The movie "MEMENTO", help with question?

In neurobiological terms, a memory is a stored pattern of links between nerve cells in the brain. It is created when synapses in a network of neurons are activated for a short time. The more often the memory is recalled afterwards, the more likely it is that permanent links develop between the nerve cells -- and the pattern will be stored as a long-term memory. In theory, there are so many possible links that an almost unlimited number of memories can be permanently stored. Leonard's ability to have this normal, neurobiological network of implanted permanent memories has been destroyed due to his traumatic head injury. Leonard must now rely on handwritten notes, instant Polaroid snap-shots and tatoos--of all things. This artificial but tangible and objective network that he has created has replaced the natural networkng process in his brain.