Executive functioning

The frontal lobes, which make up 40% of the human cerebral cortex, are greatly expanded in humans compared to non-human primates (Stuss & Benson, 1986). Far from a monolithic structure with a single purpose, the frontal lobes are divided into multiple structurally, physiologically and functionally distinct regions with important functions related to movement, motor planning, language, intelligence, working memory, generation, inhibition, alternating sequences, drive, emotion, self-awareness, insight, and personality.

The cognitive functions most commonly attributed to the frontal lobes are higher order or executive processes which involve the organization of more basic cerebral processes to promote efficient task performance and establishment of associations beyond basic representation of incoming sensory information. Examples of important cognitive functions of the frontal lobes include abstraction, inhibition, and facilitating the shifting of cognitive sets (Fuster, 1997; Luria, 1966). Also, the frontal lobes play a key role in attention, memory (particularly working memory) and language.

Efficient, successful completion of tasks requires the ability to avoid distraction and to maintain mental effort on a given task until it is complete. Patients with frontal lobe damage are often impaired in these functions, leading them to be distractible, disorganized and very inefficient (Zakzanis, 1998).

Often we are required to maintain two or more tasks in mind simultaneously, and constantly shift between them. In addition, it is sometimes necessary to suppress the impulse to perform certain tasks to reach our goals. These functions are significantly impaired with frontal lobe injury (Luria, 1966) with profound consequences.

Many of the functions described above are associated with the dorsolateral portions of the frontal lobes. Generally, verbal tasks disproportionately tap left frontal functions, while visual tasks are more likely to use the right frontal lobe. Inhibition tasks seem to rely upon both the dorsolateral and the orbital frontal region. A variety of disorders with selective subcortical involvement, like progressive supranuclear palsy, disconnect the frontal lobes from subcortical activation and lead to frontal lobe neuropsychological syndromes.