Gender development

Relationship to Brain Lateralisation

Lateralisation: Where a function (e.g., language) is limited to one hemisphere. What is lateralisation? The brain has certain structures and functions. Its structures include such things as hemispheres and lobes. It functions are the jobs it does (e.g.,language, processing visual input and so on). The brain has two hemispheres The two hemispheres can both do similar functions but sometimes the hemispheres differ in their functions. When a function is specialised in one hemisphere, it is called lateralisation (see glossary). The hemisphere that does a function the most is the ‘dominant hemisphere’ (cerebral dominance). Lateralisation is also known as hemispheric asymmetry.

Brain lateralisation Brain lateralisation refers to the uneven distribution of tasks carried out by the hemispheres.  LateralLateral means side.  Any function, e.g. language, which is found on one side of the brain is called a lateralised lateralised functionfunction.The brain is made up of two hemispheres that appear to be symmetrical.  However it is known that each hemisphere is responsible for different functions. 

Which hemisphere is dominant?

Which side of the brain is directing this action?

Which side of the brain is working

out this puzzle?

Which side of the brain

is processing the phone

conversation?

Previously we learned that the development of the embryonic brain can be affected by the presence or absence of hormones in the womb. This may lead to brain lateralisationbrain lateralisation. 

It is believed that male brains are more lateralised male brains are more lateralised with specific functions being allocated to each hemisphere e.g. spatial skills in the right and language skills in the left. 

Functional differences may result from this including increased ability to manipulate objects in space. 

In evolutionary terms this would make males better hunters.

Female brains are less lateralisedFemale brains are less lateralised; their brains have a thicker connective band (corpus callosum) between the hemispheres.  This means they use both sides for they use both sides for language and therefore have better language and therefore have better communication skillscommunication skills.  In evolutionary terms this would make females better at socialising and therefore binding social groups together.

In malesmales, there is more leftleft hemisphere activity during linguistic tasks, but in femalesfemales there is usually bilateral brain activity bilateral brain activity during the same tasks. 

During spatial tasks, malesmales show high levels of activity in the rightright hemisphere; whilst in femalesfemales we are again more likely to see bilateral brain activitybilateral brain activity. 

Studies show that the corpus callosum is thicker in corpus callosum is thicker in females females and perhaps this explains why female brains are more bilateral, because the two hemispheres communicate more efficiently.

Test your Brain Sex

You can do this by logging on to the following link and completing the test

http://www.bbc.co.uk/science/humanbody/sex/index_cookie.shtml

Have a go, you may be surprised by what you find out!

Sex differences in Brain Maturation during childhood and adolescenceDe Bellis et al, 2001

Aims

1. To investigate three areas of the brain three areas of the brain to find out if the volume of those areas changed over time from childhood to adolescence

2. To investigate whether there were differences in male and female brains

ProcedureMRI Scanner

Magnetic Resonance Imaging (MRI)

Can Can you you recall recall how how the MRI the MRI scan scan works?works?

(LINK) MAGNETIC RESONANCE IMAGING(MRI)

Put another way

MRI detects signals produced by displaced radio waves in a magnetic field.

It provides a detailed anatomical view of the

brain.

MRI scanning uses a strong magnetic field which affects some atoms.

ProtonsProtons (positively charged particles) in hydrogen atoms in water behave like compass needles.

The scanner’s electromagnet causes the protons to ‘point’ in the same direction.

When radio waves are passed through the head the protons return to their original positions and this is detected by the scanner.

Parts of the brain with more hydrogen atoms appear paler; those with fewer hydrogen atoms look darker.

ProcedureProcedure Experimental method: cross sectional / lab-

based The participants were healthy children and

adolescents 61 males and 57 females Age range 6 to 17 years They advertised for Ppts in the local community Ppts underwent clinical evaluations to ensure no

one had any mental disorders

ProcedureProcedure

There was no significant difference no significant difference in the groups in terms of:

Ethnicity Socioeconomic status Handedness IQ

ProcedureProcedure The majority of ppts showed above

average IQ Males were significantly taller than

females Fully informed consent was obtained from

both the ppts and their parents Ppts received money for taking part

QuestionsWhat type of sampling method did De Bellis et al use?

1.Opportunity

2.Self-selected

3.Random

4.Stratified

Answer

Self selectedSelf selected

QuestionsQu: Which items were there found to be no

differences between the pps? Answers Ethnicity, Socioeconomic status, Ethnicity, Socioeconomic status,

Handedness and IQHandedness and IQ

Qu: What difference was there between the groups?

Answer HeightHeight

ProcedureProcedure

Prior to being scanned, pps underwent a desensitisation procedure in a simulation scanner – this reproduced the sights and sounds of the actual MRI to get pps used to the environment

This meant they were more co-operative during the actual scan and led to an improvement in image acquisition

ProcedureProcedure During the actual MRI scan ppts were able

to watch videos of their favourite films Ppts were motivated to remain still by being

allowed to see the images of their brain after scanning (if they moved they’d be blurry)

No sedation was used!!! Scanning was supervised by a

child/adolescent psychiatrist

Procedure

The brain scans were read by people who did not know whether the scan was from a boy or a girl

Question: Why was this important?

Questions Which ethical procedures did De Bellis et

al follow? Answers: fully informed consent was obtained from fully informed consent was obtained from

both Pps and their parentsboth Pps and their parents Procedures were put in place to ensure Procedures were put in place to ensure

minimal discomfort/distress during the minimal discomfort/distress during the procedure i.e. being able to watch favourite procedure i.e. being able to watch favourite film, not sedated, Child psychiatrist present - film, not sedated, Child psychiatrist present - competencecompetence

ResultsResults – note they found correlationscorrelations

Scattergrams

of cerebral volume

solid lines =

males

dotted lines =

Female

Results

The older the ppts the less grey matter they had – especially males

White matter and the corpus callosum both increased with age, more so for the boys

ConclusionsConclusionsThey concluded that boys had faster changes than females as they aged

They also said that the differences in the male and female brain could explain why males and females have different cognitive abilities

One of these reasons could be linked to hormones. One of these reasons could be linked to hormones. Oestrogen delays pruning. Oestrogen delays pruning. Testosterone promotes Testosterone promotes myelination. myelination.

QuestionsQuestions

What method did they use to analyse the data?

Answer: CorrelationCorrelation Males showed faster changes than

females True/false? Answer: TrueTrue

1. With age the volume of grey matter decreased .

2. The corpus callosum and white matter volume increased.

3. It was at different rates for males & females

What was found?

Gender Increase in White Matter Increase in Grey Matter

Increase in Corpus Callosum

Male Increased by 45.1% Reduced by 19.1%

58.5% increase

Female Increased by 17.1% Reduced by just 4.7%

27.4% increase

The aim of this study was to look at differences in the function of the brain, based on different genders and ages.

An MRI scan was used to observe white and grey matter volume over a period of time. 118 participants. 61 males and 57 females were used.

Participants were children and adolescents, they were defined as healthy after undergoing medical checks for mental disorders.

Volunteer sample (paper advert).

Informed consent from each parent was obtained in writing.

Before the experiment happened there was a trial run to practice. It consisted of a machine which replicated an MRI scanner . This was to enable the participants to understand what would happen in the real experiment. Furthermore it was hoped that it would train the participants to keep their head still.

Participants were told in the experiment that images of their own brain would be shown to them at the end, however if they didn’t stay still the images would be blurred.

Trained researchers using computer software looked at the results of each brain scan.

Describe – include sufficient detailinclude sufficient detail

✓The participants were protected against psychological and physical harm because a professional neuroradiologist was in charge of each MRI scan, a psychiatrist also remained with the child or adolescent throughout.

✓ Reliability would be high because of the fact that participants kept their heads still so the images were clear and precise.

✓ validity is high because controls were in place e.g similar IQ X Low in generalisability as the participants were all of similar IQ scoring

(at least 116) which may give different results to someone of lower IQ. X It’s possible that reliability and validity may be decreased due to

difficulty of measuring white and grey matter X The study was cross-sectional instead of longitudinal which means

that results could be increased significantly in reliability as participant variables would be identified and the change during growing up in both genders could be found and noted.

Evaluation