Brain theories about the basis of high level reasoning and problem solving are not so advanced. Neuroim-aging studies in this area are more exploratory. For example, in 1988 Haier and colleagues published a PET study of GMR in normal volunteers while they performed a difficult test of abstract reasoning, the Raven's Advanced Progressive Matrices (RAPM). The RAPM is a standard test that requires the subject to solve 36 problems, each one comprised of a series of nine symbols arranged in a pattern. One symbol, however, is always missing from the pattern. Once the subject understands the pattern, the missing symbol can be selected from eight possible choices. Scores on the RAPM are highly correlated with IQ. Surprisingly, this study found an inverse relationship between RAPM scores and brain GMR. The subjects with high RAPM scores (i.e., good performance) had lower GMR, especially in the temporal lobe. This was interpreted as evidence that the efficiency of brain energy use was more important for good cognitive performance on this complex task than the level of GMR. Whether brain efficiency involves task strategy, mental effort, characteristics of individual neurons, or other parameters has yet to be determined. Other PET research also reports inverse relationships between performance on
Brain Scanning/Neuroimaging complex tasks and brain function. A study of mild retardation and Down Syndrome reported by Haier and colleagues in 1995 showed higher brain GMR in both groups compared to matched controls. They speculated that a failure of normal developmental neural pruning could be the basis for a person having too many synaptic connections and redundant brain circuitry resulting in inefficient problem solving, low IQ, and high GMR. Standard score images for each retarded subject revealed considerable heterogeneity of GMR patterns. In the same study, MRI was used to measure brain volume. For the combined samples of mildly retarded, Down Syndrome, and controls, there was an inverse relationship between GMR and IQ and an inverse relationship between GMR and brain volume. There also was a positive relationship between brain size measured by MRI and IQ, consistent with many other studies. Clearly, the use of brain imaging to study complex reasoning in humans has potential for elucidating the biological basis of problem solving and individual differences in intelligence. At this stage, sophisticated theoretical formulations for hypothesis testing are awaiting the accumulation of additional empirical observations.
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