From Scientific American:
A recent study indicates that our brains employ far fewer cells to interpret a given image than previously believed, and the findings could help neuroscientists determine how memories are formed and stored. In previous decades, two extreme views have emerged. One says that millions of neurons work in concert, piecing together various bits of information into one coherent picture, whereas the ot her states that the brain contains a separate neuron to recognize each individual object and person. In the 1960s neurobiologist Jerome Lettvin named the latter idea the “grandmother cell” theory, meaning that the brain has a neuron devoted just for recognizing each family member. Lose that neuron, and you no longer recognize grandma. Experts long ago dismissed this latter view as overly simplistic. But Rodrigo Quian Quiroga of the University of Leicester in England and his colleagues decided to investigate just how selective single neurons might be.
More here.