Scientists are a step closer to cracking the mystery of cot death. New research suggests that an inability to gasp - a reflex that automatically restarts breathing - might put some babies at risk.

Nobody is certain what causes cot death, also known as sudden infant death syndrome (Sids). It is the leading cause of death in babies over one month old, taking more lives than meningitis, leukaemia or any form of cancer.

A failure to gasp - also called autoresuscitation - has been proposed as a possible biological mechanism behind Sids. In new experiments, Julian Paton at Bristol University found that the brain has a set of pacemaker cells that control the gasping reflex. Problems with these cells might prevent babies from restarting breathing when it stops. The work is published today in Nature Neuroscience.

Prof Paton worked with US respiration experts to find out how gasping works. His work found that, while many types of brain cells are required for breathing, only a small subset is required to gasp. By gasping, oxygen supplies are restored and the heartbeat is jolted back into action so that normal breathing can begin again.

"We have discovered a mechanism within the brain that allows autoresuscitation of both breathing and the heartbeat to come about when oxygen levels are critically low," said Jeffrey Smith, of the National Institutes of Health in the US.

The brain cells responsible for this gasping mechanism depend on a protein that creates a tiny pore in the walls of the cells. When oxygen levels are low, the pore opens up and allows the passage of electrically charged sodium atoms into the cell. If this pore is blocked or not present, the ability to gasp is blocked. The researchers speculate that a genetic defect might lie behind problems with the protein responsible for creating the pores.

Walter St John, of Dartmouth University in the US and an author on the paper, said: "This result explains why gasping is such a powerful mechanism for autoresuscitation."