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Published July 9, 2018 | Accepted Version + Supplemental Material
Journal Article Open

Encoding of target detection during visual search by single neurons in the human brain


Neurons in the primate medial temporal lobe (MTL) respond selectively to visual categories such as faces, contributing to how the brain represents stimulus meaning. However, it remains unknown whether MTL neurons continue to encode stimulus meaning when it changes flexibly as a function of variable task demands imposed by goal-directed behavior. While classically associated with long-term memory, recent lesion and neuroimaging studies show that the MTL also contributes critically to the online guidance of goal-directed behaviors such as visual search. Do such tasks modulate responses of neurons in the MTL, and if so, do their responses mirror bottom-up input from visual cortices or do they reflect more abstract goal-directed properties? To answer these questions, we performed concurrent recordings of eye movements and single neurons in the MTL and medial frontal cortex (MFC) in human neurosurgical patients performing a memory-guided visual search task. We identified a distinct population of target-selective neurons in both the MTL and MFC whose response signaled whether the currently fixated stimulus was a target or distractor. This target-selective response was invariant to visual category and predicted whether a target was detected or missed behaviorally during a given fixation. The response latencies, relative to fixation onset, of MFC target-selective neurons preceded those in the MTL by ∼200 ms, suggesting a frontal origin for the target signal. The human MTL thus represents not only fixed stimulus identity, but also task-specified stimulus relevance due to top-down goal relevance.

Additional Information

© 2018 Elsevier. Received: February 5, 2018. Revised: April 3, 2018. Accepted: April 27, 2018. Published: June 14, 2018. We thank all patients for their participation, Juan Xu for creating the array item labels, and Ming Jiang for helping with the analyses. This research was supported by the Rockefeller Neuroscience Institute, the Autism Science Foundation and the Dana Foundation (to S.W.), the Simons Foundation (Simons Collaboration on the Global Brain Award 543015SPI to R.A.), an NSF CAREER award (1554105 to U.R.), and the NIMH (R01MH110831 to U.R. and Conte Center P50MH094258 to R.A.). The funders had no role in study design, data collection/analysis, decision to publish, or preparation of the manuscript. Author Contributions: S.W., R.A., and U.R. designed experiments and wrote the paper. S.W., A.N.M., and U.R. performed research. S.W. and U.R. analyzed data. All authors discussed the results and contributed toward the manuscript. The authors declare no competing interests.

Attached Files

Accepted Version - nihms-1516799.pdf

Supplemental Material - mmc1.pdf


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