Invariant Visual Representation by Single Neurons in the Human Brain The Medial Temporal Lobe 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 . - Neurons in the human medial temporal lobe (MTL) fire selectively to images of faces, animals, objects, or scenes - These findings 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. Study: · The subjects were eight patients with pharmacologically intractable epilepsy who had been implanted with depth electrodes to localize the focus of seizure onset. · Researchers analyzed responses of neurons from the medical temporal lobe structures: hippocampus, amygdala, entorhinal cortex and parahippocampal gyrus to images shown on a laptop commuter - Stimuli were different pictures of individuals, animals, objects, and landmark buildings presented for one second · Previous findings demonstrated the surprising degree of invariance in the neuron's firing behaviour - Ex .: One image responded only to different images of Bill Clinton - These findings suggest that neurons might encode an abstract representation of an individual. · The current paper asks whether MTL neurons can represent high-level information in an abstract manner characterized by invariance to the metric characteristics of the images · Invariance means that the unit is activated mainly by different pictures of a given individual, landmark, or object
Findings of Current Study: . There was a unit in the left posterior hippocampus; this unit fired to all pictures of Jennifer Anniston, but not (or if so, very weakly) to other famous and non-famous faces, landmarks, animals, and objects . This unit did NOT respond to pictures of Jennifer Anniston and Brad Pitt · It is unlikely that these responses were obtained by chance b 10 9 8 7 6 Number of spikes 5 2 1 0 10 20 30 40 50 Picture number 60 70 Figure 1 | A single unit in the left posterior hippocampus activated exclusively by different views of the actress Jennifer Aniston. 80 · There was another response from a single unit located in the right anterior hippocampus of a different patient, and this unit was selectively activated by pictures of Halle Berry, as well as drawings of her, as well as the letter string "Halle Berry"; also images of Halle dressed as Catwoman . These findings go beyond the common visual features of different stimuli
b 22 20 18 16 14 12 Number of spikes 10 8 6 4 2 0 10 20 30 40 50 60 70 80 90 Picture number Figure 2 | A single unit in the right anterior hippocampus that responds to pictures of the actress Halle Berry (conventions as in Fig. 1). a-c, Strikingly, this cell also responds to a drawing of her, to herself dressed as Catwoman (a recent movie in which she played