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Thomas B. Christophel; Distributed Visual Working Memory Stores Revealed by Multivariate Pattern Analyses. Journal of Vision 2015;15(12):1407. doi: 10.1167/15.12.1407.
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Distributed Visual Working Memory Stores Revealed by Multivariate Pattern Analyses
Thomas B. Christophel, Chang Yan, Carsten Allefeld & John-Dylan Haynes
The storage buffers retaining visual working memory contents were originally postulated to reside in prefrontal cortex. Recently, a dissenting view has evolved claiming that working memory content depends on distributed storage in sensory brain regions. We provide strong evidence for this claim in a series of fMRI experiments investigating the content-specificity of delay-period activity using multivariate pattern analyses. Representations of color and motion patterns as well as complex shapes were identified in early visual, and lateral occipital posterior parietal cortex, but also in the frontal eye fields. A meta-analysis of content-specificity within these brain areas revealed large inter-areal differences critically depending on whether the stimuli were smooth global patterns or shapes with clear edges and on whether stimuli varied across color, luminance or motion direction dimensions. In addition, we show that areas beyond early visual cortex retain information in an inherently view-independent format and that coding of a given stimulus in higher visual areas is not solely driven by the visual display originally shown. Instead, the representation changes when a subject mentally transforms what they are holding in mind (i.e. during mental rotation). Extending our findings on visual working memory, we show that verbal content (Chinese Characters memorized by native speakers of Chinese) is selectively stored in prefrontal areas, more specifically Broca’s area and articulatory premotor cortex. Finally, while working memory storage seems to be represented in a distributed way, working memory control could be traced to dorsolateral prefrontal cortex regardless of what content was memorized.
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