Orientation tuning and synchronization in the hypercolumn model.

The orientation selectivity in the firing rate of neurons is one of the most well-known properties of neurons in the primary visual cortex. To understand the dynamical mechanism of the orientation tuning, we introduce a biologically plausible network for a hypercolumn and investigate dynamical responses of its columnar activities. Numerical simulations show that the spike activities between excitatory cells in the same column exhibit strong synchronization and sharp orientation selectivity. The tuning curves for the synchronized activities also show orientation selectivity similar to those for the firing rate. The comparison between the two tuning curves for the firing rate and the synchronized activities suggests that the orientation selectivity is strongly correlated with the synchronized activities. We find from the analysis of columnar activities that the orientation selectivity depends strongly upon the inhibitory coupling strength and the synchronization upon the excitatory coupling strength. In particular, we find that at appropriate coupling parameters both sharp orientation selectivity and maximal synchronization can be achieved. This suggests the importance of the balance between the excitatory coupling and the inhibitory coupling in the primary visual cortex for visual information processing.