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Published January 3, 2018 | Accepted Version + Supplemental Material
Journal Article Open

Single-Neuron Representation of Memory Strength and Recognition Confidence in Left Human Posterior Parietal Cortex


The human posterior parietal cortex (PPC) is thought to contribute to memory retrieval, but little is known about its specific role. We recorded single PPC neurons of two human tetraplegic subjects implanted with microelectrode arrays, who performed a recognition memory task. We found two groups of neurons that signaled memory-based choices. Memory-selective neurons preferred either novel or familiar stimuli, scaled their response as a function of confidence, and signaled subjective choices regardless of truth. Confidence-selective neurons signaled confidence regardless of stimulus familiarity. Memory-selective signals appeared 553 ms after stimulus onset, but before action onset. Neurons also encoded spoken numbers, but these number-tuned neurons did not carry recognition signals. Together, this functional separation reveals action-independent coding of declarative memory-based familiarity and confidence of choices in human PPC. These data suggest that, in addition to sensory-motor integration, a function of human PPC is to utilize memory signals to make choices.

Additional Information

© 2017 Elsevier. Received 24 July 2017, Revised 17 October 2017, Accepted 17 November 2017, Available online 14 December 2017. We thank both patients for participating in these studies and Ralph Adolphs for facilitating this collaboration through the Conte Center. This work was supported by NIH (EY015545 to R.A.A., the NIMH Conte Center at CaltechP50MH094258 to R.A.A. and U.R., and R01MH110831 to U.R.), the National Science Foundation (CAREER Award BCS-1554105 to U.R.), the T & C Chen BMI Center at Caltech, the Della Martin Foundation, and the Boswell Foundation. Data and Software Availability: The spike detection and sorting toolbox OSort was used for data processing, which is available as open source. Data and custom MATLAB analysis scripts are available upon reasonable request from Ueli Rutishauser (urut@caltech.edu). Additional Resources: This study was conducted as part of NIH clinical trial NCT01958086. Author Contributions: U.R., T.A., and R.A.A. designed the study. U.R. and T.A. collected data and analyzed the results. U.R., T.A., and R.A.A. wrote the paper. E.R.R. provided experimental facilities and administrative assistance and coordination with Casa Colina Hospital and Centers for Healthcare. N.P. performed surgery.

Attached Files

Accepted Version - nihms922234.pdf

Supplemental Material - mmc1.pdf


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