Language is such a complex system, which isn’t fully understood. It is said to be universal and unique to all humans. Scientists of all backgrounds have studied to find how we process, interpret, and produce language. The answer is almost never clear, but our understanding of the brain and its systems has developed in recent years.

How did language evolve?

There are many theories about how language evolved: The Vocal Theory suggests it was a natural evolution from primates’ instinctual sounds, which happened due to change in the size of the brain, and structure of the larynx and mouth. The Gestural Theory proposes that, as humans evolved to walk on their feet – freeing up their hands for gesturing – they evolved to speak, so as to free their hands for using tools and doing other tasks. Whatever the case may be, the intricate systems of the brain which allow for all this to happen have fascinated linguists for centuries.

Is language localized to one side of the brain?

The Wada Test (named after Japanese neurologist Juhn Atsushi Wada) helps determine this. Barbiturate (a common anesthetic) is injected into the neck or head on one side to put half of the brain to sleep. Scientists can then test what people can/can’t do while that part of the brain isn’t functioning. For the majority of people, language is processed by their dominant hemisphere. So, for right-handed people, this is the left hemisphere.

However, it’s not that simple (it never is): people can’t be characterized in a binary fashion, as language ability isn’t exclusively controlled by one side of the brain or the other. This system would exclude people whose language functions are generally bilateral: they use both sides of the brain substantially.

A study by Byron Bernal and Alfredo Ardila, where they performed 1,799 Wada tests (mostly on epilepsy patients prior to surgery), found that 10% of right-handers and 27% of left-handers (and ambidextrous) showed evidence that both hemispheres supported their language function. In some patients, shutting down one part of the brain didn’t impair their language at all. Although, shutting down the other part created some interference. In others, shutting down either hemisphere only partially impaired their language. Finally, some were completely unable to produce/understand language when one side was shut down, and when the other one was, it had a partial adverse effect.

This pattern occurred because there are various ways in which the brain can share language functions. In some people, all functions are shared between the right and left brain. In others, only some sub-functions are. Also, some steps towards language processing are shared sequentially between the hemispheres: one step is performed on one side, and the next one on the other side.

While it is important to be cautious when performing studies on patients and then applying the results to healthy people (as it’s possible the epileptic patients’ brains changed to adapt to disease), this study showed how complex the brain’s systems are. Additionally, it showed that only saying ‘most people use their left hemisphere for language functions’ is an oversimplification. Bernal and Ardila write, “It is a frequent understanding that language lateralization is a matter of all or nothing. However, language dominance is mostly a matter of hemispheric advantage for a specific multi-modular cognitive function: language. As such, language in a strict sense is up to a certain point a bilateral brain function.”

How does the brain process, interpret, and produce language?

The fundamentals of interpreting language begin before you are even born. Studies have shown that fetuses can differentiate between female and male voices.

Processing language starts at the auditory cortex, which we use to hear. Many brain regions used to hear sounds are also used to interpret speech. Recent neuroimaging studies have led researchers to propose that language information gets split into a ‘dual stream model’. Information is sent along the dorsal pathway (the ‘speech’ part of the system) to brain regions in both hemispheres. This helps us translate speech input and allows us to reproduce the same speech patterns. The ventral stream (the ‘what’ pathway) passes information along the dominant hemisphere. This allows us to identify the content of speech and understand what it means. 

There are two speech centers in the brain: 

  1. Broca’s area (discovered by Paul Broca, a French physician), in the left frontal cortex: it controls language production.  
  2. Wernicke’s area (discovered by Carl Wernicke, a German neurologist), in the posterior temporal lobe: it analyzes the words heard, and places them in the correct order before you speak. 

To summarize, here is the process from start to finish: when we hear language, the message travels through the ear. The electrical impulse from the vibration enters the primary auditory cortex, which discerns that the sounds came from a human voice. The information then travels to Wernicke’s area to be interpreted, and after to Broca’s area to formulate a response. That message is then transmitted to the primary motor cortex, which signalizes to your larynx and mouth to vocalize the response.  

A screenshot of a cell phone

Description automatically generated
Image: Shows functional areas of the human brain. Dashed areas shown are typically left hemisphere dominant.

What are the effects of brain injury on language?

When Broca’s area is injured, patients know what they want to say, but can’t find the words to express it. This is called expressive aphasia. 

When Wernicke’s area is damaged, the patient has trouble understanding language. They have no problems producing it, but they use grammatical sentences that don’t make any sense. This is called fluent aphasia. 

Some final thoughts

This is an oversimplification of the brain’s many complexities (if it wasn’t, this would have been much longer and way more confusing), and there is still so much yet to be discovered about the human brain. But, hopefully you learnt a bit about how you are able to understand and communicate with those around you. Also, congratulations! It seems you’re keeping up with educational reading, even during this strange summer quarantine: well done!

 Credits: The Neuroscience of Language: https://www.youtube.com/watch?v=Ev_oKHWT_qk, How Humans Process Language: https://animals.howstuffworks.com/mammals/chimps-learn-language1.htm, Language Localization: https://digest.bps.org.uk/2013/11/19/where-is-language-located-in-the-brain-there-are-two-sides-to-this-story/, Bilateral Representation of Language (Bernal and Ardila, 2013): https://www.sciencedirect.com/science/article/abs/pii/S0911604413000602?via%3Dihub, Image Source: http://www.sci-news.com/othersciences/linguistics/language-ancient-general-purpose-brain-circuits-05677.html

This article was written by Sofia Pereira a new contributor and soon to be writer

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