Cooperation and deception through stigmergic interactions in human groups

Stigmergy is a generic coordination mechanism widely used by animal societies, in which traces left by individuals in a medium guide and stimulate their subsequent actions. In humans, new forms of stigmergic processes have emerged through the development of online services that extensively use the digital traces left by their users. Here, we combine interactive experiments with faithful data-based modeling to investigate how groups of individuals exploit a simple rating system and the resulting traces in an information search task in competitive or noncompetitive conditions. We find that stigmergic interactions can help groups to collectively find the cells with the highest values in a table of hidden numbers. We show that individuals can be classified into three behavioral profiles that differ in their degree of cooperation. Moreover, the competitive situation prompts individuals to give deceptive ratings and reinforces the weight of private information versus social information in their decisions.

Early morbidity of endoscopic ultrasound: 13 years' experience at a referral center

BACKGROUND AND STUDY AIM

Endoscopic ultrasonography (EUS) now has an important place in the diagnosis of gastroenteropancreatic diseases. However, prospective data on the morbidity and mortality related to its use are sparse and often retrospective. We attempted to assess the acute and immediate complications of both diagnostic and interventional EUS.

PATIENTS AND METHODS

At our university-affiliated tertiary care referral center, immediate (occurring during the procedure) and acute (occurring within 24 hours) complications of EUS were prospectively investigated. Over a first period, spanning 10 years, complications of diagnostic EUS involving 3207 consecutive patients were assessed. During the second period of 3 years, complications observed after EUS-guided fine-needle aspiration (FNA) biopsy were evaluated from 224 procedures. EUS was mostly done with the patient under sedation with intravenous propofol and spontaneous ventilation, and complications were evaluated by both the operator and the anesthesiologist.

RESULTS

There were no deaths, and no surgery was required over the two periods of assessment. Three mild complications occurred among patients who underwent standard diagnostic EUS: two immediate complications were related to anesthesia and one to the procedure. There were five complications associated with interventional EUS; all were related to the procedure (acute pancreatitis, duodenal perforation, upper digestive bleeding, cyst, and mediastinal infection), with a mean delay of occurrence of 30 hours, and mean duration of hospitalization of 7 days.

CONCLUSION

In our experience, which is the longest reported in Europe, the morbidity rates of diagnostic EUS and EUS-guided FNA biopsy were 0.093% and 2.2%, respectively, with no mortality.