A new British study led by researchers from the Queen Square Institute of Neurology at University College London (UCL) and the National Hospital for Neurology and Neurosurgery at University College London Hospital (UCLH) have identified the brain area necessary for fluid intelligence – the ability that the authors describe as "arguably the defining feature of human cognition".
Fluid intelligence is what supports our ability to solve problems without prior experience. It is thought to be a key feature involved in "active thinking" – the set of complex mental processes involved in abilities such as abstraction, judgment, attention, strategy generation, and inhibition – as used in everyday activities from organising a party to filling out a tax return. Fluid intelligence correlates with many cognitive abilities, including memory, and predicts educational and professional success, social mobility, health, and longevity.
'Central Role in Human Behaviour'
"Despite its central role in human behaviour, fluid intelligence remains contentious with regards to whether it is a single or a cluster of cognitive abilities, and the nature of its relationship with the brain," the researchers said. Studies rely on 'lesion-deficit mapping' of the brain in patients with brain areas that are either missing or damaged, to establish which parts are necessary for particular abilities. These are difficult to conduct because of the challenge of identifying and testing patients with focal brain injury. Consequently, previous studies have mainly used functional imaging (fMRI) techniques – which can be misleading – and were almost all small, methodologically constrained, and inconclusive.
In their new observational study, published in Brain, the scientists investigated 227 patients who had suffered either a brain tumour or stroke causing unilateral brain lesions, and compared their performance with that of 165 healthy controls using the best-established test of fluid intelligence, Raven's Advanced Progressive Matrices (APM). The test contains multiple choice visual pattern problems of increasing difficulty, each presenting an incomplete pattern of geometric figures requiring the subject to select the missing piece from a set of multiple possible choices.
Modelling 'a Brain Map of Cognitive Abilities'
They then used an array of lesion-deficit inferential models responsive to the potentially distributed nature of fluid intelligence to map the intricate anatomical patterns of common forms of brain injury, and disentangle functional from confounding pathological distributed effects. This approach treated the relations between brain regions as a mathematical network whose connections described the tendency of regions to be affected together, either because of the disease process or in reflection of common cognitive ability. This allowed them to determine the relationship between patients' performance on the APM task and the patterns of damage from their injuries, so producing a brain map of cognitive abilities.
The researchers reported that impaired fluid intelligence was largely confined to patients with frontal lesions, and was more marked with lesions on the right than on the left, whereas patients with non-frontal lesions were indistinguishable from controls and showed no modulation by laterality.
They said that their study represented "the first large-scale investigation of the distributed neural substrates of fluid intelligence in the focally injured brain". They concluded that combining novel graph-based lesion-deficit mapping with detailed investigation of cognitive performance in a large sample of patients provided "crucial information about the neural basis of intelligence" and indicated that "a set of predominantly right frontal regions, rather than a more widely distributed network, is critical to the high-level functions involved in fluid intelligence".
Right Frontal Brain Regions 'Critical to High-level Functions'
Lead author Prof Lisa Cipolotti from Queen Square said: "Our findings indicate for the first time that the right frontal regions of the brain are critical to the high-level functions involved in fluid intelligence, such as problem solving and reasoning.
"This supports the use of APM in a clinical setting, as a way of assessing fluid intelligence and identifying right frontal lobe dysfunction.
"Our approach of combining novel lesion-deficit mapping with detailed investigation of APM performance in a large sample of patients provides crucial information about the neural basis of fluid intelligence. More attention to lesion studies is essential to uncover the relationship between the brain and cognition, which often determines how neurological disorders are treated."
The study was funded by Welcome and the NIHR UCLH Biomedical Research Centre funding scheme. Researchers also received funding from The National Brain Appeal and the Guarantors of Brain.
