Executive dysfunction

From Psy3241

Current revision as of 02:43, 29 April 2008

Executive Functioning

Lezak (1995) defines executive functions as the ability to engage in independent, purposeful, and goal-directed behaviors. Many of the abilities associated with executive functioning include: attention, planning, initiation, self-monitoring, organization, response inhibition, and generative behavior (Lezak, 1995). Higher order processing such as this allows us to use internal and external feedback in order to adjust behavior to better respond to environmental demands. Executive abilities are most used in novel or complex situations in which previous learning and recall of information are minimized. Executive functions are activated by tasks that require forming new concepts, visual memory tasks, and tasks related to nonverbal abilities. Executive functioning, rather than relating directly to a specific cortical region (such as the frontal lobes) is better described as those attributes that are supervisory, controlling, and organizational (Sterling, 2000).

Executive Impairments

Moderate and severe executive dysfunction may result from a myriad of medical problems: cerebrovascular disease, neurodegenerative disease, epilepsy, psychiatric disorders and toxic-metabolic-infectious conditions (Busch et al., 2005). Executive dysfunction resulting from damage to dorsolateral prefrontal cortex includes impaired planning, flexibility in responding, and working memory. Contrastingly, executive dysfunction resulting from damage to dorsomedial frontal cortex includes impaired initiation, sequencing, and sustained effort (Lezak, 1995). Additionally, frontal lobe syndrome, resulting in executive dysfunction, frequently occurs after damage to subcortical structures. Memory impairments in ED are seen in working memory, temporal memory and source memory. Specifically, frontal lobe dysfunction may result in an episodic memory deficit that is related to the context in which the task, event, or stimulus was learned.

Neuropsychological Tests

Sterling (2000) describes which psychological assessments are used to determine impairments in each domain of executive dysfunction:

• Impairments in action control are assessed via the memory for designs test. Those with this disorder will display perseverative responding, in which each drawing looks similar to the one drawn immediately before it (Sterling, 2000).

• Impairments in abstract and conceptual thinking are assessed via the Wisconsin card sort test (WCST). Those patients with ED will exhibit slowed learning to sort and perseverative errors, indicating they have lost flexibility in behavioral responding necessary to adapt to the new rules of the game (Sterling, 2000).

• Impairments in goal-oriented behavior include impairments in sequential planning and self-monitoring. Sequential planning deficits can be assessed via the Tower of London test, in which the behavior should seem aimless, lacking strategy. When deciphering impairments in self-monitoring, the clinician can delegate daily tasks such as keeping an appointment or shopping for a specific item, in order to assess the success of achieving the goals of the task. Patients with ED will display distractions and a general lack of awareness in not attaining the goals (Sterling, 2002).

• Inhibition and attention deficits can be assessed via the Hayling test.

Cases and Research

The famous case of Phineas Gage, who suffered from frontal lobe damage, displayed the way in which ED can manifest not in intellectual deficits, but in a lack of behavioral inhibition, loss of social functioning, and change in personality (Sterling, 2000).

Biederman et al. (2008) studied executive functioning deficits in girls with attention-deficit-hyperactivity disorder (ADHD) over a five-year period. Interestingly, subjects with ADHD showed stability in executive functioning impairments in working memory, interference control, visuospatial organization, processing speed, and verbal learning compared to controls (Biederman et al., 2008).

Bull, Phillips and Conway (2008) used dual-task manipulations of executive functions to explore their role in mental state and non-mental state tasks. Specifically, the investigators assessed subjects’ ability to inhibit, update and switch using the “Eyes” and “Stories” theory of mind tasks. The authors found that theory of mind, or the ability to comprehend other's cognitions and intentions, is crucial for social functioning and requires intact executive functioning.

References

Bull, R., Phillips, L. H., & Conway, C. A. (2008). The role of control functions in mentalizing: Dual-task studies of theory of mind and executive function. Cognition, 107, 663-672.

Busch, R. M., Booth, J. E., McBride, A., Vanderploeg, R. D., & Curtiss, G. (2005). Role of executive functioning in verbal and visual memory. Neuropsychology, 19(2), 171-180.

Biederman, J., Petty, C. R., Doyle, A. E., Spencer, T., Henderson, C. S., Marion, B., Fried, R., & Faraone, S. V. (2008). Stability of executive function deficits in girls with ADHD: A prospective longitudinal followup study into adolescence. Developmental Neuropsychology, 33(1), 44-61.