Recurrent cortico-cortical Interactions in neural disease

The cerebral cortex consists of a large number of areas, each subserving a more or less distinct function. This view has its roots in the early work of Penfield, and today is reflected in the body of functional MRI literature describing the regions of the brain that are activated during particular tasks, percepts, actions or thoughts. Moreover, the currently held view is that these areas, and their associated functions, are organized in a hierarchical fashion: some areas are low level, performing basic operations on the sensory input. Via feedforward cortico-cortical connections, this information is transferred to intermediate and high level areas, where more sophisticated processes occur, like object recognition, multi-sensory integration, decision making, attention, or reasoning. This view is now being challenged. Feedforward connections are reciprocated by numerous feedback fibers. Within areas, there are extensive horizontal connections that link neurons separated by large distances. Together, horizontal and feedback connections provide the anatomical basis for extensive recurrent processing, where low and high level information interacts. However, only recently we have gained some insight in how recurrent interactions work, and what their function might be. They provide cognitive operations, ranging from perceptual organization to awareness and attention. These insights have implications for understanding neurological and neuropsychological disease.