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14. Memory, like photographs, is a message posted forward into a future it cannot yet imagine.
Richard Powers

palimpsest, n.
1. writing material on which writing can be erased;
2. used writing material with erasures.

Within the memory centres of the brain, the codes for storing memory are transmitted along nerve cells which reach out like tendrils to other nerve cells, laying down new networks of connections. 

Memory is encoded in these new networks in the form of "engrams", the memory traces which are the supposed permanent changes in the brain accounting for the existence of memory.

But memory can be scrambled and erased, leaving only traces of the original, a neural palimpsest. New memories are encoded, new layers of memory are inscribed on this palimpsest.