What is Brain lateralization?

In this blog we will discuss what Brain lateralization is 

We will also briefly explore how brain lateralisation impacts brain function and the accuracy of the theory of brain lateralisation. 

What is Brain lateralization?

Brain lateralisation refers to the theoretical view that the functions of the brain such as perception, cognition, processing, memory etc are performed by separate and distinct regions of the brain. 

It is based on the idea that functions like language memories, motor movements etc are controlled by different areas of the brain and this theory goes against the holistic theory of the brain which is the theory that all parts of the brain are involved in the processing of thought and action.

The human brain, in terms of structure, is divided into two hemispheres- left and right- and the two sides are joined together by the corpus callosum, a bundle of nerve fibres which is located in the middle of the brain.

These structures in the brain are contralateral, meaning that each hemisphere controls the opposite side of the body so the right hemisphere controls the muscle movements of the left arm and leg.

Brian Hemispheric lateralization is the idea that each hemisphere is responsible for different functions that are localised to either the right or left side. For example, the theory believes that the left brain deals with language functions, such as formulating grammar and vocabulary whereas the right side of the brain deals with visualisation and perception. 

Does brain lateralisation occur naturally?

When we consider how brain lateralisation occurs and whether one is born with a lateralized brain or not, we can look into the issue of language processing of the brain. 

Early research in brain imaging found that when participants underwent fMRI, people were observed to exhibit higher levels of activation- nerve firing- in the right side of the brain indicating that they had language dominance that is typical in the human populace. 

Researchers began to look into the question as to whether lateralization of language function is something that occurs from birth, or if this lateralization develops over time.

In a recent study by Olulade et al. (2020)  that reviewed the neural basis of language development, researchers compared the fMRI scans of adults and children on language based tasks and the results found that in the youngest of children (aged 4-6 years old), there were left and right hemispheric activation- indicating that language was not lateralized to one hemisphere for younger children.

Where as for the adults and older adults, the activation was mostly on the left side with significantly decreased right-side activation of the brain in terms of language for over 60% of the adults which suggested that lateralization of the brain in terms of language was not innate rather that lateralization of language to the left hemisphere, develops over time as a person ages. 

A review of prior research done on the lateralization of the brain in terms of the processing of the brain found that both the and right hemispheres have different functions regarding emotions.

Research has found that the right hemisphere is better at controlling emotional expressions and recognising emotions in other people whereas the left side of the brain tend to deal with negative emotions which implied that both side of the brains had different functions related to one aspect of human experiences and that a certain function is not just limited to one side of the brain. 

Is brain lateralisation the same for men and women?

There has been several studies that has found that brain lateralisation functions for men and women are different. 

For example, a 2012 study that aimed to study the patterns of lateralization connectivity and the gender effects on these laterality patterns of the human brain found that there appears to be differences in lateralisation function. 

The study was conducted on 913 healthy participants with the process of parallel computing where short and long range connectivity densities were quantified. 

The researchers found that the right lateralization of connectivity in various of the brain such as the temporal, frontal, and occipital cortices were increased quantitatively whereas for women the lateralization of connectivity were more on the left side of the frontal cortex. 

This study suggested that there are some differences in the lateralisation of the brain in males and female brains which could explain the differences in cognitive styles between men and women. 

For example, because of these differences, it is possible that women will have linguistic advantage over men because their brain is more lateralized in connectivity in the left side while the men will have more advantage over women in terms of visual functions due to the increased lateralisation in the right side of the brain. 

Another study that supports this finding is the review of studies in terms of the differences of brain and brain functioning between males and females.

The researchers examined indidvdiuals who have experienced brain injury to the area of the ventral-medial prefrontal cortex (vmPFC) that is associated with decision-making and emotion and found that there appears to be sex realted differences. 

The review found that people who have brain damage to their right vmPFC tend to exhibit deficits in terms of emotional, and decision-making processes at a higher extent than women that were part of the study. 

How accurate is the theory of brain lateralization?

The theory of brain lateralisation can be traced back to the work of Roger W Sperry who has studied brain functioning of people with split brain procedures where the corpus callosum has been severed to treat a form of epilepsy. 

Sperry observed that people who have had this procedure seemed to exhibit a certain kind of behaviour and cognitive processes where even if they were unable to name objects processed by their right side they were able to recall names of objects processed by the left. 

Based on this observation, Sperry suggested that language was controlled by the left side of the brain as a result of which gave the idea of brain lateralisation- that the two hemispheres of the brain have two separate functions.

It was believed that the right side of the brain is associated with:

  • Recognizing faces
  • Expressing emotions
  • Creating music
  • Reading emotions
  • Appreciating color
  • Using imagination
  • Being intuitive
  • Being creative

Where as the Left Brain is associated with 

  • Language
  • Logic
  • Critical thinking
  • Numbers
  • Reasoning

However, research today has found that the functioning of the brain is not as dichotomous as once believed and rather the functioning of the brain is stronger when both hemispheres work together. 

Now, the understanding is that the two sides of the brain collaborate together and it is by collaboration and working together that the brain is able to do a broad variety of tasks which is not as efficiently possible if only one side of the brain does it. 

For example, Sperry believed that the left side of the brain is what monopolises language processing, however more recent research has found that the right side of the brain also works to process the emotional features of language such as rhythms and tone. 

Researchers now agree that people don’t tend to dominate the left side or right side and rather manifestations of dominance such as handedness is due to the neural pathways and connections that are unique to each individual. 

Even though science and research today has demonstrated that this brain lateralisation of the left and right brain theory is a myth, it is still widely believed since most people are unaware of how outdated this theory is. 

Conclusion

In this blog we have discussed what Brain lateralization is 

We will briefly explore how brain lateralisation impacts brain function and the accuracy of the theory of brain lateralisation. 

FAQ related to Brain Lateralization

What is an example of brain lateralization?

Brain lateralisation refers to the theoretical view that the functions of the brain such as perception, cognition, processing, memory etc are performed by separate and distinct regions of the brain. 

For example, recent research has found that the right side of the brain also works to process the emotional features of language such as rhythms and tone. 

What are some examples of lateralization?

Brain lateralisation refers to the theoretical view that the functions of the brain such as perception, cognition, processing, memory etc are performed by separate and distinct regions of the brain. 

For example, the left side of the brain is believed to be associated with emotions where as the right side with decision making. 

What is the importance of brain lateralization?

Brain lateralisation is important because researchers studying the human brain believe that  having a lateralized brain increases brain capacity.

This belief developed because having a lateralized brain means that neural circuits do not have to be duplicated in each hemisphere so that each can have its own specialised circuits and functions.

Can you have half your brain removed?

Yes, you can have half your brain removed and still live however, a hemispherectomy is a rare surgery.

In this surgical procedure half of the brain is either removed or disconnected from the other half, usually done on children and adults who have seizures and do not respond to pharmacological treatments, usually as a last resort. 

How do you test brain lateralization?

Brain lateralization can be tested and examined with imaging by comparing and observing brain activation of the right or left brain during a specific task for example language tasks or visual tasks and recording them with methods like PET scans, fMRI scans, or EEG recordings.

References

Guy-Evans, O. (2021, May 18). Lateralization of brain function. Simply Psychology. www.simplypsychology.org/brain-lateralization.html

Lateralization. Good therapy. Retrieved on 21st March 2022. https://www.goodtherapy.org/blog/psychpedia/lateralization

Cherry. K. Left Brain vs. Right Brain Dominance. Verywellmind. Retrieved on 21st March 2022. https://www.verywellmind.com/left-brain-vs-right-brain-2795005#toc-research

Olulade, O. A., Seydell-Greenwald, A., Chambers, C. E., Turkeltaub, P. E., Dromerick, A. W., Berl, M. M., Gaillard, W. D., & Newport, E. L. (2020). The neural basis of language development: Changes in lateralization over age. Proceedings of the National Academy of Sciences of the United States of America, 117(38), 23477–23483. https://doi.org/10.1073/pnas.1905590117

Silberman, E. K., & Weingartner, H. (1986). Hemispheric lateralization of functions related to emotion. Brain and Cognition, 5(3), 322–353. https://doi.org/10.1016/0278-2626(86)90035-7

Tomasi D, Volkow ND. Laterality patterns of brain functional connectivity: gender effects. Cereb Cortex. 2012 Jun;22(6):1455-62. doi: 10.1093/cercor/bhr230. Epub 2011 Aug 30. PMID: 21878483; PMCID: PMC3450858.

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