When I was a younger man I spent 13 years at 5 universities collecting and storing knowledge/memories. I'm no longer young and, quite often, the memory either fades, or fails in ready access. It feels as if those precious(and hard won) memories are much as liquid stored in a sieve. And, some days, 50 year old memories are as crisp as though they were formed yesterday. One wonders: Maybe I ain't lost any of those memories? Maybe gaining access to them is the problem? What exactly is a memory in relation to our brains? It would seem that each tiny bit of each memory would have had to have changed a cell, as it seems highly unlikely that a electrical neural impulse could last so long. This would imply that we have a finite capacity for knowledge/memories determined by the quantity of available neural cells. If we are near capacity, then do we use the neural cells that were for access to "memories" to themselves be used for memory storage?