Revisiting grandmother cells

Recent work by R. Q. Quiroga’s group, ‘Explicit Encoding of Multimodal Percepts by Single Neurons in the Human Brain’ in Current Biology, has looked at how we remember people, places and categories. The paper’s abstract is below:

“Different pictures of Marilyn Monroe can evoke the same percept, even if greatly modified as in Andy Warhol’s famous portraits. But how does the brain recognize highly variable pictures as the same percept? Various studies have provided insights into how visual information is processed along the “ventral pathway,” via both single-cell recordings in monkeys and and functional imaging in humans and. Interestingly, in humans, the same “concept” of Marilyn Monroe can be evoked with other stimulus modalities, for instance by hearing or reading her name. Brain imaging studies have identified cortical areas selective to voices and and visual word forms and. However, how visual, text, and sound information can elicit a unique percept is still largely unknown. By using presentations of pictures and of spoken and written names, we show that (1) single neurons in the human medial temporal lobe (MTL) respond selectively to representations of the same individual across different sensory modalities; (2) the degree of multimodal invariance increases along the hierarchical structure within the MTL; and (3) such neuronal representations can be generated within less than a day or two. These results demonstrate that single neurons can encode percepts in an explicit, selective, and invariant manner, even if evoked by different sensory modalities.”

This sounds a lot like grandmother cells to me. Here we have pathways starting with different sensory modalities and going through separate perceptual processes leading ultimately to the same cell in the memory apparatus of the hippocampus. Is this not the neural instantiation of our knowing people, places and abstract concepts? Are these not grandmother cells – a neuron that can be activated by any activity the would amount to a definition of my grandmother and in turn activate attributes of my grandmother missing from the original activity? A photograph of her face brings to mind the sound of her singing.

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