Thank you to the British Academy for awarding John Duncan and myself research funds to test a key hypothesis in the cognitive neuroscience of human performance: is prefrontal cortex necessary for fluid intelligence?
We will use non-invasive brain stimulation (transcranial magnetic stimulation: TMS) to temporarily ‘deactivate’ the prefrontal cortex, and then measure the consequences for performance on standard tests of fluid intelligence. It is a relatively simple experimental design, but if done correctly, the results should provide important and novel insights into the brain mechanisms underlying one of the most important human faculties: flexible reasoning and problem solving.
My co-investigator, John Duncan, gained his reputation in the cognitive neuroscience of intelligence with his seminal brain imaging study published in Science. This research demonstrated that when people perform tasks that tax fluid intelligence, neural activity increases in the prefrontal cortex relative to control tasks that require less fluid intelligence.
This result suggests that the prefrontal cortex is involved in fluid intelligence - but of course, as every undergraduate in psychology/cognitive neuroscience should be able to tell you, brain imaging alone cannot tell us whether the activated brain area is in fact necessary for performing the task.
So, to verify the causal role of the prefrontal cortex, Duncan and colleagues next examined stroke patients (published in PNAS). The logic here is simple: does damage to the prefrontal cortex reduce fluid intelligence? But the methodology is not so simple. Of particular importance, how can you tell whether a patient has low IQ because of the brain damage, or whether they were always a low IQ individual?
Duncan's team tackled this problem by estimated pre-damage fluid intelligence from scores on other tests that measure so-called crystallised intelligence (e.g., vocabulary and general knowledge). Critically, crystallised intelligence reflects the life long achievements that depend on fluid intelligence during acquisition, and therefore can be used to approximate pre-damage fluid intelligence. If the prefrontal cortex is especially important for fluid intelligence, then damage should result in a disparity between fluid and crystallised intelligence. Indeed, this is what they found.
As developed in his popular science book, "How Intelligence Happens", Duncan suggests that the prefrontal cortex is essential for flexible structured cognitive processing, a key ingredient to fluid intelligence. If this theory is correct, then temporary deactivation of the prefrontal cortex should impair fluid intelligence. If not, then we need to rethink this working hypothesis.
What will these results tell us? Are we just heading back to 19th Century phrenology – associating discrete brain areas with complex high order human traits that are more like sociocultural inventions than principled neurocognitive constructs? Do we then plan to localise creativity here, insight there, and perhaps a little bit of moral judgment over here?
However, we must also recognise that we have to be careful how these results could be interpreted. Intelligence is a particularly sensitive area. The very concept of fluid intelligence often takes on more than it should - a reflection of the fundamental worth or even moral character of the individual.
Obviously there is some danger in reducing one of the most important cognitive mechanisms to a single number (e.g., intelligence quotient: IQ), which we can then compare between individuals and against groups. It is a dangerous business that can be exploited for any number of nefarious agendas. For example, we can try to confirm our own racial or sexist prejudices, conjuring up a biological, and therefore 'scientific' excuse for beliefs that are motivated by simple bigotry (recall the recent Watson controversy?). Conversely, on the other side, the same logic could be used to pursue an equality agenda. This could also be a dangerous path to follow - what if we are not all equal in ability? I see no a priori reason that there should not be group differences in any measure, including IQ. It is simply an empirical issue, and therefore a risky business to stake our sense of equality on equal ability.
IQ is certainly a loaded concept. Recently, I was speaking with a mathematician and historian about an advert they saw for a brain imaging study comparing IQ between academics from the sciences and humanities. The historian was intrigued, and eager to participate, whereas the mathematician was much more reluctant. I guess the risk of a lower-than-hoped-for score is quite disconcerting when your very livelihood depends on an almost mythical concept of pure intelligence, or better still - genius.
An anecdote comes to mind of a researcher who was to be the first subject in an fMRI study of IQ conducted by his colleagues. Being scanned can sometimes make people nervous the first time, but this was a seasoned neuroscientist, no stranger to the confined and uncomfortable space of an MRI. Rather, what made this no ordinary scanning experience was the fact that his respected colleagues were watching from the control room, monitoring his responses to the IQ task. Enough to make any academic uncomfortable!
This kind of awkwardness raises an important practical issue for us. Like many cognitive neuroscientists, I often rely on friends and colleagues to participate in my experiments, especially students, academic visitors, post-doctoral researchers. Obviously, one could easily imagine some tension arising in a lab that has tested everyone’s IQ. This could be particularly worrying for the more senior amongst us, as fluid intelligence is negatively correlated with age. We would not want to upset the natural order of the academic hierarchy!
Anyway, I will keep you posted how we get on with the project.