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Analysis of Neural Data

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The local recurrent network influences surround modulation in a model of V1
Citation key stim09
Author M. Stimberg and K. Obermayer
Title of Book Society for Neuroscience Abstracts
Pages Program No. 850.9
Year 2009
Abstract The response of a cell in primary visual cortex does not only depend on the stimulus presented in the classical receptive field, but also on the spatial context. The strength and sign of the modulation from the surround depends on the properties of both the center and the surround stimulus, most notably their contrast and orientation. Likely anatomical substrates for such center-surround interactions are the lateral long-range connections and the feedback connections from higher visual areas. However, it is also known that the local recurrent network within a single hypercolumn strongly shapes the response of a neuron. In a recent modeling study [1] of a two-dimensional network with an artificial orientation map layout, it was shown that only a parameter regime with strong recurrent connections is compatible with physiological data on orientation tuning. Here, we extend this study by determining the influence of the local network on modulatory surround effects. The model includes an additional, orientation-tuned surround input as an effective description of the surround influence. We explore this model class by independently varying the center contrast, the strength of the local connections between and within excitatory and inhibitory neuronal populations, and the surround input to the two populations. Within this model class, various forms of suppression and facilitation can be achieved. In particular, models with surround input to both excitatory and inhibitory cells are capable of showing facilitation at low and suppression at high center contrast as observed in experiments. We furthermore find that for strong local inhibitory connections, the surround effect does not have to be the same for cells at different map positions; even though the surround input itself does not depend on map position, it is also mediated by the local neighbourhood and therefore influences cells' responses in a different way, according to their map position. We make a similar observation when measuring the tuning of the surround influence: In a subclass of models, the surround influence is more broadly tuned in cells close to singularities of the orientation map. These findings demonstrate the importance of taking the map structure into account when analyzing modulatory effects from the surround. [1] M Stimberg, K Wimmer, et al. The Operating Regime of Local Computations in Primary Visual Cortex. Cereb Cortex, Epub ahead of print (2009).
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