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Adaptation-induced changes in orientation tuning and tilt aftereffect in network models of V1
Zitatschlüssel Wimmer2009
Autor Wimmer, K. and Obermayer, K.
Buchtitel Computational and Systems Neuroscience
Jahr 2009
Zusammenfassung The perception of a sensory stimulus depends on its temporal context. A well studied psychophysical phenomenon is the tilt aftereffect in which an adapting context stimulus causes a vertically orientated test stimulus to appear repulsed away from the context orientation. Physiological studies have identified the accompanying changes in orientation tuning of individual neurons in primary visual cortex: (1) tuning curves shift repulsively away from the adapting stimulus, (2) responses close to the adapting stimulus are suppressed. Previous modeling studies have been purely conceptional or have focused either exclusively on the perceptual (tilt aftereffect) or the physiological (tuning curve changes) effects. Here, we investigate whether synaptic depression in firing rate models can produce behavior compatible with both perceptual and physiological findings. We first parameterize simple ring models, so that model cells receive strong recurrent excitation and inhibition, both dominating the feed-forward input. We have shown previously [1] that only such an operating regime is compatible with experimental data on orientation tuning in primary visual cortex. In this ring model, we then systematically vary the strength of the synaptic depression parameters for the four types of recurrent connections (excitatory -> excitatory, excitatory -> inhibitory, inhibitory -> inhibitory, and inhibitory -> excitatory). Each parameterization gives rise to a different model instance, which is then used to simulate adaptation experiments: first orientation tuning curves of model cells are measured in the unadapted condition (control), then the model is adapted to a certain orientation, and tuning curves are measured again (test). We find that, depending on the relative strength of the depression parameters, tuning curves of individual cells as well as the population responses can either show attractive or repulsive shifts, and adaption can lead to both, response suppression or facilitation. The adaptation-induced changes in tuning curves and population responses are then compared to experimental data. The data provides strong evidence for those network models where inhibitory synapses depress less than excitatory synapses, and excitatory to excitatory connections have strongest depression. Only a relatively small range of the model space gives rise to adaptation-induced changes that are compatible with the experimental data. We use these results to construct two-dimensional fire rate models that incorporate a biologically plausible topographic orientation preference map. With these models, we can investigate how the tuning curve shifts of model neurons depend on the local intercortical interactions. It has been found experimentally, that adaptation induced changes are more pronounced close to pinwheel centers. Indeed, in the model adaptation has a stronger effect on the broadly tuned recurrent inputs near pinwheels, which in turn also leads to larger tuning curve shifts. We do not observe this difference between pinwheel and orientation domain cells in models with weak recurrent interactions. Thus, the pronounced adaptation near pinwheel centers is a consequence of the enhanced sensitivity to modulations of connection strengths in the strong recurrent network regime.
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