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J Neurosci. 2014 Jul 23;34(30):9857-66. doi: 10.1523/JNEUROSCI.2758-13.2014.

A shared, flexible neural map architecture reflects capacity limits in both visual short-term memory and enumeration.

Author information

1
Center for Mind/Brain Sciences, University of Trento, I-38068 Rovereto, Italy, Department of Psychology, Humboldt University of Berlin, D-12489 Berlin, Germany, knops.andre@gmail.com.
2
Center for Mind/Brain Sciences, University of Trento, I-38068 Rovereto, Italy, National Institute of Health and Medical Research, Unit 992, Cognitive Neuroimaging Unit, F-91191 Gif/Yvette, France, Atomic Energy and Alternative Energies Commission, Departement of Life Sciences (DSV)/Biomedical Imaging Institute (I2BM), NeuroSpin Center, F-91191 Gif/Yvette, France, and.
3
Center for Neural and Cognitive Sciences, University of Hyderabad, 500046 Hyderabad, India.
4
National Institute of Health and Medical Research, Unit 992, Cognitive Neuroimaging Unit, F-91191 Gif/Yvette, France, Atomic Energy and Alternative Energies Commission, Departement of Life Sciences (DSV)/Biomedical Imaging Institute (I2BM), NeuroSpin Center, F-91191 Gif/Yvette, France, and.
5
Center for Mind/Brain Sciences, University of Trento, I-38068 Rovereto, Italy.

Abstract

Human cognition is characterized by severe capacity limits: we can accurately track, enumerate, or hold in mind only a small number of items at a time. It remains debated whether capacity limitations across tasks are determined by a common system. Here we measure brain activation of adult subjects performing either a visual short-term memory (vSTM) task consisting of holding in mind precise information about the orientation and position of a variable number of items, or an enumeration task consisting of assessing the number of items in those sets. We show that task-specific capacity limits (three to four items in enumeration and two to three in vSTM) are neurally reflected in the activity of the posterior parietal cortex (PPC): an identical set of voxels in this region, commonly activated during the two tasks, changed its overall response profile reflecting task-specific capacity limitations. These results, replicated in a second experiment, were further supported by multivariate pattern analysis in which we could decode the number of items presented over a larger range during enumeration than during vSTM. Finally, we simulated our results with a computational model of PPC using a saliency map architecture in which the level of mutual inhibition between nodes gives rise to capacity limitations and reflects the task-dependent precision with which objects need to be encoded (high precision for vSTM, lower precision for enumeration). Together, our work supports the existence of a common, flexible system underlying capacity limits across tasks in PPC that may take the form of a saliency map.

PMID:
25057189
DOI:
10.1523/JNEUROSCI.2758-13.2014
[Indexed for MEDLINE]
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