Cortical organization of voluntary behavior in man

The research on regional changes in metabolism and blood flow in the human cerebral cortex during physiological activations is reviewed, with special reference to the significance of these changes for the organization of voluntary behavior. The only difference between cortical metabolic increases associated with voluntary behavior and cortical metabolic increases not associated with voluntary behavior was the activation of the primary motor cortex. Prior to the execution of any specific brain work, the brain tuned and prepared the cortical fields that were expected to participate in the task. This was reflected in metabolic increases in multiple cortical fields of a few cm2 which were then recruited for the task. Execution of the task increased the metabolism in those same cortical fields. The activated cortical fields constituted the largest functional elements of the cortex. If voluntary behavior was required, fields in the motor areas were recruited; otherwise, the organization of voluntary behavior did not differ from other brain work. In contrast to other cortical areas studied, the activation of the superior prefrontal cortex was independent on task-specific algorithms, sensory input and motor output. Its anterior division was always activated in tasks that were carried out according to a prior instruction; the mid-division was activated when the brain fixed attention or switched it between different cortical fields; the posterior division was activated when the paradigm contained sequential contingencies. The three sections of the superior prefrontal cortex participated in the organization of brain work by participating in the recruitment and attention control of cortical fields.