This week, with the Rugby World Cup in full swing, the sports chief medical officer, Martin Raftery has called for changes to be made to the rules in order to cut the number of concussions suffered by players. Concussion occurs when the brain is shaken around inside the skull. This damages nerve cells and blood vessels, and the effects of the damage are worse if a person is already suffering from a prior concussion. Finding ways to spot who is concussed, and when it's safe for them to play on, is a priority. Ginny Smith spoke to two scientists studying concussion. First, Michael Grey, from the University of Birmingham, followed by Dr Matthew Campbell from Trinity college Dublin.