The cerebral cortex is pivotal in information processing and higher brain function and its laminar structure of six distinct layers, each in receipt of a different constellation of inputs, makes it important to identify connectivity patterns and distinctions between excitatory and inhibitory pathways. The 'feedforward' projections from layer 4-3 and from 3-5 target pyramidal cells and to lesser degrees interneurones. 'Feedback' projections from layer 5-3 and from 3-4, on the other hand, mainly target interneurones. Understanding the microcircuitry may give some insight into the computation and information processing performed in this brain region.