Working Memory, Intelligence and the Neural Efficiency Hypothesis

The brains of more intelligent people are capable of solving tasks more efficiently, which is why these people have superior cognitive faculties, or as Elsbeth Stern, Professor for Research on Learning and Instruction at ETH Zurich, puts it: “when a more and a less intelligent person are given the same task, the more intelligent person requires less cortical activation to solve the task.” Scientists refer to this as the neural efficiency hypothesis, although it ceased being a hypothesis quite some time ago and is now accepted by experts as an undisputed fact, with ample evidence to support it.

While working on her doctoral thesis in Stern’s work group, Daniela Nussbaumer also found evidence of this effect for the first time in a group of people possessing above-average intelligence for tasks involving what is referred to as working memory. “We measured the electrical activity in the brains of university students, enabling us to identify differences in brain activity between people with slightly above-average and considerably above-average IQs,” explained Nussbaumer. Past studies conducted to identify the effect of neural efficiency have generally used groups of people that exhibit extreme variations in intelligence.

Facial memory tested

Psychologists define working intelligence as a person’s ability to associate memories with new information as well as to adapt to changing objectives by filtering out information that has become irrelevant. The frontal lobe plays a pivotal role in these processes. In order to test these abilities, the ETH researchers asked 80 student volunteers to solve tasks of varying complexity on a computer.

One task, for example, was to determine whether individual letters or faces were part of a selection of letters or faces that had been shown to the subjects immediately beforehand. An especially difficult task involved identifying letters and faces shown to the subjects during past runs of the test within a time limit. While the students were completing the tests, the researchers used electroencephalography (EEG) to measure their brain activity. For the results analysis, the researchers had the subjects take a conventional IQ test and then split them into two groups: one with slightly above-average IQs and another with well above-average IQs.

Neural efficiency for moderately difficult tasks

The researchers found no differences in brain activity in either group of subjects when they performed very easy or very difficult tasks. They did, however, see clear differences in the case of moderately difficult tasks. Stern attributes this to the fact that none of the subjects had any trouble whatsoever with the simple tasks and that the difficult tasks were cognitively demanding even for the highly intelligent subjects. In contrast, all subjects succeeded in solving the moderately difficult tasks, but the highly intelligent subjects required fewer resources to do so.

This image shows a person with a EEG cap on, looking at a computer monitor with faces on it.
A subject solves a facial recognition task while EEG measurements of electrical activity in his brain are measured. Image credit: Fabio Bergamin / ETH Zurich.

Stern uses the analogy of a more and less efficient car: “When both cars are travelling slowly, neither car consumes very much fuel. If the efficient car travels at maximum speed, it also consumes a lot of fuel. At moderate speeds, however, the differences in fuel consumption become significant.”

Intelligence is not a muscle

So is it possible to use EEG measurements to draw any direct conclusions about intelligence? Stern qualifies the findings: “If you want to learn something about intelligence, you have to perform a conventional IQ test, because these tests still provide the most reliable results,” she says. EEG and other brain activity readings are not precise enough to assess the intelligence of an individual. Still, using these methods may be an interesting way to study how different levels of intelligence are manifested in the brain.

The ETH researchers’ intelligence study also suggests that it is impossible to “exercise” working memory. This has been a controversial issue among scientists in recent years because of contradictory findings in different studies. If subjects practise a certain task for a prolonged period, they improve with time. As Stern and her peers have now shown in their study, people who have practised certain tasks do not have any advantage over their unpractised counterparts when confronted with new, yet similar tasks.

About this neuroscience research

Source: Elsbeth Stern – ETH Zurich
Image Credit: The image is credited to Fabio Bergamin / ETH Zurich
Original Research: Abstract for “Neural efficiency in working memory tasks: The impact of task demand” by Daniela Nussbaumer, Roland H. Grabner, and Elsbeth Stern in Intelligence. Published online May 16 2015 doi:10.1016/j.intell.2015.04.004


Neural efficiency in working memory tasks: The impact of task demand

Studies of human intelligence provide strong evidence for the neural efficiency hypothesis, which suggests more efficient brain functioning (i.e., less or more focused activation) in more intelligent individuals. Recent studies have specified the scope of the neural efficiency hypothesis by suggesting that the relationship between brain activation and intelligence only holds true for problems of moderate difficulty and can be altered through training and is only found in frontal brain regions. We investigated the moderating roles of task difficulty and training on the neural efficiency phenomenon in the context of working memory (WM) training.

In two studies of 54 participants (study 1) and 29 participants (study 2), cortical activation was assessed by means of electroencephalography (EEG), or more precisely by means of event-related desynchronization (ERD) in the upper alpha band. ERD was assessed during the performance of WM tasks in a pre-test – training – post-test design, comparing groups of lower and higher intelligence.

We found supportive evidence for the neural efficiency hypothesis only in moderately difficult WM tasks in frontal brain regions, even in the absence of performance differences. There was no effect of intelligence on the simple or highly demanding, adaptive WM tasks. In the latter task, however, an intelligence-related difference emerged at the behavioral level, but training did not modulate the relationship between intelligence and brain activation.

These results corroborate the moderating role of task difficulty in the neural efficiency hypothesis in the context of WM demands and suggest that training does not impact the neural efficiency phenomenon in the context of WM demands.

“Neural efficiency in working memory tasks: The impact of task demand” by Daniela Nussbaumer, Roland H. Grabner, and Elsbeth Stern in Intelligence. Published online May 16 2015 doi:10.1016/j.intell.2015.04.004

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