Correlating Excitation and Inhibition in Visual Cortical Circuits: Functional Consequences and Biological Feasibility
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- Jens Kremkow. Correlating Excitation and Inhibition in Visual Cortical Circuits: Functional Consequences and Biological Feasibility, URL . 2009 abstractThe primary visual cortex (V1) is one of the most studied cortical area in the brain. Together with the retina and the lateral geniculate nucleus (LGN) it forms the early visual system. Artificial stimuli (i.e. drifting gratings (DG)) have given insights into the neural basis of visual processing. However, recently researchers have started to use more complex natural visual stimuli (NI), arguing that the low dimensional artificial stimuli are not sufficient for a complete understanding of the visual system.For example, whereas the responses of V1 neurons to DG are dense but with variable spike timings, the neurons respond with only few but precise spikes to NI. Furthermore, linear receptive field models provide a good fit to responses during simple stimuli, however, they often fail during NI. To investigate the mechanisms behind the stimulus dependent responses of cortical neurons we have built a biophysical model of the early visual system.Our results show that during NI the LGN afferents show epochs of correlated activity, resulting in precise spike timings in V1. The sparseness of the responses to NI can be explained by correlated inhibitory conductance. We continue by investigating the origin of stimulus dependent nonlinear responses, by comparing models of different complexity. Our results suggest that adaptive processes shape the responses, depending on the temporal properties of the stimuli. Lastly we study the functional consequences of correlated excitatory and inhibitory condutances in more details in generic models.The presented work gives new perspectives on the processing of the early visual system, in particular on the importance of correlated conductances..
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This work was supported by European integrated project FP6-015879, "FACETS".