Modeling dysfunction of the prefrontal executive system.
    The concept of executive function in the brain is given a new definition, as based in a distributed neural system whereby prefrontal cortex is interconnected with various other cortical and subcortical loci.  Executive function is divided roughly into three interacting parts: affective guidance of response; establishing linkage among working memory representations; and forming complex behavioral schemata.  Neural network models of these parts are reviewed and fit into a preliminary theoretical framework.