Hi George

This is a very good question - a case for paranormal investigation!  i've heard that their are cases of 'flash backs' especially in the more older cities like London and Jerusalem for example. 

Reincarnation works on the principle of 'what you sow you shall reap' and in taking the theory that it takes approximately 400 years between incarnations; we start a project, say in the year 1600 we come back in the year 2000 to fulfill it as society has advanced and is ready for the completion of the project - an example.

The fulfilling of the project does not rely on recalling ones past life as we bring it with us in our memory soul and the unfoldment will happen 'naturally'.

Alot can happen to the landscape and vibrations of the earth over centuries that would block the physical memory recall.  Graveyards however, are normally the best place for this recall.

But we are not meant to recall, most, of our past lifes as it would confuse our minds too much and interfere with the reason for the present life.  (Not saying that past-life regression are wrong, they can be very helpful in solving certain phobias etc. i do think hypnosis can be dangerous though)

But generally this is why we do not remember our past lifes - we would become schizophrenic and spend this life dealing with a mental problem rather than getting on with life.

I have thought it a good idea to bury something, maybe a note to oneself,  in a public park and think about this object and place every night for a minute or two - and see if in a later life if one would retrive it!