Haier’s P-FIT Theory Links Myelin to Higher IQ and Brain Efficiency

A review of decades of neurobiology research challenges the notion that higher intelligence requires more mental horsepower. Richard Haier’s 1988 study—the first to combine brain imaging with IQ testing—found that smarter individuals actually burn less brain energy when solving problems. This Neural Efficiency Hypothesis (NEH) posits that intelligent brains have higher signal-to-noise ratios, using fewer but more targeted circuits. Haier’s 1992 follow-up showed that during learning, expert subjects quickly narrow neural activation to efficient patterns, while less intelligent brains persist with wasteful, incorrect solutions that must be inhibited by frontal areas like the anterior cingulate cortex.

Building on NEH, Haier and Jung’s 2007 Parietal-Frontal Integration Theory (P-FIT) identifies white matter tracts—especially myelinated axons—as the structural backbone of intelligence. Myelin speeds signal transmission and reduces crosstalk, enabling the efficient integration of parietal sensory regions with frontal executive areas. Evolutionary studies confirm white matter expansion distinguishes human brains from other primates, while neurodegenerative diseases that degrade myelin (e.g., multiple sclerosis) directly reduce fluid IQ. Together, the evidence positions myelination as a key biological determinant of individual intelligence differences, not just computational power but computational efficiency.