Working Memory: Separating the present and the future

The brain stores information that is needed immediately and information that will be needed in the future in different ways.
  1. Qing Yu  Is a corresponding author
  2. Bradley R Postle  Is a corresponding author
  1. University of Wisconsin-Madison, United States

Imagine you are in a grocery store without a shopping list. Even though you need to purchase multiple items, you still need to select them one by one. How does the brain distinguish between the most relevant information from everything else on our mind? In particular, is information about the item you intend to buy first stored in your 'working memory' in the same way as information about the other items?

A common method used to study memory processing in the human brain is functional magnetic resonance imaging (fMRI). Moreover, researchers often use machine learning techniques, such as multivariate pattern analysis, to decode information from the fMRI data. Typically, if multivariate pattern analysis is able to discriminate between different pieces of information based on their activity patterns in the brain, this is interpreted as evidence for an 'active' representation of the information. Alternatively, a failure to decode might suggest there is no active representation of it.

It is generally acknowledged that information that is immediately relevant is actively represented in working memory, but it remains unclear if this is also true for information that will be needed in the future (that is, for prospectively relevant information: see, for example, LaRocque et al., 2013; Lewis-Peacock et al., 2012). One possibility is that the latter is stored in an ‘activity-silent’ manner, due to a transient change in the strength of the synaptic connections between neurons (see, for example, Barak and Tsodyks, 2014). Such information can usually not be detected by traditional fMRI measurements, unless the network is stimulated to reactivate the ‘activity-silent’ information (Rose et al., 2016; Wolff et al., 2017). Alternatively, prospectively relevant information may be transferred to brain regions that are different from those where immediately relevant information is held (see, for example, Christophel et al., 2018).

Now, in eLife, Christian Olivers and colleagues of the Vrije Universiteit Amsterdam and the University of Amsterdam – Anouk van Loon, Katya Olmos Solis and Johannes Fahrenfort – report evidence for a third possibility, namely that prospectively relevant information is represented actively, but in a recoded format (van Loon et al., 2018).

To explore how working memory distinguishes between immediately relevant and prospectively relevant information, volunteers were asked to perform two visual search tasks. In the first experiment, they consecutively viewed a flower and another object (either a cow, a dresser or a skate), and the order was manipulated between trials. A cue during the initial presentation indicated which image would be relevant for the first (imminent) or the second (prospective) search. Then, depending on the trial (current vs. prospective), they had to first search for the target flower in an array of flowers and then search for the other target (e.g., a cow in an array of different cows), or vice versa. During the tasks, the researchers used fMRI to measure a region of the brain involved in categorizing objects, called the posterior fusiform cortex.

The researchers found that before the volunteers knew which of the two images would be the first search target, both were actively represented in a similar way in working memory. However, once one of the images was designated as immediately relevant, the representations diverged. Although both were still actively represented, the patterns of the two stimuli were the inverse of each other, as indicated by multivariate pattern analysis and another technique called representational dissimilarity analysis.

Moreover, after the first search, when the prospectively relevant information became immediately relevant, its representation in the brain 'flipped' back to its original pattern. In a second experiment, the researchers found that this reversed pattern only happened if the information was prospectively relevant; if the volunteer was told that the information was no longer relevant, it was lost from working memory.

As van Loon et al. acknowledge, other research groups have made similar discoveries using different kinds of tasks and different kinds of stimuli. Together all these results have important implications for our understanding of the representation of information in working memory. Therefore, a key goal for future research will be to clarify the circumstances under which prospectively relevant information is re-represented – relative to immediately relevant information – in a different pattern, in a different region of the brain, or a different state.

References

Article and author information

Author details

  1. Qing Yu

    Qing Yu is in the Department of Psychiatry, University of Wisconsin-Madison, Madison, United States

    For correspondence
    qyu55@wisc.edu
    Competing interests
    No competing interests declared
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0001-8480-7634
  2. Bradley R Postle

    Bradley R Postle is in the Department of Psychology and the Department of Psychiatry, University of Wisconsin-Madison, Madison, United States

    For correspondence
    postle@wisc.edu
    Competing interests
    No competing interests declared
    ORCID icon "This ORCID iD identifies the author of this article:" 0000-0001-8555-0148

Publication history

  1. Version of Record published: December 4, 2018 (version 1)

Copyright

© 2018, Yu et al.

This article is distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use and redistribution provided that the original author and source are credited.

Metrics

  • 1,580
    Page views
  • 203
    Downloads
  • 1
    Citations

Article citation count generated by polling the highest count across the following sources: Crossref, PubMed Central, Scopus.

Download links

A two-part list of links to download the article, or parts of the article, in various formats.

Downloads (link to download the article as PDF)

Open citations (links to open the citations from this article in various online reference manager services)

Cite this article (links to download the citations from this article in formats compatible with various reference manager tools)

  1. Qing Yu
  2. Bradley R Postle
(2018)
Working Memory: Separating the present and the future
eLife 7:e43339.
https://doi.org/10.7554/eLife.43339
  1. Further reading

Further reading

    1. Neuroscience
    Yonatan Sanz Perl, Sol Fittipaldi ... Enzo Tagliazucchi
    Research Article

    The treatment of neurodegenerative diseases is hindered by lack of interventions capable of steering multimodal whole-brain dynamics towards patterns indicative of preserved brain health. To address this problem, we combined deep learning with a model capable of reproducing whole-brain functional connectivity in patients diagnosed with Alzheimer’s disease (AD) and behavioral variant frontotemporal dementia (bvFTD). These models included disease-specific atrophy maps as priors to modulate local parameters, revealing increased stability of hippocampal and insular dynamics as signatures of brain atrophy in AD and bvFTD, respectively. Using variational autoencoders, we visualized different pathologies and their severity as the evolution of trajectories in a low-dimensional latent space. Finally, we perturbed the model to reveal key AD- and bvFTD-specific regions to induce transitions from pathological to healthy brain states. Overall, we obtained novel insights on disease progression and control by means of external stimulation, while identifying dynamical mechanisms that underlie functional alterations in neurodegeneration.

    1. Neuroscience
    Andrea Alamia, Lucie Terral ... Rufin VanRullen
    Research Article Updated

    Previous research has associated alpha-band [8–12 Hz] oscillations with inhibitory functions: for instance, several studies showed that visual attention increases alpha-band power in the hemisphere ipsilateral to the attended location. However, other studies demonstrated that alpha oscillations positively correlate with visual perception, hinting at different processes underlying their dynamics. Here, using an approach based on traveling waves, we demonstrate that there are two functionally distinct alpha-band oscillations propagating in different directions. We analyzed EEG recordings from three datasets of human participants performing a covert visual attention task (one new dataset with N = 16, two previously published datasets with N = 16 and N = 31). Participants were instructed to detect a brief target by covertly attending to the screen’s left or right side. Our analysis reveals two distinct processes: allocating attention to one hemifield increases top-down alpha-band waves propagating from frontal to occipital regions ipsilateral to the attended location, both with and without visual stimulation. These top-down oscillatory waves correlate positively with alpha-band power in frontal and occipital regions. Yet, different alpha-band waves propagate from occipital to frontal regions and contralateral to the attended location. Crucially, these forward waves were present only during visual stimulation, suggesting a separate mechanism related to visual processing. Together, these results reveal two distinct processes reflected by different propagation directions, demonstrating the importance of considering oscillations as traveling waves when characterizing their functional role.