Cited by 294Neural and Behavioral Psychology StudiesNeural dynamics and brain functionMemory and Neural Mechanisms

The DOI matches its Crossref record; 51 of the 52 references it cites were found in a registry or an index; none of the 59 sources its claims cite is checked for support yet.

A reservoir of time constants for memory traces in cortical neurons

Open access

Abstract

According to reinforcement learning theory of decision making, reward expectation is computed by integrating past rewards with a fixed timescale. In contrast, we found that a wide range of time constants is available across cortical neurons recorded from monkeys performing a competitive game task. By recognizing that reward modulates neural activity multiplicatively, we found that one or two time constants of reward memory can be extracted for each neuron in prefrontal, cingulate and parietal cortex. These timescales ranged from hundreds of milliseconds to tens of seconds, according to a power law distribution, which is consistent across areas and reproduced by a 'reservoir' neural network model. These neuronal memory timescales were weakly, but significantly, correlated with those of monkey's decisions. Our findings suggest a flexible memory system in which neural subpopulations with distinct sets of long or short memory timescales may be selectively deployed according to the task demands.

Overview

AI snapshot

Written from the paper’s full text.

TL;DR

Cortical neurons recorded from monkeys playing a competitive game carry reward-memory traces with a wide range of time constants, distributed as a power law across ACCd, DLPFC, and LIP. A reservoir network model operating near criticality reproduces this distribution, and neural timescales are weakly but significantly correlated with behavioral timescales.

Key findings

  • Across 681 neurons from ACCd (154), DLPFC (322), and LIP (205), reward memory was best fit by a single exponential for 269 neurons, double exponentials for 268 neurons, and no memory for 144 neurons; 79% (537/681) showed exponential decay.
  • Memory timescales ranged from hundreds of milliseconds to tens of seconds and followed a power-law distribution with exponent −2, consistent across the three cortical areas; about 20% of neurons (133/681) had timescales larger than one trial (29% ACCd, 19% DLPFC, 13% LIP, χ²-test p=0.0005).
  • Behavioral timescales from a reinforcement learning fit also followed a power law, and neural and behavioral timescales were weakly but significantly correlated across sessions (R=0.12, p=0.003); simultaneously recorded neuron pairs showed no significant correlation (312 pairs, R=0.07, p=0.2).
  • A randomly connected reservoir network model reproduced the power-law distribution of timescales when operating at the critical point, with exponentially distributed amplitudes and normal connection matrix.

Methods

  • Single-unit activity was recorded from six rhesus monkeys performing a matching pennies task; firing rates were computed in twelve 250-ms epochs per trial, and reward history up to five trials back was used.
  • Memory traces were estimated with multiple linear regression, then fit with single or double exponential functions multiplied by the epoch code; model selection used Bayesian Information Criterion, and reshuffling trials served as a control (96%, 656/681, showed no memory after reshuffling).
  • Behavior was fit per session with a standard reinforcement learning model using maximum likelihood, with significance assessed against 100 reshuffled surrogate sessions; the network model used 1,000 neurons with dynamics dv/dt = J·v(t) + h·Rew(t).

Limitations

  • The paper states that the matching pennies task does not necessarily require reward memory, that the neural–behavioral correlation is weak and might be caused by unknown factors, that the neuronal and behavioral ranges differ, and that behavioral data were not fit with a multi-timescale RL model.
  • The paper also states that the network model is linear and would need nonlinearities if connection-width exceeds the critical level, and that the readout driving behavior is not explicitly modeled.
  • Evident from the text: only about two neurons were simultaneously recorded on average, limiting pairwise analyses, and the study reports correlational rather than causal links between neural timescales and behavior.

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Integrity signals

Registry

Crossref · 10.1038/nn.2752

Cites

51 of 51 references verified0 citation errors · 0 not checkable

Statistics

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Verification

Claims the paper makes

0 of 59 cited sources checked · 0 supported · 0 flagged

Show all 52 claims

  • It may state two separate claims as one. 26
  • Probably not a substantial claim. 31
50 of 50
  • The paper relies on this without support.

    The neural mechanism underlying switching between long and short time constants for computing reward expectation remains poorly understood.

    “The neural mechanism underlying switching between long and short time constants for computing reward expectation remains poorly understood.”
  • The paper relies on this without support.

    The neural mechanisms responsible for such timescales are still unknown.

    “but the neural mechanisms responsible for such timescales are still unknown.”
  • The paper relies on this without support.

    The matching pennies task used in this study does not necessarily require the memory of past rewards, and the optimal strategy for the monkey is to choose randomly and unpredictably.

    “The matching pennies task used in this study does not necessarily require the memory of past rewards, and the optimal strategy for the monkey is to choose randomly and unpredictably.”
  • The authors state this as an assumption.

    The effects of rewards in successive trials are additive.

    “assuming that the effects of rewards in successive trials are additive.”
  • The authors state this as an assumption.

    The memory trace f is factorized into the epoch code g(k) and an exponential function ex(t).

    “we assumed that the memory trace f is factorized into the epoch code g(k) and an exponential function ex(t)”
  • The authors state this as an assumption.

    The specific form of the input signals is not important; the results depend only on the synaptic matrix J.

    “For our purposes, the specific form of the input signals is not important; the results will depend only on the synaptic matrix J.”
  • The authors state this as an assumption.

    The connection weights (entries of matrix J) are randomly distributed.

    “We assumed the connection weights (the entries of the matrix J) to be randomly distributed”
  • The authors state this as an assumption.

    The linear model is sufficient for reproducing the observed power-law distribution of timescales under specific conditions.

    “here we limit ourselves to the linear model, which is sufficient for the purpose of reproducing the observed power-law distribution of timescales under specific conditions.”
  • The authors state this as an assumption.

    Memory traces are exponential functions ex(t) rescaled by the epoch code g(k).

    “we assumed that memory traces are exponential function ex(t) rescaled by the epoch code g(k)”
  • The authors state this as an assumption.

    The saccade reaction time of the animal in all trials is equal to 120 ms on average.

    “we assumed that the saccade reaction time of the animal in all trials is equal to 120ms (average)”
  • The authors state this as an assumption.

    The time elapsed between the initiation of two successive trials is 3.4 s (median).

    “and that the time elapsed between the initiation of two successive trials is 3.4s (median).”
  • The paper relies on this without support.

    The sequence of rewards is nearly random.

    “Because the sequence of rewards is nearly random and N is large, different columns of the matrix Rew are nearly orthogonal.”
  • The paper relies on this without support.

    In the matching pennies task, the global optimal strategy is to choose randomly and therefore does not require memory.

    “Although the global optimal strategy for the matching pennies task is to choose randomly and therefore does not require memory, the animals made their decisions largely on the basis of their reward history11,19-22.”
13 of 13

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Metadata

Authors
Bernacchia, A., Seo, H., Lee, D., & Wang, X.-J.
Affiliations
Yale University (US)
Corresponding author
Wang, Xiao-Jing
Venue
Nature Neuroscience
Published
2011-02-13
Volume
14
Issue
3
Pages
366-372
ISSN
  • 1097-6256 (ISSN-L)
  • 1546-1726
OpenAlex
W2139630667
Cited by
292
References
52
Citations by year
2026: 14 · 2025: 13 · 2024: 19 · 2023: 15 · 2022: 23 · 2021: 25 · 2020: 28 · 2019: 19 · 2018: 21 · 2017: 21 · 2016: 16 · 2015: 20 · 2014: 18 · 2013: 15 · 2012: 16
FWCI
9.41
Type
journal article
Language
en
Open access
Locations
  • Nature Neuroscience (publishedVersion)
  • PubMed (publishedVersion)
  • PubMed Central (acceptedVersion)
Funders
  • National Institute of Mental Health (R01MH062349, R01MH073246)
  • National Institute on Drug Abuse (DA029330, R01DA029330)
Topics
  • Life Sciences › Neuroscience › Cognitive Neuroscience › Neural and Behavioral Psychology Studies
  • Life Sciences › Neuroscience › Cognitive Neuroscience › Neural dynamics and brain function
  • Life Sciences › Neuroscience › Cognitive Neuroscience › Memory and Neural Mechanisms
Keywords
reward memory, power-law distribution, reinforcement learning, decision-making, prefrontal cortex, cingulate cortex, parietal cortex, reward anticipation, decision time, cortical neurons
MeSH terms
Animals, Haplorhini, Cerebral Cortex, Decision Making, Humans, Memory, Nerve Net, Neurons, Neuropsychological Tests, Reinforcement, Psychology, Reward, Time Factors

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