What is the factor that makes social networks tick and catalyses mass mobilisations in revolutions and protest movements worldwide?
An Oxford University study of Twitter finds that the most influential group comprise a small number of users close to the centre of a network, described as 'spreaders.'
The 'spreaders' play a critical role in triggering chains of messages reaching huge numbers of people.
However, early participants and those starting the recruitment process have no hierarchy within the network. They are the leaders of the movement and first movers in their local networks.
They spark the initial online activity that recruits the spreaders, but they are scattered all over the network, suggests the study.
Sandra Gonzalez-Bailon from Oxford University's Internet Institute (OII), with colleagues from the University of Zaragoza, Spain, led by Yamir Moreno, analysed Twitter activity data during mass protests in Spain in May 2011.
These protests were sparked by the political response to the financial crisis, resulting in demands for new forms of democratic representation.
The main target of the campaign was an organised protest on May 15, which brought tens of thousands of people to the streets of 59 cities all over the country.
Researchers followed the posting behaviour of 87,569 users and tracked a total of 581,750 protest messages over a 30-day period.
They found that the growth of the movement was driven by two parallel processes: the recruitment of users, started by early participants who provided what the study calls 'random seeding'; and the diffusion of information, which made the movement grow from those roots by means of the 'spreaders'.
Gonzalez-Bailon said, "Digital media has played an important role both in the recent wave of mobilisations in the Arab world and in protests across Western countries, such as the Occupy Movement across cities worldwide."