1. Dept. of Brain & Cognitive Sciences
Language and the brain
Rajeev Raizada
Dept. of Brain & Cognitive Sciences
raizadalab.org

2. Language and the brain: why bother with brain stuff in the first place?
Key language areas, and lesion deficits
Lots of interactive brain areas
It’s not just a couple of areas on the left
Interpreting brain activation:
Who cares which bit of the brain lights up?
We want brain imaging to tell us about linguistic information processing, or linguistic representations

3. Language areas in the brain
Some brain areas are specialised for language
Broca's area: speech production
Wernicke's area: speech perception
On the left side of the brain (in 95% of people)
This is pretty much the only left-brain / right-brain saying that is actually true
What does "specialised for language" actually mean?
If you lose these areas, you lose language
When you use language, you use those areas
BUT: That does not mean that they only do language
E.g. Broca's area may be involved in music perception

4. Broca's area: crucial for speech production
Paul Broca (1861): patient "Tan"
Severe deficit in speech production: could only say "tan"
Good language comprehension
Tan's brain: lesion (injury) in left frontal cortex

5. Auditory cortex and Wernicke's area
Auditory cortex: all sounds pass into here
Mostly specialised for low-level features, e.g. raw frequency
Bilateral (on both left and right sides of the brain)
Wernicke's area (Carl Wernicke, 1874)
Patient with very poor speech comprehension
Good speech production
Lesion on left side, just behind auditory cortex
Specialised for processing "higher level" sounds: speech

6. Auditory cortex and Wernicke's area
From

7. Language areas in the brain
From University of Washington's Digital Anatomist project

8. An example of Broca's aphasia in the news: Gabby Giffords
Start at 2mins

9. Wernicke's aphasia Deficit of comprehension, not production.
Fluent speech, but lacking coherent meaning

10. There's more to language in the brain than just Broca's and Wernicke's
Friederici, A. D. (2012). The cortical language circuit: from auditory perception to sentence comprehension. Trends in cognitive sciences, 16(5),

11. The claim "language is on the left" is a total over-simplification
Specht, K. (2013). Mapping a lateralization gradient within the ventral stream for auditory speech perception. Frontiers in human neuroscience, 7.

12. The claim "language is on the left" is a total over-simplification
Peelle, J. E. (2012). The hemispheric lateralization of speech processing depends on what "speech" is: a hierarchical perspective. Frontiers in human neuroscience, 6.

13. What does brain imaging do, and what can it tell us?
And what does it not tell us?

14. Problem: This picture does not show any neural mechanisms

15. MRI Magnetic Resonance Imaging
Takes a 3D picture of the inside of body, completely non-invasively
One picture, just shows the structure

16. fMRI functional Magnetic Resonance Imaging
Shows brain activity (indirectly)
Takes a series of pictures over time, e.g. one every three seconds
The “f” in fMRI means functional, i.e. you get a movie of brain function, not a still image of brain structure

17. What are we actually measuring with fMRI?
An MRI machine is just a big magnet (30,000 times stronger than Earth's magnetic field)
The only things it can measure are changes in the magnetic properties of things inside the magnet: in this case, your head
When neurons are active, they make electrical activity, which in turns creates tiny magnetic fields
BUT far too small for MRI to measure (100 million times smaller than Earth's magnetic field)
So, how can we measure neural activity with MRI?

18. What makes fMRI possible: Don't measure neurons, measure blood
Two lucky facts make fMRI possible
When neurons in a brain area become active, extra oxygen-containing blood gets pumped to that area. Active cells need oxygen.
Oxygenated blood has different magnetic properties than de-oxygenated blood. Oxygenated blood gives a bigger MRI signal
End result: neurons fire => MRI signal goes up
This fMRI method is known as BOLD imaging: Blood-Oxygenation Level Dependent imaging. Invented in 1992.

19. But neurons do the real work, not blood
But neurons do the real work, not blood. Neurons represent and process information
Individual nerve cells (neurons) represent information
Sensitive to “preferred stimuli”, e.g. /ba/
These stimuli make them active
Firing activity: send electrical spikes to other neurons
/ba/
/ba/-sensitive neuron

20. Populations of neurons process information together
Information is distributed across large populations of neurons, and across brain areas
There's no “grandmother cell”: the one single cell that recognizes your grandmother
To really understand the brain, we'd need somehow to read the information from millions of individual neurons at once!

21. The basic design of an fMRI experiment
Aim:
Find which brain areas are active during a given task
E.g. discriminating speech sounds, producing speech
Typical design:
Present blocks, e.g. 30s of task, 30s of rest
Measure fMRI activity regularly every few seconds
Look for brain areas which are more active during the task periods, compared to rest periods

22. Example time-courses TIME Time-course of task versus rest periods Task
MRI signal from voxel that correlates well with task: Active
Signal from voxel that does NOT correlate with task: Inactive
TIME

23. What are those little coloured blobs, actually?
Colour represents statistical significance of how well the voxel's activation correlates with the task.
The hi-res grayscale anatomical picture underneath the coloured blobs is a completely different type of image, from a different type of scan. Shows the anatomy at the spot where the significant voxel's time- course was recorded.

24. The key problem
Interpreting what brain activation means

25. Reverse inference Why it's hard to infer processing from activation: Brain areas are multi-functional
???
Attention
Intention
Spatial reasoning
Numerical magnitude
Parietal cortex

26. A famously horrible example
“You love your iPhone, literally”
“But most striking of all was the flurry of activation in the insular cortex of the brain, which is associated with feelings of love and compassion. The subjects' brains responded to the sound of their phones as they would respond to the presence or proximity of a girlfriend, boyfriend or family member.
In short, the subjects didn't demonstrate the classic brain-based signs of addiction. Instead, they loved their iPhones.”

27. An example of reverse inference from everyday life
If you have Ebola, you will start off by having flu like symptoms
“I am having flu like symptoms”
“Oh no! I must have Ebola!”

28. Interpreting brain activation
Who cares which bit of the brain lights up? We want brain imaging to tell us about linguistic information processing, or linguistic representations Example study: Does a person’s brain have well-structured representations for performing a given language task?

29. Well-structured representations for doing a task, versus poorly-structured
Weight
Height
Sumo wrestlers
Basketball
players
Faculty
Students
Wanted:
One single task, one set of stimuli
BUT: Some people can do task, other people cannot

30. Different languages carve up acoustic space differently: /ra/ and /la/ in English and Japanese speakers
Raizada et al., Cerebral Cortex (2010)

31. Formants and perceptual discriminability
Raizada et al.,
Cerebral Cortex (2010)

32. Prediction: fMRI patterns for /ra/ and /la/ are more separable in the brains of English speakers than in Japanese speakers
English speakers:
Can perceive /r/-l/ distinction
fMRI patterns are separable
Japanese speakers:
Cannot perceive /r/-l/ distinction
fMRI patterns are not separable
/ra/
/ra/
/ra/
/la/
/la/
/ra/
/la/
/la/
/ra/
/la/
/ra/
/ra/
/la/
/ra/
/ra/
/ra/
/la/
/la/
/la/
/la/
/la/
/ra/
/ra/
/ra/
/ra/
/la/
/ra/
/ra/
/la/
/la/
/la/
/la/

33. Will neural pattern separability match perceptual discriminability?
Predicted pattern-separability, if it matches perception:
English: F3-difference > F2-difference
Japanese: F3-difference = F2-difference
fMRI pattern separability contrast:
F3-separability minus F2-separability
Is this neural difference greater for English than Japanese?
Key point: the classifier doesn't get told anything about people's behaviour, or about who is English or Japanese

34. Individual differences: Neural pattern separability predicts behavioural performance
Raizada et al., Cerebral Cortex (2010)
Just as people try to look for properties that are true of all languages, we want to find regularities that are true of all people's brains in the way they represent language
Correlation after partialling out effects of group membership: r = 0.389, p < 0.05

35. Summary The brain is astonishingly good at processing language
Nobody understands how it achieves this
But we do have some exciting leads
Lots of brain areas, all representing multiple types of information, all communicating with each other
Not just Broca’s and Wernicke’s areas
Not just in the left hemisphere
Challenges for neuroscience
What information processing tricks does the brain use?
What representations does it use, how does it use them?