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Published September 3, 2008 | Published + Supplemental Material
Journal Article Open

Latency and Selectivity of Single Neurons Indicate Hierarchical Processing in the Human Medial Temporal Lobe

Abstract

Neurons in the temporal lobe of both monkeys and humans show selective responses to classes of visual stimuli and even to specific individuals. In this study, we investigate the latency and selectivity of visually responsive neurons recorded from microelectrodes in the parahippocampal cortex, entorhinal cortex, hippocampus, and amygdala of human subjects during a visual object presentation task. During 96 experimental sessions in 35 subjects, we recorded from a total of 3278 neurons. Of these units, 398 responded selectively to one or more of the presented stimuli. Mean response latencies were substantially larger than those reported in monkeys. We observed a highly significant correlation between the latency and the selectivity of these neurons: the longer the latency the greater the selectivity. Particularly, parahippocampal neurons were found to respond significantly earlier and less selectively than those in the other three regions. Regional analysis showed significant correlations between latency and selectivity within the parahippocampal cortex, entorhinal cortex, and hippocampus, but not within the amygdala. The later and more selective responses tended to be generated by cells with sparse baseline firing rates and vice versa. Our results provide direct evidence for hierarchical processing of sensory information at the interface between the visual pathway and the limbic system, by which increasingly refined and specific representations of stimulus identity are generated over time along the anatomic pathways of the medial temporal lobe.

Additional Information

© 2008 Society for Neuroscience. Received April 15, 2008; revised June 23, 2008; accepted July 12, 2008. This work was supported by the European Commission (Marie Curie Outgoing International Fellowship 040445), National Institute of Neurological Disorders and Stroke, Defense Advanced Research Projects Agency, the Engineering and Physical Science Research Council, and the Mathers Foundation. We thank all patients for their participation, and Eric Behnke, Tony Fields, Emily Ho, Eve Isham, Kelsey Laird, Neel Parikshak, and Anna Postolova for technical assistance.

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