The Matrix in Your Head; June/July 2007; Scientific American Mind; by James J. Knierim; 8 Page(s)

In the 2001 suspense thriller Memento, the lead character, Lenny, suffers a brain injury that makes him unable to remember events for longer than a minute or so. This type of amnesia, known as anterograde amnesia, is well known to neurologists and neuropsychologists. Like Lenny, sufferers remember events from their life histories that occurred before their injuries, but they cannot form lasting memories of anything that occurs afterward. As far as they recall, their personal histories ended shortly before the onset of their disorders.

The cause of Lenny's problem was probably damage to his hippocampus, a pair of small, deep-brain structures crucial to memory--and also important to some of today's most exciting and consequential neuroscience research. Decades of research have made clear that the hippocampus and surrounding cortex do more than just place our life events in time. The hippocampus, along with a newly discovered set of cells known as grid cells in the nearby cortex, traces our movement through space as well. And by doing so, it supplies a rich array of information that provides a context in which to place our life's events. The picture that is emerging is of historic importance and more than a little beauty.