency and reproducibility: a core principle of the scientific method".

He claimed that journal sites were the best place to ensure that the extra information remained permanently available.

Jim Milne, editorial director of the Royal Society of Chemistry, which publishes a number of journals, said such material had not grown as quickly in chemistry as in the life sciences. He currently had no concerns about its volume.

Brian Foster, head of the department of particle physics at the University of Oxford, said physics papers were still entirely self-contained.

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paul.jump@tsleducation.com.