GEN-ERIC News

In a study publishing in PLoS Computational Biology on September 7, 2007, they show that for realistic networks of spiking neurons, the number of memories is not proportional to the number of neurons, it’s proportional to the number of connections per neurons – at most about 10,000. Moreover, they provided evidence that the constant of proportionality is small, not more than a few percent, and they eliminated one of theorists’ favorite tricks – reducing the number of neurons involved in any one memory – for increasing that constant. Thus, if networks use the algorithm proposed by Hopfield, they can store at most about 500 memories, no matter how many neurons they contain. So we’re not exactly back to square one, but we’re not much farther than square two: we no longer know how the brain holds so many memories.