Human single-neuron responses at the threshold of conscious recognition

doi:10.1073/pnas.0707043105

Human single-neuron responses at the threshold of conscious recognition

*Department of Engineering, University of Leicester, Leicester LE1 7RH, United Kingdom;
^†Division of Neurosurgery, David Geffen School of Medicine and Semel Institute for Neuroscience and Human Behavior, University of California, Los Angeles, CA 90095;
^‡Department of Psychology, Claremont Graduate University, Claremont, CA 91711;
^§Neurobiology Department, Weizmann Institute of Science, Rehovot 76100, Israel; and
^¶Functional Neurosurgery Unit, Tel-Aviv Medical Center and Sackler Faculty of Medicine, Tel-Aviv University, Ramat Aviv Tel Aviv 69978, Israel

Edited by Richard A. Andersen, California Institute of Technology, Pasadena, CA, and approved January 4, 2008 (received for review July 26, 2007)

Abstract

We studied the responses of single neurons in the human medial temporal lobe while subjects viewed familiar faces, animals, and landmarks. By progressively shortening the duration of stimulus presentation, coupled with backward masking, we show two striking properties of these neurons. (i) Their responses are not statistically different for the 33-ms, 66-ms, and 132-ms stimulus durations, and only for the 264-ms presentations there is a significantly higher firing. (ii) These responses follow conscious perception, as indicated by the subjects' recognition report. Remarkably, when recognized, a single snapshot as brief as 33 ms was sufficient to trigger strong single-unit responses far outlasting stimulus presentation. These results suggest that neurons in the medial temporal lobe can reflect conscious recognition by “all-or-none” responses.

Footnotes

^‖To whom correspondence should be addressed. E-mail: ifried{at}mednet.ucla.edu
Author contributions: R.Q.Q., R. Mukamel, R. Malach, and I.F. designed research; R.Q.Q., R. Mukamel, E.A.I., and I.F. performed research; R.Q.Q. analyzed data; and R.Q.Q. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
This article contains supporting information online at www.pnas.org/cgi/content/full/0707043105/DC1.