Cortical columns and the tendency of neighboring neurons to act similarly

A tendency by neighboring cortical neurons to act similarly (spatial assimilation) is derived analytically from an assumed facilitatory interaction between the involved neurons at an early age, possibly before the critical period in the cat, an assumed plastic modifiability of the thalamo-cortical contacts at the same earlier time, and exposure of the network at the same time to a largely arbitrary sequence of inputs coming from outside the cortex. The calculational result is that during the assumed period of thalamo-cortical plasticity neuron responses tend toward greater similarity within the approximate range where cortico-cortical excitation dominates over inhibition and toward greater dissimilarity where inhibition dominates over excitation. Through the result, the calculation correctly predicts the horizontal extent of certain cortical columns. In the visual cortex of certain animals the horizontal distance of most dissimilar preferred orientation (90 degrees difference) is about the same as the distance of most dissimilar eye preference (from center of left-eye to center of right-eye region), and both are roughly the same as the range of strongest intracortical inhibition. The sequence of inputs coming from outside the cortex is mathematically allowed to be random, which suggests that signals originating inside the nervous system, as exist in a sensorially deprived animal, without help from genetic specifications, are adequate to give rise to spatial assimilation.