If my memory serves me correct (hic!) the famous abduction case of Barny and Betty Hill (Hampshire, USA) has some revealing items. If you recall, it was only two years after the incident that the Hills decided to do something about the physical marks on their bodies and the nightmares they were having. Both husband and wife were dreaming the same thing but didn't share it until much later, and they hadn't thought about being abducted until they underwent hypnosis. It was at the doctors office that little by little the episode was put together.
We know that hypnosis allows us to disassociate ourselves from the sensations we feel. We also know that the mind can only focus on one thing at a time. If we focus away from a traumatic experience, for example, and onto a pleasant one, the unpleasant experience is "forgotten" or relegated to a part of memory that disconnects from the nervous system that produces sensation; the pleasant experience connects to the nervous system and so our body experiences the pleasantness. It is sort of a switching of priorities that takes place in the cortex of the brain. The neocortex in humans is much larger than in animals and this allows us the ability to reorganize signals and decide to choose some and not others. Hypnotists take advantage of this fact.
But in the case of the above mentioned case, The Hills weren't even aware of the abduction until the hypnosis revealed it.
Perhaps, and this is simple conjecture, assuming extraterrestrial beings did abduct someone, because they are developed enough to travel such long distances, they would have developed some sort of tool with which to zap the memory, as it were, and relegated it into that portion of the cortex that would read the experience as secondary; in other words, they have decided the priority for us! Certainly the brain did register the experience but the "zap" would relegate it to the subconscious (in which case our sleep may be disturbed).
There was a case here in Quebec some years ago where a boy travelling along a country road on his bicycle and going to his girlfriend's place found that his girlfriend was angry when he arrived. The reason is because he arrived about two hours late from the time he said he would arrive! The story goes on to explain how the young man saw a large luminous object descending toward him and he stopped and hopped off his two wheeler. The circular-shaped object was very large and on its underbelly appeared a great luminosity that looked like an opening in which a head or two seemed to be peering down at him. The boy, in recounting this experience, remembered only that he was picking up his bike and continueing his ride to his girlfriend. It was under hypnosis that the details came out.
Assuming what the boy saw was a genuine flying saucer with extraterrestrial humanoids come from some other planet and visiting the earth, perhaps the magnetic field or some such energy emanating from the spacecraft may have had some physiological influence on the brain chemistry affecting the cortex and resulting in a switching of priorities, as explained above.
This is all conjecture, of course.
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dumaurier