PALABRAS CLAVE

Clancy Blair (Nisbett et al., 2012) shows that locating different cognitive functions in different brain areas is possible. He cites the study that found that the hippocampi (seat of navigating through three-dimensional space) of taxi cab drivers enlarged in proportion to their time on the job (Maguire et al., 2000). Three months of playing the visual-spatial game Tetris gave increased cortical thickness in two regions and brought functional changes in other areas. Three months of juggling increased the size of grey matter in the mid-temporal and left-posterior areas. Three months after juggling ceased, some expansion was lost. Figure 3

maps the WAIS cognitive functions on areas of the brain, and offers comments about the effects of aging on those areas.

It looks as if we can do a reasonable job of mapping for Analytic and Verbal Abilities. I do not know the potency of the technology available to survey the brain. I am told that MRI

sensorimotor area frontal eye field

frontal lobe

prefrontal area Broca’s area (in left hemisphere)

temporal lobe

auditory auditory association (including Wernicke’s area, in left hemisphere)

visual association

visual parietal lobe

Figure 3 Areas of the brain associated with WAIS indexes. 1. Verbal Comprehension: Broca’s area (rear of frontal lobe) and

Wernicke’s area (mid-temporal lobe). Aging: The only regions of the brain to show prominent grey matter increase into adulthood.

2. Working Memory: The WAIS measures this using arithmetic (which involves remembered knowledge) and digit span (part of which involves simple recall), so several areas come into play. Aging: Areas too diverse to estimate.

3. Analytic or fluid intelligence: Prefrontal area. Aging: Earliest region to show age-related decline.

4. Processing Speed: Perhaps the central nervous system

(associated with decline in motor function). Aging: Later than the prefrontal area.

Sources: AFAR, 2009, p. 2; Resnick, Lamar, & Driscoll, 2007, p. 562; Sowell, Thompson, & Toga, 2004, p. 390.

(Magnetic Resonance Imaging) has great promise in determining which areas are active during various kinds of cognition. I am told that PET scans (Positron Emission Tomography) have shown age-related decline in the effects of dopamine and the condition of axons. Perhaps it is capable of discriminating between the rates of loss in neural plasticity and rates of myelin thinning of high-performing and average-performing subjects respectively, and can do so this for the analytic areas on the brain map. Others more sophisticated than I will know what is possible and what to look for.

Merely because there is a verbal bonus, we must not assume that we will find no physiological tendency for high- performing verbal brains to require more maintenance with age than low-performing verbal brains. It is possible that a growing verbal exercise gap between the bright and the aver- age after retirement swamps a slight tendency in that direc- tion. However, the analytic and verbal areas of the brain do show a different profile with age. As Figure 3 notes, the ver- bal areas are the only ones that show real grey matter increase into adulthood, and the analytic area is the first to show age- related decline.

Presumably, throughout human evolution, the main rea- son people survived past the age of procreation was because of the help they could give to their own grandchildren (thus per- petuating genes advantageous for longevity). Perhaps their child- minding roles required the persistence of Verbal Ability but placed little premium on Analytic Ability. If so, there would be little evolutionary pressure to eliminate a trade-off between high performance and high maintenance for Analytic Ability that manifests itself only in old age. It may even be that the less one analyzes one’s lot when child-minding, the more chance there is of preserving one’s sanity.

Whatever the role of environment and physiology, some- thing seems to be levying a bright tax on our Analytic Ability:

intelligent minds do worse in the struggle against age. The ideas they create are another matter. If these tip the balance in favor of truth over falsehood, they bequeath an inheritance as timeless as our eternal adversary.

This chapter has been mainly a puzzles chapter rather than a progress chapter. But it would be very boring if soci- ology, psychology, and brain physiology had no new problems to solve. If the evidence stands up, the growing adult/child vocabulary gap and the bright tax will put a premium on expertise in all three.

Race and gender IQ differences arouse strong emotions and there- fore I excluded them from What Is Intelligence? I did not want critical assessment of my views on intelligence lost in a welter of acrimonious debate. Look at what happened to The Bell Curve, which was 90 percent about other subjects and debated as if it were 90 percent about race.

I have offered my case that the black/white IQ gap is prob- ably environmental in origin elsewhere (Flynn, 1980, 2008), and will not repeat it here. However, much of this book preaches the message that differences between Wechsler subtests are central to interpreting IQ trends. The following will, I hope, show that these subtest differences are not central to the race and IQ debate, at least not for the reasons given by thinkers such as Jensen and Rushton. As a bonus, we may enhance our understanding of why WISC subtests differ in a variety of ways: not only in the size of the black/white performance gap, but also in terms of their

g-loadings, heritability, and sensitivity to inbreeding depression.