11.2018 | THE SCIENTIST 33els see it as an average or summation of
cognitive abilities, not a cause.
Last year, University of Cambridge neuro-
scientist Rogier Kievit and colleagues pub-
lished a study that suggests IQ is an index
of the collective strength of more-specialized
cognitive skills that reinforce one another.
The results were based on vocabulary and
visual reasoning test scores for hundreds of
UK residents in their late teens and early 20s,
and from the same subjects about a year and
a half later. With data on the same people at
two time points, Kievit says, the researchers
could examine whether performance on one
cognitive skill, such as vocabulary or reason-
ing, could predict the rate of improvement in
another domain. Using algorithms to predict
what changes should have occurred under
various models of intelligence, the research-
ers concluded that the best fit was mutualism,
the idea that different cognitive abilities sup-
port one another in positive feedback loops.
In 2016, Andrew Conway of Claremont
Graduate University in California and Kristóf
Kovács, now of Eötvös Loránd University in
Hungary, made a different argument for the
involvement of multiple cognitive processes
in intelligence. In their model, application-
specific neural networks—those needed for
doing simple math or navigating an environ-
ment, for example—and high-level, general-
purpose executive processes, such as break-
ing down a problem into a series of small,
manageable blocks, each play a role in help-
ing a person complete cognitive tasks. It’s the
fact that a variety of tasks tap into the same
executive processes that explains why indi-
viduals’ performance on disparate tasks cor-
relates, and it’s the average strength of these
higher-order processes, not a singular ability,
that’s measured by g, the researchers argue.
Neuroscientists might make more progress in
understanding intelligence by looking for the
features of the brain that carry out particular
executive processes, rather than for the seat
of a single g factor, Kovács says.
As researchers grapple with the intrac-
table phenomenon of intelligence, a phil-
osophical question arises: Is our species
smart enough to understand the basis of
our own intelligence? While those in the
field generally agree that science has a long
way to go to make sense of how we think,
most express cautious optimism that the
coming decades will yield major insights.
“We see now the development, not
only of mapping brain connections in
human beings... we’re also beginning to
see synapse mapping,” Haier says. “This
will take our understanding of the basic
biological mechanisms of things like
intelligence... to a whole new level.” gUPPING IQ
The idea of manipulating intelligence is enticing, and there has been no shortage of efforts to do just that. One tactic that once seemed to hold
some promise for increasing intelligence is the use of brain-training games. With practice, players improve their performance on these simple
video games, which rely on skills such as quick reaction time or short-term memorization. But reviews of numerous studies found no good
evidence that such games bolster overall cognitive abilities, and brain training of this kind is now generally considered a disappointment.
Transcranial brain stimulation, which sends mild electrical or magnetic pulses through the skull, has shown some potential in recent
decades for enhancing intelligence. In 2015, for example, neurologist Emiliano Santarnecchi of Harvard Medical School and colleagues
found that subjects solved puzzles faster with one type of transcranial alternating current stimulation, while a 2015 meta-analysis found
“significant and reliable effects” of another type of electrical stimulation, transcranial direct current stimulation (Curr Biol, 23:1449–53).
While magnetic stimulation has yielded similarly enticing results, studies of both electrical and magnetic stimulation have also raised
doubts about the effectiveness of these techniques, and even researchers who believe they can improve cognitive performance admit that
we’re a long way from using them clinically. (See “Flash Memory” on page 17.)
One proven way researchers know to increase intelligence is good old-fashioned education. In a meta-analysis published earlier this
year, a team led by then University of Edinburgh neuropsychologist Stuart Ritchie (now at King’s College London) sifted out confounding
factors from data reported in multiple studies and found that schooling—regardless of age or level of education—raises IQ by an average
of one to five points per year (Psychol Sci, 29:1358–69). Researchers, including University of British Columbia developmental cognitive
neuroscientist Adele Diamond, are working to understand what elements of education are most beneficial to brains.
“Intelligence is predictive of a whole host of important things,” such as educational attainment, career success, and physical and mental
health, Ritchie writes in an email to The Scientist, “so it would be extremely useful if we had reliable ways of raising it.”
References- J. Flynn, “Massive IQ gains in 14 nations: What IQ
tests really measure,” Psychol Bull, 101:171-91, 1987. - J.A. Kaminski et al., “Epigenetic variance
in dopamine D2 receptor: A marker of IQ
malleability?” Transl Psychiat, 8:169, 2018. - R.E. Jung, R. J. Haier, “The parieto-frontal
integration theory (P-FIT) of intelligence:
Converging neuroimaging evidence,” Behav Brain
Sci, 30:135–87, 2007. - M. Lundqvist et al., “Gamma and beta bursts
during working memory readout suggest roles in
its volitional control,” Nat Comm, 9:394, 2018. - A.K. Barbey, “Network neuroscience theory of
human intelligence,” Trends Cogn Sci, 22:8–20, 2018. - E. Santarnecchi, S. Rossi, “Advances in the
neuroscience of intelligence: From brain
connectivity to brain perturbation,” Span J
Psychol, 19:E94, 2016. - J. J. Lee et al., “Gene discovery and polygenic
prediction from a genome-wide association
study of educational attainment in 1.1 million
individuals,” Nat Genet, 50:1112–21, 2018. - R. Plomin, S. von Stumm, “The new genetics of
intelligence,” Nat Rev Genet, 19:148–59, 2018. - J.E. Savage et al., “Genome-wide association
meta-analysis in 269,867 individuals identifies new
genetic and functional links to intelligence,” Nat
Genet, 50:912–19, 2018. - R.A. Kievit et al., “Mutualistic coupling between
vocabulary and reasoning supports cognitive
development during late adolescence and early
adulthood,” Psychol Sci, 28:1419–31, 2017. - K. Kovács, A.R.A. Conway, “Process overlap
theory: A unified account of the general factor of
intelligence,” Psychol Inq, 27:151-177, 2016.