Wednesday, January 17, 2018

Reading :: Executive Functions and the Frontal Lobes

Executive Functions and the Frontal Lobes: A Lifespan Perspective
Edited by Peter J. Anderson,‎ Vicki Anderson,‎ and Rani Jacobs

In this collection, the authors discuss the fascinating subject of executive functions, something that I have lightly covered on this blog in my recent reviews of books on aphasia. This collection, however, covers the entire lifespan: childhood to old age, healthy development to recoveries from injuries.

"Executive function," Peter J. Anderson explains in Chapter 1 ("Towards a developmental model of executive function"), "is not a unitary cognitive process, but instead is a psychological construct that is composed of multiple interrelated high-level cognitive skills" (p.3). It is
a collection of interrelated functions, or processes, which are responsible for goal-directed or future-oriented behavior, and have been referred to as the 'conductor' which controls, organizes, and directs cognitive activity, emotional responses and behavior (Gioia, Isquith, & Guy, 2001). The key elements of executive function include (a) anticipation and deployment of attention; (b) impulse control and self-regulation; (c) initiation of activity; (d) working memory; (e) mental flexibility and utilization of feedback; (f) planning ability and organization; and (g) selection of efficient problem-solving strategies. (p.4)
Anderson overviews several models of executive function, including the supervisory attentional system (SAS) model (pp.7-9), the working memory model (pp.9-11), the model of executive (self-regulatory) functions (pp.11-13), components of executive functions (pp.13-14), problem-solving framework (pp.14-15), and executive control system (pp.15-18).  He identifies strengths and weaknesses of each. (Note: In Chapter 17, "Models for the rehabilitation of executive impairments," authors Barbara A. Wilson and Jonathan Evans state that the SAS model is closely related to Luria's conception of problem-solving; p.389).

In Chapter 2, Cinzia R. De Luca and Richard J. Leventer discuss "Developmental trajectories of executive functions across the lifespan." They begin by explaining that EF are not just localized to the frontal lobes (and call out Luria 1973 for treating the two as synonymous) (p.24). But the frontal lobes do play a large role in EFs, and the frontal lobes degenerate first—both in aging and in pathological dementias (p.25).

The authors break down development into several stages and provide detailed tables for each stage, allowing us to see how brain development and EF relate by year. For instance, we find that at age 4, children increase both gray and white matter volumes as well as metabolism; they see improved cognitive flexibility at this age (p.34). Between ages 9-12, most EFs demonstrate a spurt, including working memory, strategic thinking, fluency, and goal-directed behavior (p.35). Through adolescence, white matter increases and gray matter volume decreases (p.36). From the mid-20s until the late 30s, "the major change in the PFC [prefrontal cortex] is the continued steady increase in myelination" or the fatty insulation around axions (p.39). Peak EF skills are realized from 20-29. Alas, "brain weight begins to decline from age 30, dropping by 10% to age 90," correlating with a long slow decline in EF skills (p.40).

But there is hope for us above 30. Although older people perform more poorly on clinical planning tasks, they perform as well as a younger cohort on ecologically valid planning tasks (p.41). The discrepancy reflects "the greater opportunity to effectively apply compensatory strategies and knowledge to successfully perform everyday task types" (p.41)—in other words, older people have learned mediatory strategies or picked up mediatory tools to which they can shift some of the cognitive burden.

In Chapter 3, Louise H. Phillips and Julie D. Henry discuss "Adult aging and executive functioning" in more detail. They note that since each EF "involves a complex network of brain areas and multiple cognitive processes," aging does not affect all in the same way (p.58). Interestingly, older adults see more prefrontal activation, and more bilateralized activation, than younger adults when performing the same cognitive tasks—likely because prefrontal decline requires more neural recruitment to compensate (pp.58-59).

The authors examine the evidence of how aging affects various EFs. Interestingly, in older people, planning is slower and involves more moves, but goal conflict handling—which is involved in the most difficult planning tasks—does not appear to decline (pp.68-69). The authors conclude by calling for more research on "well-practiced or socially relevant executive tasks" (p.73).

In Chapter 8, "Assessment of behavioral aspects of executive function," authors Gerald A. Gioia, Peter K. Isquith, and Laura E. Kenealy begin by discussing ecological validity and the assessment of EF. They define ecological validity as "predictive value of functioning in the everyday environment" (p.179) and contrast it with traditional (construct) validity (p.181). Ecological validity has obvious ramifications for "implications and predictions for the individual in his or her everyday milieu" (p.181). The authors overview various assessment methods to get at ecological validity.

In Chapter 18, Mark Ylvisaker and Timothy Feeney's "Helping children without making them helpless: Facilitating development of executive self-regulation in children and adolescents," the authors specifically examine self-regulation in children. Children often have "weak self-regulation" if they have "neurological impairment or immaturity" such as ADHD; "chaotic, unpredictable, disorganized home environments"; "weak emotional attachments" to adults, such as children in the foster care system; "few opportunities for legitimate control over events in their lives"; and developmental immaturity (p.413). The authors embrace a Vygotskian approach and use "a typical developmental template for developing intervention and support strategies" (p.414). One typically Vygotskian approach they use is to provide a script that children can internalize "as automatic SR [self-regulation] self-talk" (p.416). The authors provide several cases to illustrate this approach. They also describe teaching compensatory strategies (p.425). They conclude by advocating the approach of identifying strengths and goals as opposed to "pathology-oriented interventions that focus primarily on identifying deficits for purposes of their amelioration" (p.432).

Overall, the book was fascinating to me. After reading the foundational works of Vygotsky and Luria, I have been thinking about how a Vygotskian approach to workplace/professional writing might involve better understanding the EFs that collectively support writing and information tasks. Reading this collection, in addition to similar work on aphasia, gave me a much better idea of what has been built on that Vygotsky-Luria foundation, as well as how complicated our cognition really is. If you're similarly interested in these themes, I recommend this book.