Major new study from Cambridge University just out: male and female brains are different.PC feminists won't like it

(Cambridge)(h/t CHSummers) New study examines thousands of brains from two decades of research to reveal differences between male and female brain structure.

For the first time we can look across the vast literature and confirm that brain size and structure are different in males and females

Amber Ruigrok

Reviewing over 20 years of neuroscience research into sex differences in brain structure, a Cambridge University team has conducted the first meta-analysis of the evidence, published this week in the prestigious journal Neuroscience and Biobehavioral Reviews. 

The team, led by doctoral candidate Amber Ruigrok and Professors John Suckling and Simon Baron-Cohen in the Department of Psychiatry, performed a quantitative review of the brain imaging literature testing overall sex differences in total and regional brain volumes. They searched all articles published between 1990 and 2013. A total of 126 articles were included in the study, covering brains from individuals as young as birth to 80 years old.

They found that males on average have larger total brain volumes than women (by 8-13%). On average, males had larger absolute volumes than females in the intracranial space (12%; >14,000 brains), total brain (11%; 2,523 brains), cerebrum (10%; 1,851 brains), grey matter (9%; 7,934 brains), white matter (13%; 7,515 brains), regions filled with cerebrospinal fluid (11.5%; 4,484 brains), and cerebellum (9%; 1,842 brains). Looking more closely, differences in volume between the sexes were located in several regions. These included parts of the limbic system, and the language system.

Specifically, males on average had larger volumes and higher tissue densities in the left amygdala, hippocampus, insular cortex, putamen; higher densities in the right VI lobe of the cerebellum and in the left claustrum; and larger volumes in the bilateral anterior parahippocampal gyri, posterior cingulate gyri, precuneus, temporal poles, and cerebellum, areas in the left posterior and anterior cingulate gyri, and in the right amygdala, hippocampus, and putamen.

By contrast, females on average had higher density in the left frontal pole, and larger volumes in the right frontal pole, inferior and middle frontal gyri, pars triangularis, planum temporale/parietal operculum, anterior cingulate gyrus, insular cortex, and Heschl’s gyrus; bilateral thalami and precuneus; the left parahippocampal gyrus, and lateral occipital cortex.

The results highlight an asymmetric effect of sex on the developing brain. Amber Ruigrok, who carried out the study as part of her PhD, said: “For the first time we can look across the vast literature and confirm that brain size and structure are different in males and females. We should no longer ignore sex in neuroscience research, especially when investigating psychiatric conditions that are more prevalent in either males or females.”

Professor Suckling added: “The sex differences in the limbic system include areas often implicated in psychiatric conditions with biased sex ratios such as autism, schizophrenia, and depression. This new study may therefore help us understand not just typical sex differences but also sex-linked psychiatric conditions. It is important to note that we only investigated sex differences in brain structure, so we cannot infer anything about how this relates to behaviour or brain function. Integrating across different levels will be an important goal for future research.”

Professor Baron-Cohen commented: “Although these very clear sex differences in brain structure may reflect an environmental or social factor, from other studies we know that biological influences are also important, including prenatal sex steroid hormones (such as foetal testosterone) as well as sex chromosome effects. Such influences need to be teased out, one by one.”

Dr Meng-Chuan Lai, another member of the team, noted: “The advantage of conducting a meta-analysis is that we can summarise the best knowledge from a vast, heterogeneous literature, with a very large sample size. However, we found a bias in the existing literature towards the use of volunteers over 18 years old, probably because this is the easiest age group to recruit and to brain scan. We need more research exploring brain development over the entire lifespan, especially in the early, formative years”.

This study was supported by the Medical Research Council, the Wellcome Trust, the Autism Research Trust, the Dr Hendrik Müller Vaderlandsch Fonds, the Carolus Magnus Fonds under the Prins Bernard Cultuurfonds, and the Waterloo Foundation. It was conducted in association with the NIHR CLAHRC for Cambridgeshire and Peterborough NHS Foundation Trust.

- See more at: http://www.cam.ac.uk/research/news/males-and-females-differ-in-specific-brain-structures#sthash.0Gn3QE4N.dpuf)

Kentucky Fried Brain

I threw it down onto my tray immediately. It looked like a brain.

The Health Risks Of Being Left-Handed

my bias,,, I'm left handed. Some of these attributes declared in the article are common sense. A left handed person is likely to come from a high IQ mother... and that mother may be less willing to be a breader in society, therefor more likely to have a late pregnancy in a culture that is hostile towards childbirth like Sweden.

(Getty Images)

President Obama
(obviously intelligence has nothing to do with how favorable a leader is to it's constituents)

•(WSJ) Left-handed people make up about 10% of the population, while 1% of the population appear not to be dominant with either hand, known as mixed-handed.
•Being left-handed is only partially genetic.
For reasons not clearly understood, handedness depends mainly on how a baby's brain develops while in the womb.
• On average there is no difference in intelligence between right-and left-handed people. But lefties do better on an element of creativity known as divergent thinking.
•Six of the last 12 U.S. presidents, including Barack Obama and George H. W. Bush, have been lefties.
• Left-handed people earn on average 10% lower salaries than righties, according to a recent study. Findings of some earlier studies on income have been mixed.
•Despite popular misperceptions, lefties aren't more accident prone than right-handed people and don't tend to die at a younger age.
•Left-handedness has been linked to increased risk of certain neurodevelopmental disorders like schizophrenia and ADHD. Mixed-handedness is even more strongly associated with ADHD.
•Most people's brains have a dominant side. More symmetrical brains of mixed-handed people may explain the link to some neural disorders.

Left-handers have been the subject of curiosity, stigma and even fear over the centuries. Researchers now, however, are recognizing the scientific importance of understanding why people use one hand or the other to write, eat or toss a ball.

Handedness, as the dominance of one hand over the other is called, provides a window into the way our brains are wired, experts say. And it may help shed light on disorders related to brain development, like dyslexia, schizophrenia and attention deficit hyperactivity disorder, or ADHD, which are more common in left-handed people.
Other recent research suggests that mixed-handedness—using different hands for daily tasks and not having a dominant one—may be even more strongly linked than left-handedness to ADHD and possibly other conditions.
About 10% of people are left-handed, according to expert estimates. Another 1% of the population is mixed-handed. What causes people not to favor their right hand is only partly due to genetics—even identical twins, who have 100% of the same genes, don't always share handedness.
More important, researchers say, are environmental factors—especially stress—in the womb. Babies born to older mothers or at a lower birth weight are more likely to be lefties, for example. And mothers who were exposed to unusually high levels of stress during pregnancy are more likely to give birth to a left-handed child. A review of research, published in 2009 in the journal Neuropsychologia, estimated that about 25% of the variability in handedness is due to genetics.
On average there is no significant difference in IQ between righties and lefties, studies show, belying popular perceptions. There is some evidence that lefties are better at divergent thinking, or starting from existing knowledge to develop new concepts, which is considered an element of creativity. And left-handed people have salaries that on average are about 10% lower than righties, according to recent research performed at Harvard University that analyzed large income data bases, although findings of some earlier studies were mixed.
Left-handedness appears to be associated with a greater risk for a number of psychiatric and developmental disorders. While lefties make up about 10% of the overall population, about 20% of people with schizophrenia are lefties, for example. Links between left-handedness and dyslexia, ADHD and some mood disorders have also been reported in research studies.

Agence France Presse/Getty Images

Lefties have an advantage
in sports such as tennis,
fencing and baseball,
when up against
a righthanded competitor,
but not in noninteractive
sports such as gymnastics.

The reasons for this aren't clear. Scientists speculate it could be related to a concept known as brain lateralization. The brain has two halves. Each performs primarily separate, specialized functions, such as language processing, which mainly takes place in the left hemisphere. There is lots of communication between the hemispheres.
Typically in right-handers, the brain's left side is dominant. But this tendency doesn't hold up with lefties, as scientists previously believed. Some 70% of lefties rely on the left hemisphere for their language centers, a key brain function, says Metten Somers, a psychiatrist and researcher who studies brain lateralization at Utrecht University Medical Center in the Netherlands. This doesn't appear to present problems, scientists say.
The other 30% of lefties appear to exhibit either a right-dominant or distributed pattern, Dr. Somers says. They may be more prone to impaired learning or functioning, and at greater risk for brain disorders, he says.
Hemisphere dominance is typical and more efficient. Symmetry, in which neither side is dominant, is believed linked to disorders, researchers say. People with schizophrenia, for instance, exhibit more symmetrical activation of their brain hemispheres than those without the disorder, studies show.
In a 2008 study, Alina Rodriguez, a psychology professor at Mid Sweden University in Östersund who studies handedness, brain development and ADHD, found that left- or mixed-handedness in children was linked to a greater risk of difficulty with language as well as ADHD symptoms. In another study published last year in Pediatrics, involving nearly 8,000 Finnish children, Dr. Rodriguez found that mixed-handedness rather than left-handedness was linked to ADHD symptoms.
And knowing that a child was mixed-handed and had ADHD symptoms at age 8 helped predict much more accurately than just knowing they had symptoms at that age whether the child would continue to have symptoms at age 16. (What happens when people are forced to switch from writing with their dominant hand to the other isn't well known, experts say.)
One reason that not more is known about lefties is that many studies of how the brain works prohibit left-handers from participating because their brain wiring is known to be different, says Robin Nusslock, a psychology professor at Northwestern University in Evanston, Ill., who uses neuroimaging to study mood disorders.
A potential pathway between prenatal stress and brain wiring could be cortisol, the body's main stress hormone, which can interfere with brain development, says Carsten Obel, a professor at the public-health department at Aarhus University in Denmark who has conducted research on the prenatal environment and risk of disease. Cortisol is able to pass over the placenta barrier to influence the baby.
Several studies show that stressful life events, such as the death of a loved one or job loss, during pregnancy increase the risk of having non-right-handed children. In one study of 834 Danish mothers and their 3-year-old children, Dr. Obel and his colleagues found that mothers who reported multiple stressful events during their third trimester of pregnancy and experienced distress were more than three times as likely to have a mixed-handed child, 17% compared with 5%, according to the 2003 paper published in Developmental Medicine & Child Neurology.
Another large study followed 1,700 Swedish mothers and children until the kids were 5 years old. It found that mothers with depressive symptoms or who underwent stressful life events while pregnant were more likely to have left- or mixed-handed children. The work was published by Dr. Rodriguez and her colleagues in 2008 in the Journal of Child Psychology and Psychiatry.
Experts suggest that left- and mixed-handedness could be used as a risk factor for possible psychiatric or developmental conditions, along with behavioral difficulties, such as having a hard time in school. The presence of such risk factors could prompt early evaluation for those conditions, they say.