©Arlene Taylor PhD
Sometime after the sixth week of pregnancy, the chemical-hormonal mix to which the developing fetal brain is exposed may change based on the chromosomes present and/or based on available androgens in the mother’s body. If there is a “Y” chromosome present it calls for the mother’s androgens to give the brain a chemical bath. The process is designed to change the brain from the default position into what society calls a male brain.
This chemical bath results in a number of changes to the fetal brain, including:
- Turns the brain a lavender color temporarily
- Slows the maturation of left hemisphere and allows the right hemisphere to flourish
- Modifies the corpus callosum
- Alters the size in 12 identified areas (9 areas are larger in male brain)
- Changes the structure of the inner ear
A large bundle of horizontal nerve fibers connects the right and left hemispheres of the brain. These commissure tracks contain axons that conduct nerve impulses. This permits one hemisphere to know what is going on in the other, and enables them to collaborate and work together. Metaphorically, compare this to a bridge that has two layers or decks (much like The Bay Bridge that connects San Francisco with the East Bay has two decks). One deck is known as the Corpus Callosum, the other as the Anterior Commissure (a more primitive connection that links subconscious areas of the cerebral hemispheres).
Studies have shown a difference in the size of the anterior commissure between male and female brains.
• The anterior commissure is larger in the female brain
• The anterior commissure is smaller in the male brain
Studies have shown a difference in the size of the corpus callosum between male and female brains, as well, but controversy exists about magnitude.
The corpus callosum may be relatively larger in some female brains both from gestational development and from an earlier onset of puberty, as is the anterior commissure. A larger corpus callosum, with up to 40% more connecting fibers shown in some studies, contributes to a more generalized style of processing information (e.g., female brain is generally better equipped to integrate left and right hemisphere thinking). The female brain also has more tissue in the Massa intermedia that connect the two halves of the thalamus (a sort of relay station that directs information for further processing).
The corpus callosum in the male brain consists of relatively fewer connecting fibers of smaller diameter. This probably results both from its gestational chemical bath and a later onset of puberty (see illustration below).
Cutaway showing a larger corpus callosum in the female brain
Cutaway showing a smaller corpus callosum in the male brain
The corpus callosum in the female brain is thicker, consisting of a higher number of connecting fibers of larger diameter. There may be several contributing factors:
The corpus callosum in the male brain has fewer connecting fibers of smaller diameter. There may be several contributing factors:
In a study of blindfolded right-handed boys and girls, each was given two objects to hold: one in each hand. The objects were then removed and mixed in with other similar items. The blindfolds were removed and the children were asked to select the objects they had held in their hands.
Boys were more accurately able to identify objects held in their left hands (processed by their spatial right hemisphere.) Girls were able to identify objects held in either hand with the same degree of accuracy. In a similar way, the lateral transmission between the hemispheres through the Corpus Callosum allows the female brain to quickly consult all of her past experience when processing information and making decisions. In most cases, the female brain can do this faster and arrive at an answer more quickly than does the male brain, sometimes giving an almost instantaneous response.
NOTE: Fewer women are left-handed. Even when left-handed, however, they tend to use the right hemisphere less efficiently than comparable males (perhaps because of a tendency toward a generalized style of processing information). More males are left-handed. Left-handed males tend to be more concrete, pictorial, affective, and verbal. They are also more likely to suffer from learning disabilities, immune diseases, and migraine headaches.
Hemispheric Connections and Energy
One of the first things of interest to note when discussing functional differences between male and female brains is that, second for second, female brains require more energy to run (e.g., utilize more oxygen, glucose, and micronutrients). Perhaps that is because if any part of the brain is on, all parts are on, the female brain being more generalized in processing style. This means that when a male and a female brain are collaborating on the same problem, given that the brains are similar in age, education, and experience, the female brain will utilize more energy and may tire more quickly.
Male brains, on the other hand, tend to be more lateralized in processing style. That is, part of the brain can be more energy-efficient for selected tasks (e.g., one part is working while others are idling). This makes the brain more energy efficient second for second. The lateralization processing style of the male brain is related to the uniqueness of its corpus callosum; the generalized processing style of the female brain is related to the uniqueness of its corpus callosum.
• Metabolic rates in the cortex are identical in both genders.
• Females have higher metabolic rates in the portion of the emotional brain that anticipates and handles symbolic processing.
• Males have higher metabolic rates in the so-called older limbic system (e.g., the portion of the emotional brain that handles gut reactions).
• Males tend to activate different areas of the brain (from females) both when thinking and at rest.
Metaphorically, a generalized versus lateralized processing style can be compared to a six-lane freeway versus a two-lane highway. With their six-lane corpus-callosum freeway, females tend to spend a lot more time on the road, so to speak. They engage in multiple tasking, quickly alternating their attention from one task to another.
The male brain, on the other hand, prefers to complete a task in one area of the brain prior to getting out onto its two-lane corpus-callosum highway and traveling to another area. This can be a source of conflict for cross-gender couples if the female asks the male to “drop everything and help me,” when he isn’t ready to change concentration. The male, on the other hand, may be very critical of the female who “doesn’t completely finish one task before jumping to another.”
Intuition and Female Sixth Sense
Introduce the topic of intuition into almost any group and you just signed on for a lively conversation. Some don’t believe intuition even exists. Others think it probably does but don’t think they’re particularly intuitive. Still others have honed their sense of intuition and use it regularly.
The function of intuition is believed to be located in the right frontal lobe of the thinking brain. Therefore, individuals who prefer to use the right frontal lobe are often very intuitive (have hunches) in regard to new ideas and products, male or female.
Because of its generalized style of processing the female brain has an additional type of intuition, called the sixth sense of intuitive knowing by some. This means that females are often better at sensing the difference between what people actually say and what they really mean. They can pick up, as it were, vibrations of a very short wavelength almost as soon as they are generated. They can also readily assimilate the information absorbed, even peripherally, from the environment. At times, however, females have been socialized to discount this intuitive sense, often to their detriment.