How Many Neurons Does It Take to See a Picture?
Israeli scientists publishing in Current Biology1 attempted to determine how many neurons participate in the representation of a single image. At least a million was their conservative answer: probably more like 30 or 300 million or more. They made careful measurements of neural activity when subjects were shown a face or a house. In the brain, there are about 60,000 neurons per cubic millimeter, each joined to hundreds of neighboring neurons in complex ways.
1Levy, Hassan and Malach, “One Picture Is Worth At Least a Million Neurons,” Current Biology, Vol 14, 996-1001, 8 June 2004.
Remember that their answer was a minimum; they seemed overly cautious to err on the conservative side. And this was for simple, stationary images. Undoubtedly many more neurons are firing constantly in our usually complex, moving field of view. Each eye has about 120 megapixel resolution (see 07/13/2001 headline), and complex image processing takes place in the eye before the neurons receive the data (see 05/22/2003 headline).