A Condensed Dissertation on Neurolinguistics and Aphasia

For my dissertation I wrote about Aphasia and language processing in the brain. It is in this post that I will try and shorten a 13,000 word thesis into a 600-word blog post for the 'everyday blog reader' - with all the boring bits (like referencing) taken out. 

Neurolinguistics is the study of how the brain ('neuro') processes language ('linguistics'). While neurologists study the brain and nervous systems, linguists generally study the way human language is structured. It is neurolinguists that have a particular interest in human neurology and the changed relationship between brain and behaviour proceeding damage to the brain - with specific focus on the precise location of brain damage or lesion (damaged brain tissue). I found this entire topic hugely interesting, and I hate to sound a teacher's pet but I LOVED reading up on this for my dissertation. 

First top fact. Instead of language areas in our brain being ordered into activities such as speaking, writing, and listening, it is organised into hearing words, speaking words, seeing words and generating words. Below is a really cool image of brain activity during a PET scan. The patient would have been asked to repeat words, read aloud, form sentences etc. This shows that different functions are controlled by different areas in our 'language centre'.

Second top fact is that no two brains are alike in the precise pattern of gyri and sulci (all the wrinkles and knobbly bits you see on the surface of a brain), although neurologists have identified a series of 'landmarks' common with all human brains. Landmarks refer to particularly large creases or folds in the brain and have long Latin names which I won't bore you with, and refer to the various areas of the brain's surface, names in the diagram below. It's a bit like a big mountain - all the rivers and streams running through it are named, but all the cracks in the dry earth are different and unique.

And a final fact, for all those GCSE psychologists studying Kanzi the talking ape (who only achieved a string of three words); Ever wondered why monkeys - our primates - haven't conquered the ability to speak? The frontal part of our brains are almost double the size of a monkey's, meaning we have enough room for a 'language centre'. Mind=Blown.

This diagram featured A LOT in my dissertation. #Landmarks #Gyri 

In most people, our 'language centre' (like a switch board for various language activities and processes) is in our left hemisphere - about 96% right handed people, and 70% left handed people. My paper focused on the effects of damage or injury to that particular part of the brain. Even with our brain encased in a skull of bone, this is not enough to protect it against impact. There are many ways someone can injure their language centre, or left hemisphere, causing an inability to speak or difficulties in particular language activities. This could be from an accident - a fall down the stairs, a collision, penetration, an attack or blow to the head; or an internal injury including blood clotting, stroke (when blood is unable to reach a part of the brain) or a lesion caused by infection or disease (e.g. meningitis). Resulting problems will vary depending on the extent of damage, and the location of damage. A particular injury might leave the individual exclusively with visual problems, or difficulties in moving particular sets of muscles. I focused on the injuries that leave individuals with language deficits, such as the planning, articulation and fluency of speech, and the various categorisations of aphasia - as not all aphasics (people with aphasia) suffer from the same linguistic and grammatical features. The largest single cause of adult language disorders is stroke, where blood flow to the brain is disrupted by a blood clot or a ruptured blood vessel. 

Much of our knowledge around certain brain areas and their relationship with our language abilities has come from studies of aphasia. Aphasia is the partial or total loss of language abilities following damage to the brain. Interestingly those with aphasia will not have suffered the loss of cognitive faculties or the ability to move the muscles used in speech, suggesting that there is a specific region in the brain used for speech.

The rest of my dissertation is very long and goes down several paths of study (clinical distinctions, plasticity, communication, epilepsy and split-brain patients, various neuro-scanning techniques etc). If you study Aphasia, you’ll learn about two important figures in your first lecture – Paul Broca and Carl Wernicke who provided crucial evidence for the localisation of language function to a specific region within a cortical hemisphere. This means they identified an area in the brain which controlled language by making several observations based on patients with language disorders and their subsequent post-mortem inspections in the late 1800s. It was pretty tricky and time consuming, as they had to asses a patient with communication issues (very slow and laborious speech with difficulty stringing two words together, or in Wernicke’s case, fluent speech that was complete jibber jabber and held absolutely no meaning) and then when they died, slice open their brain and see what area was damaged. They only had 2 or 3 patients each, but it was enough (at the time) to see a correlation between the damaged area and the subsequent language issues.

I really really want to say something about plasticity (I’m 400 words over my ‘limit’ already) as it was this phenomenon that got me interested in neurolinguistics. Neuroplasticity, or 'cortical remapping' is the brain's ability to change or adapt itself through the process of cell reorganisation, axon growth and synapse formation. When you learn a new thing – take playing the piano – your brain creates new pathways, and each time you practise or perform that task these synapses are strengthened. You may have heard of ‘muscle memory’ which is picking up a bike and being able to ride it, without having to remind yourself how to do it. This is because of the repeated practise, and strengthened synapses. There's an incredible paper by Thomas Munte which explains that musicians have a greater level of neuroplasticity and grey matter in their brains than non-musicians. Each fact just gets better and better.

Neuroplasticity, in my opinion, is the future hope for aphasics. Sadly there is a ‘cut off period’ where your brain becomes much slower at learning new things (which is why learning a new language becomes more difficult after age 13), and explains why a child with a trauma to their language centre has a greater chance of re-learning their language skills than a 60 year old. If we can find a way to kick start the process of neuroplasticity again in adults, perhaps this could help them recover particular language abilities. There is also debate over whether the right hemisphere has the ability to take on the language centre if the left is too traumatised (it doesn't, for various reasons).

A final note on hemisphere dominance: don't be fooled by those online tests: 'Right brained? Left brained? Take the test', plastered all over Facebook. Just because you're creative and artistic does not mean you're right hemisphere dominant, and similarly, if you're into maths and have an analytic brain, this does not automatically make you left-hemisphere dominant. Trust me, the way to find out your hemispheric dominance is a lot more complex than 'which colour appeals to you most'.

If somehow I've motivated you enough to read further, then the best book by far to dip your toes into is ‘Language and the Brain’, by L. Obler and K. Gjerlow (1998: Cambridge University Press).