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In a recent model-based analysis of intracellular single unit recordings from cat visual cortex [1] we have found strong evidence, that the visual cortical network operates in a regime where the local cortical network provides dominant excitatory and inhibitory recurrent inputs (compared to the feedforward drive). Most interestingly, the data supports an operating regime which is close to the border to instability, where cortical responses are sensitive to small changes in neuronal properties, for example changes induced through neural adaptation. Here I would like to extend our model-based analysis to experimental data on orientation adaptation [2,3], i.e. on the stimulus induced changes of orientation tuning curves in cat primary visual cortex. Using a systematic exploration of model space we evaluate the hypothesis, that fast synaptic adaptation is responsible for orientation adaptation. Indeed we find a large number of admissible models (1,000 from 50,000 combinations of adaptation parameters for models in the abovementioned balanced recurrent regime), i.e. models whose predictions are consistent with the data. These models form a connected "island" in parameter space indicating one underlying mechanisms. Observed differences between pinwheel and domain regions can also be explained within this model framework. Finally, we observe that different sets of synaptic parameters lead to changes of orientation tuning curves different from cat V1 but similar to what has been found in area MT of macaques [4]. Different experimental findings may - therefore - still be explained by the same biophysical mechanism. [1] Stimberg et al. (2009), The Operating Regime of Local Computations in Primary Visual Cortex, Cerebral Cortex 19, 2166-2180. [2] Jin et al. (2005), Tilt Aftereffect and Adaptation-induced Changes in Orientation Tuning in Visual Cortex, J. Neurophys. 94, 4038-4050. [3] Dragoi et al. (2001), Foci of Orientation Plasticity in visual Cortex, Nature 411, 80-86. [4] Kohn & Movshon (2003), Neuronal Adaptation to Visual Motion in Area MT of the Macaque, Neuron 39, 681-691. |
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