Neuron Culture

One of my favorite Roz Chast cartoons shows a woman dumping out the high-falutin' contents of a filing cabinet drawer — 16th century art, or something like that — to make room for a new drawer full of information about new TV shows. This is the finite filing cabinet model of memory, in which you toss out one set of memory to make room for new information. It's not one that has had much credence in neuroscience. Memories have been considered, the last decade or so, to be in there somewhere, but perhaps just inaccessible. The old "I haven't forgotten it; I just can't recall it right now" situation.

Science New, via Wired Science, covers a paper suggesting the finite filing cabinet model may have some application after all. I'd say this needs some replication before it overturns the store-it-all paradigm; file it under "Interesting if true," and remember what I call Ioanidis's Maxim, which is that most novel findings don't prove out.

So let the testing begin. In the meantime, it's intriguing to see Roz Chast's hypothesis bolstered experimentally.

A new rodent study shows that newborn neurons destabilize established connections among existing brain cells in the hippocampus, a part of the brain involved in learning and memory. Clearing old memories from the hippocampus makes way for new learning, researchers from Japan suggest in the November 13 Cell.

Other researchers had proposed the idea that neurogenesis, the birth of new neurons, could disrupt existing memories, but the Cell paper is the first to show evidence supporting the idea, says Paul Frankland, a neuroscientist at the Hospital for Sick Children in Toronto.

Scientists have known that memories first form in the hippocampus and are later transferred to long-term storage in other parts of the brain. For some amount of time the memory resides both in the hippocampus and elsewhere in the brain. What’s not been known is how, after a few months or years, the memory is gradually cleared from the hippocampus.

Researchers have also debated the role of neurogenesis in learning and memory. The hippocampus is one of only two places in the adult brain where scientists know that new neurons form. On the basis of previous studies, many researchers think new neurons stabilize memory circuits or are somehow otherwise necessary to form new memories.

The new study suggests the opposite: Newborn neurons weaken or disrupt connections that encode old memories in the hippocampus.