Categorical working memory codes in human visual cortex
Chang Yan,
Thomas B. Christophel,
Carsten Allefeld,
John-Dylan Haynes
Affiliations
Chang Yan
Bernstein Center for Computational Neuroscience and Berlin Center for Advanced Neuroimaging and Clinic for Neurology, Charité Universitätsmedizin, corporate member of Freie Universität Berlin, Humboldt Universität zu Berlin, and Berlin Institute of Health, Berlin, Philippstraße 13, Haus 6, 10115, Germany
Thomas B. Christophel
Bernstein Center for Computational Neuroscience and Berlin Center for Advanced Neuroimaging and Clinic for Neurology, Charité Universitätsmedizin, corporate member of Freie Universität Berlin, Humboldt Universität zu Berlin, and Berlin Institute of Health, Berlin, Philippstraße 13, Haus 6, 10115, Germany; Department of Psychology, Humboldt Universität zu Berlin, Rudower Chaussee 18, Berlin, 12489, Germany; Corresponding author.
Carsten Allefeld
Department of Psychology, City, University of London, London EC1V 0HB, United Kingdom
John-Dylan Haynes
Bernstein Center for Computational Neuroscience and Berlin Center for Advanced Neuroimaging and Clinic for Neurology, Charité Universitätsmedizin, corporate member of Freie Universität Berlin, Humboldt Universität zu Berlin, and Berlin Institute of Health, Berlin, Philippstraße 13, Haus 6, 10115, Germany; Department of Psychology, Humboldt Universität zu Berlin, Rudower Chaussee 18, Berlin, 12489, Germany; Berlin School of Mind and Brain, Humboldt Universität, Berlin, Luisenstraße 56, Haus 1, Berlin, 10099, Germany; Cluster of Excellence NeuroCure, Charité Universitätsmedizin, corporate member of Freie Universität Berlin, Humboldt Universität zu Berlin, and Berlin Institute of Health, Berlin, Charitéplatz 1, Hufelandweg 14, Berlin, 10117, Germany; SFB 940 Volition and Cognitive Control, Technische Universität Dresden, Zellescher Weg 17, 01069 Dresden, Germany
Working memory contents are represented in neural activity patterns across multiple regions of the cortical hierarchy. A division of labor has been proposed where more anterior regions harbor increasingly abstract and categorical representations while the most detailed representations are held in primary sensory cortices. Here, using fMRI and multivariate encoding modeling, we demonstrate that for color stimuli categorical codes are already present at the level of extrastriate visual cortex (V4 and VO1), even when subjects are neither implicitly nor explicitly encouraged to categorize the stimuli. Importantly, this categorical coding was observed during working memory, but not during perception. Thus, visual working memory is likely to rely at least in part on categorical representations. Significance statement: Working memory is the representational basis for human cognition. Recent work has demonstrated that numerous regions across the human brain can represent the contents of working memory. We use fMRI brain scanning and machine learning methods to demonstrate that different regions can represent the same content differently during working memory. Reading out the neural codes used to store working memory contents, we show that already in sensory cortex, areas V4 and VO1 represent color in a categorical format rather than a purely sensory fashion. Thereby, we provide a better understanding of how different regions of the brain might serve working memory and cognition.
