The concept was simple: using digital pictures and audio to archive an experience like a weekend visit from the grandchildren, creating a summary of the resulting content by picking crucial images, and reviewing them periodically to awaken and strengthen the memory of the event.

The hardware is a little black box called the Sensecam, which contains a digital camera and an accelerometer to measure movement. Worn like a pendant around the neck, it was developed at Microsoft’s research lab in Cambridge, England.

Vicon, a British company that has licensed the technology, wants to market it to young people interested in logging their lives and posting the results to Web sites like Facebook and YouTube. For the elderly, though, it could herald a new kind of relationship between mind and machine: even as plaque gets deposited on the brain, everyday experience is deposited on silicon, then retrieved.

And what is memory? What does it all come down to? It is the movement of information over time.