Saturday, August 16, 2014

Brain volume is larger for Men than Women, How ?

A new study of thousands of brains from more than 20 years of neuroscience research has revealed the structural differences between male and female brains. 'For the first time we can look across the vast literature and confirm that brain size and structure are different in males and females,' said Amber Ruigrok, who led the study.

The meta-analysis of more than 126 articles published between 1990 and 2013 is the first of its kind to be conducted, and shows that on average male brains have a total volume that is between 8 and 13 percent larger than that of females, took in 218 different studies, covering brains from individuals as young as birth to 80 years old.

The team from Cambridge University, led by doctoral candidate Amber Ruigrok and Professors John Suckling and Simon Baron-Cohen from the Department of Psychiatry, performed a quantitative review of the brain imaging literature testing overall sex differences in total and regional brain volumes, covering all ages from babies to pensioners to reach their conclusions.

“This is the first meta-analysis of sex differences in brain structure and in this study we summarized all the evidence we could find and tried to give an overview of what is known from the current literature,” Ruigrok told The Independent.

Looking more closely, researchers found the differences in volume between the sexes were located in several regions. 

“Certain areas were larger in men, certain areas were larger in women, with a lot of these differences originating from in the limbic system – parts of the brain such as the amygdala and the hippocampus.”  

Professor Suckling noted that “the sex differences in the limbic system ( which deals with emotion, and the language system) include areas often implicated in psychiatric conditions with biased sex ratios such as autism, schizophrenia, and depression.” Professor Suckling said.  

" We should no longer ignore sex in neuroscience research, especially when investigating psychiatric conditions that are more prevalent in either males or females ".  

On average, males also 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).  

Professor Baron-Cohen said: '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.'

“This new study may therefore help us understand not just typical sex differences but also sex-linked psychiatric conditions,” he added.

However, the research does not draw any direct links between brain structure and function, and the team from Cambridge stressed that the difference in volume does not have direct implications for the gender bias in psychiatric conditions.

“Previous research has shown that the prevalence, age of onset, and symptomatology of many neurological and psychiatric conditions also differ between males and females,” said Ruigrok.
Dr Meng-Chuan Lai, another member of the team, called for further research.

'We need more research exploring brain development over the entire lifespan, especially in the early, formative years,' she said.

“Future research should test whether sex differences in brain structure underlies skewed sex ratios of neurological and psychiatric conditions and whether brain differences that characterise such conditions are caused by the development of typical sex differences in the brain." 

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