A Neural Network Model of Intraparietal Sulcus That Can Explain a Pattern of Brain Imaging Results Related to the Visual Working Memory
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University of Rijeka, Department of Psychology, Netherlands
Aim: The purpose of this work is to develop and test a neural network model of the intraparietal sulcus (IPS) and to delineate computational mechanisms that can implement "neural" object file theory (1).
Methods: The Proposed neural network is based on the previous model of figure-ground organization where feature binding is achieved using firing rate (2). All nodes that participate in the representation of the same object are labelled with the same activity amplitude. On the other hand, nodes representing different objects are kept segregated due to the lateral inhibition among them. Lateral inhibition is modulated by the dendritic inhibition which selectively prevents inhibition among node encoding the same object. Central component of the model are dendrites which operate as independent computational units. The model is extended to incorporate feature stores (i.e. shape, colour) in the superior IPS and separate store for object's location in inferior IPS. The interpretation of the fMRI findings is based on the assumption that local field potential is a major component of the BOLD signal and that processing at dendritic trees are major component of the local field potential.
Results: Computer simulations showed that the proposed model exhibits capacity limit to about four objects that could be simultaneously stored in the working memory. A model of inferior IPS showed linear increase in activation up to the four objects irrespective of their shape or other properties. On the other hand, model's superior IPS showed variable capacity limit which depends on the complexity of objects. Complex objects required more active nodes to encode and represent their features. This resulted in stronger lateral inhibition among competing representations and consequently in weaker brain activation and in lower capacity estimate for complex objects.
Conclusion: The presented model is able to account for a different pattern of neural activation in the inferior and superior parts of the IPS as revealed by the fMRI data obtained while participants were engaged in solving change detection task. The model emphasised the role of dendrites as crucial component contributing to the generation of BOLD signal.
Acknowledgments: Funded by the Croatian National Foundation for Science, Higher Education and Technological Development (02.05/06), Croatian Ministry of Science, Education and Sport (009-0362214-0818) and the Bial Foundation (80/06).
References
1. Selecting and perceiving multiple visual objects. Xu Y, Chun MM, Trends in Cognitive Sciences 13 (2009) 167–174.
2. A feedback model of figure-ground organization. Journal of Vision 8 (2008) 1-27.
Conference:
NeuroMath COST Action BM0601: Neurodynamic Insight into Functional Connectivity, Cognition, and Consciousness, Dubrovnik, Croatia, 27 Mar - 28 Mar, 2010.
Presentation Type:
Oral Presentation
Topic:
Talks
Citation:
Domijan
D
(2010). A Neural Network Model of Intraparietal Sulcus That Can Explain a Pattern of Brain Imaging Results Related to the Visual Working Memory.
Front. Neurosci.
Conference Abstract:
NeuroMath COST Action BM0601: Neurodynamic Insight into Functional Connectivity, Cognition, and Consciousness.
doi: 10.3389/conf.fnins.2010.05.00013
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Received:
24 Jul 2010;
Published Online:
24 Jul 2010.
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Correspondence:
Drazen Domijan, University of Rijeka, Department of Psychology, Rijeka, Netherlands, ddomijan@ffri.hr