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Neuronal correlates of parametric working memory in the prefrontal cortex

Nature volume 399, pages 470–473 (1999)Cite this article

Abstract

Humans and monkeys have similar abilities to discriminate the difference in frequency between two mechanical vibrations applied sequentially to the fingertips1,2,3. A key component of this sensory task is that the second stimulus is compared with the trace left by the first (base) stimulus, which must involve working memory. Where and how is this trace held in the brain? This question was investigated by recording from single neurons in the prefrontal cortex of monkeys while they performed the somatosensory discrimination task. Here we describe neurons in the inferior convexity of the prefrontal cortex whose discharge rates varied, during the delay period between the two stimuli, as a monotonic function of the base stimulus frequency. We describe this as ‘monotonic stimulus encoding’, and we suggest that the result may generalize: monotonic stimulus encoding may be the basic representation of one-dimensional sensory stimulus quantities in working memory. Thus we predict that other behavioural tasks that require ordinal comparisons between scalar analogue stimuli would give rise to monotonic responses similar to those reported here.

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Figure 1: Discrimination task.
Figure 2: Monotonic responses during the delay period.
Figure 3: Neuronal response types.

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Acknowledgements

The research of R.R. was partially supported by an International Research Scholars Award from the Howard Hughes Medical Institute and grants from DGAPA-UNAM, CONA-CyT and Fundación Miguel Alemán A.C. We thank W. Newsome, M. Shadlen, their research groups, and V.Mountcastle and E. Salinas for extensive comments and discussion; A. Zainos for help during the experiments; and F. Jandete and S. Méndez for technical assistance. R.R. conceived the experiment, and together with A.H. and L.L. carried it out; C.D.B. designed and carried out the data analysis; R.R. and C.D.B. co-wrote the paper.

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Authors and Affiliations

  1. Instituto de Fisiología Celular, Universidad Nacional Autonáma de México, México D.F., 04510, México

    Ranulfo Romo, Carlos D. Brody, Adrián Hernández & Luis Lemus

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  1. Ranulfo Romo
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  2. Carlos D. Brody
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  3. Adrián Hernández
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  4. Luis Lemus
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Correspondence to Ranulfo Romo.

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Romo, R., Brody, C., Hernández, A. et al. Neuronal correlates of parametric working memory in the prefrontal cortex. Nature 399, 470–473 (1999). https://doi.org/10.1038/20939

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