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The first offers a conceptualization of executive functions (EF) intended to remedy flaws in prevailing ideas about them, which Barkley identifies in a withering critique. The central idea he elaborates is that EF are “self-directed actions needed to choose goals and to create, enact, and sustain actions toward those goals” (p. 60). Notice the verbs in this definition – for example, choose, create – because they signify Barkley's real passion, reclaiming, on behalf of the living, socially engaged, striving self, territory in psychology now occupied by pallid, eviscerated entities such as the “central executive.” Barkley's criticism of the EF field dutifully includes concerns about the psychometric properties of current measures, the tendency to confuse anatomical localization with a meaningful definition (e.g., EFs are “what the frontal lobes do”), and weak consensus on core concepts. But he saves his most vehement language to attack the reductionism of the individual to, in essence, software: “Instead, cognitive neuropsychology's view of humanity is frankly not worth having – an Orwellian automaton of an information processor without a sense of self.”
Barkley goes on to enumerate eight fundamental capacities upon which EF, as he defines them, develop. Spatial, temporal, motivational, inhibitory, conceptual/abstract, behavioral-structural, social, and cultural capacities all get their moments in the spotlight. Although not exactly pulled out of thin air, the framework is chiefly heuristic and derived, unapologetically, more from reason than evidence of how the brain might actually work. However, Barkley offers at least one intriguing, and, I think, elegantly argued, idea: That beneath it all lie the capacities for vicarious learning and contemplation to anticipate and manage situations that one has not personally encountered, which are, perhaps, the game changers in human evolution. But all this is a prelude to the next Great List that occupies nearly half the book, a hierarchy of human functions and activities that EF enable, and an analysis of how their effects on the social and physical environments boomerang back to shaping the individual's behavioral repertoire.
These ripple effects of human activities that EF enable give rise to the second theme, which could easily have spawned a separate book. Barkley argues that these extended effects are the “why” of EF. To explain the evolution of EF, Barkley turns to the extended phenotype concept developed by Dawkins (Dawkins 1999). The kernel of the extended phenotype idea is that the effects of a genotype extend beyond the organism that houses it. When such distal effects of a particular allele help to propagate it in succeeding generations (i.e., natural selection favors it), these effects are as much part of the gene's phenotype as, for example, hair color. Dawkins realizes that at first glance this is an unusual way to think about gene effects, and eases us into the idea by pointing out that the proximal effect of any coding gene is simply to synthesize a protein. How that protein, in tandem with other parts of the genome, gives rise to any characteristic of the organism, is already an enormous way down the road from that initial biochemical consequence. We could readily accept that web construction is a rather direct consequence of a spider's genome. Any number of allelic variants might arise that improve the web's food-catching capability or that require less energy to create it, and would be favored by natural selection. Why not regard the web itself, or any other artifact that an organism creates, as part of the gene's phenotypic expression? Or, as Dawkins puts it, “In a very real sense, her web is a temporary functional extension of her body, a huge extension of the effective catchment area of her predatory organs” (Dawkins 1999, p. 198). Another oft-cited example that profoundly changes ecology for numerous animals is the beaver dam that “creates a large shoreline which is safe and available for foraging without the beaver having to make long and difficult journeys overland” (Dawkins 1999, p. 200). The genes responsible for this behavior can claim not only the dam, but also the entire beaver lake as part of their extended phenotype. In addition to impacts on the environment that are favorable for propagating the responsible genes, impacts on other organisms are part of the extended phenotype also. Barkley leverages this insight to argue that the capacity for strategic interpersonal behavior is among EFs' most decisive influences on humanity.
This thought-provoking analysis is itself worth the price of the book, and for many readers, it will be an important introduction to developments in evolutionary biology beyond the basics. However, calling EFs themselves, rather than their effects, “extended phenotypes,” is not easily reconciled with Dawkins' ideas. Barkley skips over the “unit of evolution” issue that underlies Dawkins' work: It is not the individual organism whose “fitness” determines which traits are selected, but the genes themselves. The “interests” of the gene do not always coincide with that of the organism; it is in that sense that the gene is selfish. Barkley implies that EFs developed because their distal effects favored the fecundity of the animal that performed them, and it is that animal's self-interest that propels the whole enterprise. The model that Dawkins prefers, of complementarity of genes in a population, leads to a rather different explanation for a number of phenomena such as empathy, cooperative behavior, or leadership versus followership.
Barkley's discussion of evolutionary processes to explore “why EF?” exposes him to accusations of what, for many in evolutionary biology, is a mortal sin: Claiming that a trait arose in order to solve a specific problem, for a purpose, or, really, for anything bearing on “why.” In short, that sort of teleological thinking can be a source of fun speculation, but the hard-nosed underlying reality is that all genetically transmitted traits, including the forerunners of human EF, just happened to pop up as a random mishap of genetic shuffling, and proliferated in the population because they happened to improve reproductive success over the alternative alleles in that space in the genome. Maybe this apparent purposelessness is just as stale and “Orwellian” as the information-processing automaton notions of EF that Barkley detests, but this is the playground on which he chose to play ball.
The final chapter brings us back to more mundane concerns: The evaluation and treatment of EF deficits. Barkley suggests that existing tests of working memory, inhibition, and planning may be useful in assessment of some of the more basic functions at a fairly circumscribed level (the “Instrumental – Self-Directed Level”). Barkley's more expansive view of EF puts a higher premium on human functioning in context, which brings in the higher levels of methods and tactics. He favors direct observation and rating scale development. The remedial and compensatory approaches mentioned are not path breaking – many are found in current occupational therapy textbooks (e.g., Crepeau et al. 2003) – but linking them to the EF extended phenotype framework is an interesting way to organize them.
The book takes the reader on a rigorous intellectual journey through neuropsychology, evolutionary biology, and even a fair amount of political philosophy. It would be smoother sledding if there were more examples and hypotheticals to make the concepts more vivid, rather than the abstract presentations that dominate. The author might take a tip from Dawkins' own playbook, which shows that a technically demanding scientific exposition can be a best-seller when the author adds lots of anecdotes about nature, and “what if” scenarios. All the same, this book is an important manifesto that challenges the current zeitgeist that human functioning can be reduced to simple performance tests, decontextualized from the web of pressures and relationships to which we spend a lifetime trying to adapt.