1. Computation and Neural Systems, California Institute of Technology, Pasadena, California 91125, USA
2. Division of Neurosurgery and Neuropsychiatric Institute, University of California, Los Angeles (UCLA), California 90095, USA
3. Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02142, USA
4. Functional Neurosurgery Unit, Tel-Aviv Medical Center and Sackler Faculty of Medicine, Tel-Aviv University, Tel-Aviv 69978, Israel
5. †Present address: Department of Engineering, University of Leicester, LE1 7RH, UK

Correspondence to: R. Quian Quiroga^1,2,5 Correspondence and request for materials should be addressed to R.Q.Q. (Email: rodri@vis.caltech.edu).

It takes a fraction of a second to recognize a person or an object even when seen under strikingly different conditions. How such a robust, high-level representation is achieved by neurons in the human brain is still unclear^{1, 2, 3, 4, 5, 6}. In monkeys, neurons in the upper stages of the ventral visual pathway respond to complex images such as faces and objects and show some degree of invariance to metric properties such as the stimulus size, position and viewing angle^{2, 4, 7, 8, 9, 10, 11, 12}. We have previously shown that neurons in the human medial temporal lobe (MTL) fire selectively to images of faces, animals, objects or scenes^{13, 14}. Here we report on a remarkable subset of MTL neurons that are selectively activated by strikingly different pictures of given individuals, landmarks or objects and in some cases even by letter strings with their names. These results suggest an invariant, sparse and explicit code, which might be important in the transformation of complex visual percepts into long-term and more abstract memories.

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