20 June 2000

Human Brain Applies Law Of Least Effort When Solving Problems

by Kate Melville

Using brain imaging, scientists at Carnegie Mellon University have discovered how the human brain goes to work on solving a problem and how it employs surprising economies of effort in the process.

The results, compiled by Psychology post-doctoral research associate Erik Reichle and Professors Patricia Carpenter and Marcel Just, all of Carnegie Mellon's Center for Cognitive Brain Imaging (http://www.ccbi.cmu.edu), appear in the June issue of Cognitive Psychology.

The Carnegie Mellon scientists found that the law of least effort may apply to the brain. Their results indicate that partially separate networks within the human brain support language and visual-spatial processing. The Carnegie Mellon findings also suggest that our brains may seek to minimize the mental workload by choosing the strategy that makes less work for the brain.

By studying thinking in a simple task that lends itself to either a visual or a verbal solution, the researchers were able to identify which of two strategies was being used. The findings are based on functional magnetic resonance imaging (fMRI) scans showing that brain function associated with a verbal strategy produced relatively more activation in a network of brain areas specialized for language processing, prominently including Broca's area, which governs the ability to talk. The use of a visual strategy shifted the activation towards a network of brain areas that process visual and spatial information, particularly the parietal cortex.

"The new findings demonstrate that different ways of thinking engage different networks of brain areas, resulting in identifiable brain activation patterns in each individual," Just said. "We can't quite read a person's mind by watching their brain at work, but we can reliably tell which way a person is thinking about a problem."

The study measured brain activity in college students as they read sentences such as "The star is not above the plus (sign)" and judged whether the sentences were true or false of an accompanying simple picture. The student participants were instructed on the use of both a verbal and a visual strategy, and told when to use each one. Comparing the meaning of a sentence to the content of a picture involves both verbal and spatial thinking, and the comparison of their meaning can be done in either a verbal or a spatial domain of thought.

The Carnegie Mellon team also was surprised that the amount of brain activation occurring with each strategy depended on how skilled the participant was in that kind of thinking. Carpenter explained that more skill was associated with less activation, just as more skill at something physical like swimming results in less muscle activity to perform a given task.

"Individuals with better verbal skills had less activation in Broca's area when they used the verbal strategy. Similarly, individuals with better visual-spatial skills had less activation in the left parietal cortex when they used the visual-spatial strategy," she added.

These findings tie in with one of the Center for Cognitive Brain Imaging's main goals of using brain imaging to determine not only which parts of the brain are used for this or that task, but to also discover the mental economics that dictate how the organization of brain areas ends up dealing with a particular thinking task.

"In the final analysis the brain is a biological system that does its job by consuming biological resources and providing a service, namely thinking or information processing," Just said. "But when there is a choice of how to provide the service, mental economics may come into play, with the brain using the method that is less costly for that individual, namely the one in which he or she is more efficient."

The researchers noted that this finding provides a possible meeting ground between the brain and the mind -- relating the dynamics of higher level thinking (in this case understanding of sentences and pictures) and the dynamics of brain-level activity (how the brain accomplishes the translation between the two domains of understanding).

Because not all brains are alike in their efficiency at a given task, one of the new directions these results may lead to is in evaluating which method, verbal or visual, may be more effective for instruction or communication for a given individual. The new results show that choice is more than just a matter of taste; it is a matter of mental efficiency.