Where logic lives: Brain region responsible for reasoning revealed

A team of researchers has recently identified the right frontal lobe as a vital part of logical thinking and the ability to tackle new problems.

The study reveals that when the right brain is damaged, people’s capacity for reasoning suffers, implying that this area is central to our day-to-day cognitive functions.

The research was led by experts at University College London (UCL) and University College London Hospitals (UCLH).

Damage to the right frontal lobe

Scientists have long used functional imaging (fMRI) to study cognition in healthy individuals. These studies, however, only show correlations rather than proving which parts of the brain are essential.

To pinpoint causation, experts rely on lesion-deficit mapping, a technique that examines how specific types of brain damage affect behavior.

Finding sufficient patients with carefully localized right frontal lobe damage can be challenging. The research team overcame that hurdle by enrolling 247 patients with unilateral focal brain lesions (either in the left or right, frontal or posterior regions).

Another 81 healthy adults served as a baseline for comparison. By systematically observing what happens when parts of the brain are damaged, the team could identify the areas indispensable for particular cognitive skills.

Measuring the brain’s reasoning ability

To measure logical reasoning, the researchers created two original tests. One verbal analogical reasoning task asked participants to determine relationships between words.

A question might read: “If Sarah is smarter than Diana, and Sarah is smarter than Heather, is Diana smarter than Heather?” Such questions test one’s ability to deduce logical conclusions from given statements.

The second was a nonverbal deductive reasoning task that required spotting patterns or similarities among shapes, pictures, or numbers.

One sample query stated: “Which set of numbers is 1, 2, 3 most similar to 5, 6, 7 or 6, 5, 7?” The goal was to see how patients reason about relationships without relying on language.

Right brain is essential for reasoning

When the researchers compared test results, one detail stood out: patients with injuries in the right frontal lobe scored significantly worse on both tests than those with lesions in other areas. These patients were about 15% more prone to errors than their counterparts and the healthy controls.

This outcome supports the idea that the right brain is essential for reasoning. It’s especially important when interpreting novel information and drawing logical conclusions.

Lead author Joseph Mole of the UCL Queen Square Institute of Neurology and Department of Neuropsychology emphasized the importance of these findings in spotting reasoning issues early.

“Our study explores how the front right part of the brain helps people think and solve new problems,” said Mole. “It also shows that our two new tests can help detect reasoning problems in individuals with brain damage, improving diagnosis and treatment.”

Ties to fluid intelligence

Another important takeaway involves what neuroscientists call fluid intelligence – our capacity to solve problems in new or unfamiliar situations.

Senior author Lisa Cipolotti, a professor in the same institute at UCLH, noted that the study shows a substantial overlap between the brain networks responsible for fluid intelligence and reasoning. Both networks appear to rely heavily on the right frontal lobe.

The experts used advanced lesion mapping techniques developed by Professor Parashkev Nachev and colleagues at the UCL Queen Square Institute of Neurology. These tools made it possible to explore precisely which portions of the frontal lobe, when damaged, most affect reasoning.

Implications for neurological care

The practical impact is significant. Brain injuries from strokes or tumors can affect daily life in subtle ways. These injuries require the early identification of cognitive deficits.

Many neurological assessments miss right frontal lobe dysfunction because standard tests often focus on memory, language, or motor skills. By contrast, the tasks introduced here specifically examine higher-order reasoning.

The researchers hope that once validated further, these tests can be integrated into clinical settings. For patients, that means more thorough evaluations and, potentially, more focused rehabilitation programs.

If doctors know that a person’s right frontal region has sustained damage, they can anticipate potential problems in logical thinking and develop strategies. This type of cognitive training or specialized therapy will help patients manage symptoms.

More right-brain studies are needed

Future studies may refine the new tasks to confirm their effectiveness. Additional testing will also detect right-brain deficits across a wider range of patient populations.

Researchers also aim to examine whether training that targets reasoning skills can bolster recovery, potentially improving quality of life for people with frontal lobe injuries.

As this line of research advances, the main lesson is clear: while multiple parts of the brain support different aspects of cognition, the right frontal lobe’s role in reasoning appears especially vital.

For anyone dealing with brain damage – or anyone working to help those who are – this knowledge reshapes how we assess, treat, and ultimately understand the very nature of human thought.

The study is published in the journal Brain.

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