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IQ and Brain


The brain is the most complicated, yet sophisticated organ of the human body and allegedly the most prized possession of the race called Homo sapiens. It is the chief control centre of the activities of the body and essentially the seat of all higher thought processes and intelligence.

But which part of the brain is precisely related to IQ? What is the 'brainy secret' of people boasting of a high IQ? Is it the cranial capacity, or the volume of gray matter, the number of grooves and crevasses undulating the brain surface, or simply the genes that influence the cryptic codes? Before we dive deeper, let me run you through a brief overview of the human mind

An overview of the Human Brain

The Human Brain can be divided into four primary regions: the brainstem, the cerebellum, the limbic system, and the cerebrum, which is regarded as the master brain.


Cerebrum denotes the right and left brain hemispheres. Each hemisphere contains four lobes (frontal, temporal, occipital, and parietal). The cerebral cortex is responsible for most "higher order" or intellectual brain functions such as thinking, reasoning, judging, planning, voluntary movement, and overall behavior.

  1. Frontal Lobe- associated with reasoning, planning, parts of speech, movement, emotions, and problem solving.
  2. Parietal Lobe- associated with movement, orientation, recognition, perception of stimuli.
  3. Occipital Lobe- associated with visual processing.
  4. Temporal Lobe- associated with perception and recognition of auditory stimuli, memory, and speech.

Which part of the brain is related to IQ?

Cortex width fluctuations

Dr. Judith Rapoport of the National Institute of Mental Health in Bethesda, reports that "IQ is related to the dynamics of cortex maturation."

In their most comprehensive structural brain-scan study of intelligence, UC Irvine College of Medicine researchers assert that general human intelligence is influenced by the volume of gray matter tissue in certain regions of the brain.

Brain scans reveal that the brain's outer coat, the cortex, thickens more rapidly during childhood, reaching its peak thickness relatively late (perhaps reflecting a longer development time for high-level thinking), while during the late teens, the cortex normally thins rather than thickens, in what scientists believe is a drying up of redundant circuitry.

The smartest 7-year-olds tended to start out with a thinner cortex that thickened rapidly, peaking by age 11 or 12 before thinning. In average-IQ children, an initially thicker cortex peaked by age 8, with gradual thinning soon after, such that the time for honing of specific faculties was markedly reduced.

The above helps resolve some occult issues as to why some people are quite good at mathematics and not so good with their spelling, and another person, with the same IQ, has have different set of abilities.

Variance with age

Researchers have also highlighted, that the relationship between cortex thickness and IQ varied with age, especially in the prefrontal cortex, seat of abstract reasoning, planning, and related operations known as "executive" functions. "People with very agile minds tend to have a very agile cortex," said the institute's Philip Shaw, a member of the research team.

Pattern determines IQ

Dr. Richard Haier, professor of psychology in the Department of Pediatrics and long-time human intelligence researcher, and his team at UCI and the University of New Mexico used MRI to obtain structural images of the brain in 47 normal adults who were made to take a standard intelligence quotient tests.

The results underscored that "gray matter in specific regions in the brain displays greater co-relation to IQ than overall brain size. Multiple brain areas are related to IQ, and a mosaic of their combinations account for IQ scores." Therefore, it is likely that a person's mental fortes and pitfalls depend to a large extent on the individual's blueprint of gray matter spread

"Did you know that only about 6 percent of all the gray matter in the brain appears related to IQ."

The findings also propose that the brain areas where gray matter is related to IQ show disparity between young-adult and middle-aged subjects. In middle age, more of the frontal and parietal lobes are related to IQ; while in younger adults, less of frontal and more of temporal areas are involved.

Sex Differences

In general, men have approximately 6.5 times the amount of gray matter related to general intelligence than women, and women have nearly 10 times the amount of white matter related to intelligence than men. Gray matter realms are information processing centers in the brain, while the white matter are the networking hubs, establishing connections between these processing centers.

This information helps explain why men tend to excel in tasks requiring more local processing (like mathematics), while women are better inclined at integrating and assimilating information from distributed gray-matter regions in the brain, such as required for coherent language.

Study suggests that in men, only anterior cerebral area correlated with IQ, while in women, total and posterior cerebral areas were correlated with IQ.

Size does or doesn't matter?

Since the time of Paul Broca (1824-1880) and Sir Francis Galton (1822-1911) assiduous attempts have been made to answer the question whether brain size plays a role in determining intelligence.For example, Galton (1888) reported that the head size of Cambridge Class A students was about 3.3% larger than those of Class B students.An overall correlation of 0.44 was found between MRI-measured-brain-size and IQ in 8 separate studies with a total sample size of 381 non-clinical adults.

A 'BBC' document broadcasted recently, had studied people with very high IQ and compared them to one another, along with some average IQ persons. One factor they measured was the brain size (as well as the amount of grey matter), and surprisingly the guy who aced the IQ charts and other intelligence tests had the smallest brain and lowest amount of grey matter amongst the whole test population.

Scientists argued that his IQ was actually due to the commendably efficient "wiring" of his neurons, and that the brain size had very little to do with intelligence.

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