Here are two accounts of exactly the same dream occurring in two different people-though they happen to be twins. In one case the dream occurred to the two persons on the same night and we have some sort of objective testimony as to the content of that dream: it was about frantically looking for important ‘papers'. Apparently the two dreamers (who were in different rooms) were talking in their sleep about the need to find important papers. Two different people verified that that is what the dreamers were sleep-talking about.
These kinds of dream phenomena are not unusual for twins. If you speak to virtually any pair of twins about this sort of thing they will often recount similarly amazing stories. Who knows if the stories are true? As far as I know there has never been an objective scientific study of these sorts of dreams in twins. Indeed there has hardly been any research at all on content of twin dreams. This is a remarkable lacuna in dream research. Given the fact that if we had good longitudinal studies of dream content in even a few twin-pairs we could learn a great deal about the genetics of dreaming it seems remarkable to me that no such study has yet been accomplished.
The ideal study of dreams in twins would collect series of dreams over months to years in as many twin pairs as possible. Comparisons would be between dream series of identical twin pairs versus dream series of fraternal twin pairs versus dream series of non-twin pairs like best friends or married couples. Would the content of dreams be more similar for identicals versus fraternals versus non-twins? Probably yes.
Let's say that what many twins report regarding their dream lives is true: some twins occasionally believe that they experience the exact same dream on the same night. How can this fact be explained? Maybe the twins had very similar experiences that day so it would not be surprising that they similar dreams that night. But the claim here is that the dreams are more than just ‘similar' in content. They are sometimes exactly the same. In addition, some twins sometimes claim that there is no way that the dream content could have come from similar experiences as the dream content referred to no such experiences and the twins lived in different cities or haven't talked for months etc
Could the ‘same dream-two people' phenomenon be due to the genetic links between the twins? The same genetic endownment would build a very similar brain and the brain in turn would produce very similar dreams and sometimes those dreams must seem very similar to the dreamers when they compare notes. But this explanation would require us to believe that the brain rigidly produces content regardless of daily input and that each type of brain produces a particular type of content etc While all that is possible I know of no theory of brain or Mind that could easily accommodate such a view.
In short, if twins do have these sorts of dreams they are still a mystery for science. I would love to hear from twins on their dreams.