  We expose first a biological model of memory based on one hand of the
mechanical oscillations of axons during action potential and on the other hand
on the changes in the extra cellular matrix composition when a mechanical
strain is applied on it. Due to these changes, the stiffness of the extra
cellular matrix along the most excited neurons will increase close to these
neurons due to the growth of astrocytes around them and to the elastoplastic
behavior of collagen. This will create preferential paths linked to a memory
effect. In a second part, we expose a physical model based on random walk of
the action potential on the array composed of dendrites and axons. This last
model shows that repetition of the same event leads to long time memory of this
event and that paradoxical sleep leads to the linking of different events put
into memory.
