Oscillatory brain state predicts variability in working memory.

N E Myers,Lena Walther,A C Nobre,M G Stokes

doi:10.1523/jneurosci.4741-13.2014

N E Myers, Lena Walther + Show 2 more

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https://doi.org/10.1523/jneurosci.4741-13.2014

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Abstract

Our capacity to remember and manipulate objects in working memory (WM) is severely limited. However, this capacity limitation is unlikely to be fixed because behavioral models indicate variability from trial to trial. We investigated whether fluctuations in neural excitability at stimulus encoding, as indexed by low-frequency oscillations (in the alpha band, 8-14 Hz), contribute to this variability. Specifically, we hypothesized that the spontaneous state of alpha band activity would correlate with trial-by-trial fluctuations in visual WM. Electroencephalography recorded from human observers during a visual WM task revealed that the prestimulus desynchronization of alpha oscillations predicts the accuracy of memory recall on a trial-by-trial basis. A model-based analysis indicated that this effect arises from a modulation in the precision of memorized items, but not the likelihood of remembering them (the recall rate). The phase of posterior alpha oscillations preceding the memorized item also predicted memory accuracy. Based on correlations between prestimulus alpha levels and stimulus-related visual evoked responses, we speculate that the prestimulus state of the visual system prefigures a cascade of state-dependent processes, ultimately affecting WM-guided behavior. Overall, our results indicate that spontaneous changes in cortical excitability can have profound consequences for higher visual cognition.

Highlights

Visual working memory (WM) allows us to maintain and manipulate visual information over brief periods of time and is critical for guiding ongoing behavior
Our results indicate that spontaneous changes in cortical excitability can have profound consequences for higher visual cognition
As we argue, prestimulus alpha power is an index of cortical excitability, it should predict the magnitude of visual responses to the memory stimulus

Summary

Introduction

Visual working memory (WM) allows us to maintain and manipulate visual information over brief periods of time and is critical for guiding ongoing behavior. The storage capacity of WM is extremely limited (Cowan, 2000), either in the quality (Bays et al, 2009; Keshvari et al, 2013) or quantity (i.e., 3– 4 items: Zhang and Luck, 2008; Luck and Vogel, 2013) of information that can be maintained. Individual differences in WM performance strongly predict higher cognitive functions such as IQ (Engle et al, 1999; Fukuda et al, 2010) and real-world performance (Gathercole et al, 2003). WM capacity may not be a static trait even within an individual. Recent studies measuring the fidelity of representations stored in WM reveal significant trial-by-trial variability within observers, both in the number of encoded items (Sims et al, 2012)

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