Fig. 4.

The structural model links laminar patterns of connections to the cortical type difference between linked areas. A–C: sequence of predicted patterns of connections that link areas with lower (left) to areas with higher (right) laminar elaboration. These connections have been called “feedback.” D–F: sequence of predicted patterns of connections that link areas with higher (right) to areas with lower (left) laminar elaboration. These connections are called “feedforward.” The diagram is oversimplified and does not depict all possible combinations of connections, such as those between areas with the lowest and highest laminar structure, which are in the minority among actual connections. The diagram also does not depict connections between areas of similar type, which have been called “lateral” and are ubiquitous in the cortex, or other combinations between areas of different type. Roman numerals indicate cortical layers.