Conduction velocity of intracortical axons in monkey primary visual cortex grows with distance: implications for computation

A critical visual computation is to construct global scene properties from activities ofearly visual cortical neurons which have small receptive fields.Such a computation is enabled by contextual influences, through which a neuron’s responseto visual inputs is influenced by contextual inputs outside its classical receptive fields.Accordingly, neurons can signal global properties including visual saliencies andfigure-ground relationships. Many believe that intracortical axons conduct signalstoo slowly to bring the contextual information from receptive fields of other neurons.A popular opinion is that much of the contextual influences arise from feedbackfrom higher visual areas whose neurons have larger receptive fields.This paper re-examines pre-existing data to reveal these unexpected findings:the conduction speed of V1 intracortical axons increases approximately linearlywith the conduction distance, and is sufficiently high for conveying the contextualinfluences. Recognizing the importance of intracortical contribution tocritical visual computations should enable fresh progress in answering long-standing questions.