Grandmother cell

The grandmother cell is a hypothetical neuron that represents a person's grandmother or, more generally, any complex and specific concept or object. A grandmother cell activates when a person "sees, hears, or otherwise sensibly discriminates" his or her grandmother. The grandmother cell theory requires a single neuron for every concept or object, as opposed to the Distributed representation theory. The grandmother cell hypthoesis is not universally accepted and in the 1980s David H. Hubel said "It's very hard to take the grandmother cell theory seriously."

In 2005, a UCLA and Caltech study found evidence of different grandmother cells that represent people like Bill Clinton or Jennifer Aniston. A neuron for Halle Berry, for example, would respond "to the concept, the abstract entity, of Halle Berry", and would fire not only for images of Halle Berry, but also to the actual name "Halle Berry". . However, there is no suggestion in that study that only the cell being monitored responded to that concept, nor was it suggested that no other actress would cause that cell to respond (although several other presented images of actress did not cause it to respond). See Quiroga et al 2005 (Nature Vol 453, pp1102–1107).

The term grandmother cell was coined by Jerry Lettvin to parody the concept, in the "role of straw man or foil for a discussion of ensemble or coarse coding theories of sensory representation." The arguments against the concept include:
 * 1) In principle one would need thousands of cells for each face, as any given face must be recognised from many different angles - profile, 3/4 view, full frontal, from above etc.
 * 2) Rather than becoming more and more specific as visual processing proceeds from retina through the different visual centres of the brain, the image is in fact dissected into even more basic features such as vertical lines, colour, speed etc., distributed in various modules separated by relatively large distances. How all these disparate features are re-integrated to form a seamless whole is known as the binding problem.
 * 3) The concept does not conform to the common experience of human memory, its function, and its malfunctions; Lettvin told the parable of how the hypothetical neurosurgeon A. Akakhievitch "ablated all of the mother cells in Portnoy's brain. As a result, Portnoy completely lost the concept of his mother"

Grandmother cells are similar to the gnostic unit or gnostic cell proposed by Jerzy Konorski.