http://www.iflscience.com/health-and-me ... ough-pluck
We demonstrated that plucking a few properly arranged hairs can trigger regeneration of hair follicles stem cells in up to five times more neighbouring, un-plucked surrounding hairs.
It is not surprising that follicle stem cell injury – caused by plucking – can cause a regeneration response. But, generally the stimulation of one stem cell through injury is only thought to cause regeneration in that stem cell alone. Triggering the regeneration of a whole head of hair in this way would be highly inefficient. But can the regeneration response of several stem cells be triggered by stimulating only a few key cells or signals?
Decision Making In Stem Cell Populations
Recently, we accidentally discovered that regeneration could occur through a collective decision-making process. By plucking the correct number of hairs with a proper arrangement, up to five times more neighbouring, unplucked resting hairs were activated to regrow. But if the number of plucked hairs was below a threshold, no hairs regenerated.
This type of regeneration is an all-or-nothing process which is dependent on the signals produced by a fraction of hairs being plucked, and is an example of the process known as “quorum sensing”.
Quorum sensing can be thought of as a decision-making process which is dependant on certain criteria being met within a population. Signalling molecules are released by each stimulated component of the population, the more components that are stimulated the more signal molecules are released. As the elements in the system are able sense the number of signal molecules released by the population as a whole, they can also sense the degree of stimulation. When a certain threshold of stimulation is reached, a collective response from the components in the system will follow.