The brain is a transformer...your mind exists outside of the brain, this is why scientists can't pinpoint where memories are stored. It also explains why people suffering from serious traumatic or stroke induced brain damage can remember what it is like to be 'normal', but are no longer able to elicit the responses they want.
Consciousness exists on the quantum level, it cannot be destroyed. We are eternal as regards our consciousness.
You may say,'but I cannot remember previous existences'...well most people can't, however this is probably a blessing. We get to begin again, hopefully on a higher level, and with a clean slate. Some do however remember either through hypnosis or trance.
There is also the case of people who have seen and/or spoken with loved ones who have died. This is not an infrequent occurrence.
