Event Abstract Back to Event Novel self-organizing rules for retinotopic remapping Markus Butz1* and Arjen Van Ooyen2 1 Ruhr-University Bochum, Institute for Neural Computation, Germany 2 VU Amsterdam, CNCR, Netherlands Retinotopic maps in the primary visual cortex are plastic even in the mature brain. Particularly after permanent changes in external input, i.e. after focal retinal lesions, maps in the cortex adapt so that neurons deprived of input (lesion projection zone, LPZ) become responsive to adjacent input representations. This 'filling-in' process is currently explained by STDP. However, STDP is a fast process while the time course of reorganization continues over weeks until one year [1]. Recent data indicates that structural plasticity (forming new synapses, breaking old ones) is involved in this reorganization [2,3] and acts very much on the same time scale. Therefore, we propose the first model investigating structural plasticity in application to cortical remapping. The model implements local activity-dependent rules for changes in the morphology of the neuron. In accordance with experimental findings, model neurons aim to maintain their electrical activity on average at a certain pre-defined set-point [4] by adapting the number of contact sites (axonal and dendritic elements). New (vacant) synaptic elements are offered to the network and connect to form synapses. The probability for synapse formation between two neurons depends on the amounts of vacant synaptic elements offered and the Euclidean distance between the two neurons. Network rewiring is therefore a reciprocal process between activity and network structure: Activity levels inside the LPZ (low) and outside the LPZ (high) locally induce the formation of axonal and dendritic elements, respectively, that in turn form synapses in a cooperative and compensatory manner leading to increasing activities in the LPZ again. The consequence of transporting activities via new synapses from the outside of the LPZ into the LPZ is an enlargement of input representation from intact areas and a sequential filling-in of the LPZ (Fig. 1)—by contrast not obtained in self-organizing maps. The novelty of the model is to generate predictions how local cellular responses lead to rewiring and remapping on an anatomical network level. Caption Figure 1: Cortical remapping emerges from new horizontal connections formed from intact areas into the LPZ. A) Colors indicate spatial input representations. White dashed circle indicates LPZ. B) New connections impinging on cells in the LPZ (white dots). Connections originating in the peri-LPZ (green), LPZ border (orange), LPZ center (blue). Horizontal and vertical bars indicate the relative position of the areas to the entire network. Figure 1 Acknowledgements MB was supported by a grant (635.100.017), awarded to AvO, of the Computational Life Sciences program of the Netherlands Organization for Scientific Research.
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