Paul Marsden: 'The urge for copycat attacks is hardwired into us'

Am I surprised? No I am not.

There is evidence that terrorism is a copycat phenomenon. In the weeks following a terrorist attack there is a greater likelihood that there will be further terrorist incidents in that area. Just after 11 September a young boy crashed a small plane into a building in Florida.

Copycat events tend to peak around 10 days to two weeks after the first incident. We don't know why, that's just what the statistics show us.

The people who commit copycat attacks tend to share characteristics with the first attackers. They are likely to feel that they are in a similar position to the earlier attackers either psychologically or socially or by being part of a similar group. I would not want anyone to assume that this means it must be people from Leeds or who are Muslims. But the psychological theory of differential identification says that copycats see these people as role models.

The way the media report these events is crucial as it is important not to personify the people who commit these attacks. If the person who commits a terrorist attack is seen as a real person then people who share similar characteristics to the attackers - such as gender, age, or circumstances - can be triggered into copycat attacks.

One of the key theories about social learning explains that we learn from other people rather than on our own. Part of that phenomenon is role modelling but there is also a phenomenon of "disinhibition" which occurs when suicidal or murderous thoughts - inhibited by conscience, uncertainty or fear - are exposed to what is perceived as the positive consequences of suicide or murder. When this happens, the mental conflict between urges and inhibitions may be resolved, resulting in a suicidal and possibly murderous mind being made up. Thought is free to become deadly action.

These are likely to be people who want to commit an act but would not normally do so for fear of the negative consequences. They would be people in intra-psychic conflict - or put simply "shall I or shan't I". They will have weighed up the risks and rewards of acting and decided not to act until they were triggered to do so by observing the first attacks.

The urge to copycat seems to be hardwired into us. Emotions are contagious - we copy smiling, yawning and even vomiting from those around us. It also works at a behaviour level - murder, suicide and eating disorders seem to spread by the power of suggestion.

The same is true of terrorism. We need to think carefully about how the Government and media respond to these attacks. As a consequence of our own reactions - by sensationalising the event, simplifying it or personalising those responsible - we may increase the likelihood of copycat terrorism.

The way the Government and the media responds can act as a trigger for copycat attacks. It is the same as suicide.

If somebody is in the news for having committed suicide in a particular way, there will be a spate of similar suicides just afterwards using the same method.

The first act psychologically primes people's minds towards acts of aggression. The nature of terrorism is that the target of the London attacks a fortnight ago were not the people on the subway. It was the people who saw it on television. The terrorists hoped to create a contagion of terror within the community. It is an act which requires spectators.

It is of course perfectly possible that yesterday's attacks were planned all along. We obviously cannot know for sure but my feeling is that they are copycat attacks.

Dr Paul Marsden, psychologist at London School of Economics, is an expert on copycat phenomena