Entangled in the womb? A pilot study on the possible physiological connectedness between identical twins with different embryonic backgrounds.

Objective: Studies of synchronous physiological responses to startle stimuli between monozygotic twins and other paired subjects have suffered from methodological flaws such as post-hoc specifications of "connectedness" criteria. The mechanisms that affect any such connectedness are unknown. With the logistic and financial support of a television company, we conducted a methodological pilot study with predefined objective hit criteria in which we used four pairs of twins with frequent experiences of connectedness.

Methods: While one twin was exposed during a 12-minute period to five randomly presented mild shock or surprise stimuli, the electrodermal activity, blood pressure, breathing, and bodily movements were simultaneously recorded in the second twin. An authorized polygraph expert who was blind to the stimulus exposure times examined the data for deviations from normal physiological patterns during relaxation and delivered precisely timed estimates of such deviations. "Hits" (indications of connectedness) were objectively defined as an estimate lying within a 15-second "hit window."

Results: Overall results were nonsignificant, P > .7. However, for one pair of twins, the polygraph expert identified 10 deviating patterns, of which three were hits were P < .03. This data set was sent to a second, independent expert, who blindly identified the same three hits, pointing to only eight patterns, P < .0003.

Discussion: We argue that the applied methodology for "hit" identification is objective and recommendable. Speculatively, because the "successful" pair of twins was reported to be monochorionic-monoamnionic (as embryos, they shared the same placenta and the same bag of water), embryonic history might be further investigated as a potential factor for connectedness between monozygotic twins.