This project is concerned with an analysis of the activity of nerve cells in that system within the primate brain which is necessary and responsible for the process we refer to as attention. Monkeys trained to perform visually-guided go, no-go discrimination tasks are tested whilst extra cellular recordings are made from brain regions thought to be part of an attentional system. The most recent study in this series examined structures in the forebrain. The exploration of the frontal cortex now has been completed. We found attention related units in the prefrontal cortex including the prearcuate, the periprincipalis and anterior cingulate areas. These cells responded to the manipulation of attention, e.g., manipulation of the pre-stimulus waiting period or changing the behavioral significance of the task-stimuli. These attention-related units have properties similar to those found in the brainstem reticular formation in previous studies.