Lateral Excitation between Dissimilar Orientation Columns for Ongoing Subthreshold Membrane Oscillations in Primary Visual Cortex

Abstract

Primary visual cortex (V1) is the first stage of visual information processing; detection of particularly oriented bars. These elemental visual features are sent to higher visual regions including V2, in which their combinations such as ”corners” and ”junctions” are processed. A recent study has demonstrated that corners and T-junctions could be processed even at the early visual stage (V1), raising the question of why the binding of bars by V1 is necessary. We simulated a V1 neural network model, in which the so-called ”orientation-columns” were connected through both excitatory and inhibitory synapses. The lateral excitatory connections contributed not only to binding paired bars constituting corners but also to making membrane oscillations near firing-threshold during ongoing (spontaneous) neuronal activity periods. This ongoing subthreshold neuronal state led to accelerating the reaction speed of neurons to paired bar-stimuli. The lateral inhibitory connections effectively enhanced the selective responsiveness of neurons to the stimuli. We suggest that coordinated lateral excitation and inhibition between orientation-columns in V1 could send angular information such as corners and junctions, presented to retina, rapidly to the next stage V2 for its full and precise analyses.