1. Introduction to
Linguistics VI
The imaged brain

2. Limitations of lesion studies
Introduction to
Linguistics
Limitations of lesion studies
• No control over lesion location.
Lesion location depends on vasculature.
• Lesions are typically large -> limited spatial Resolution
• Mapping cortical damage to function leads to focus on one brain
region, rather than on networks
• Individual subject serves as evidence – Variability
• Compensation may be idiosyncratic:
Patient ≠ healthy - x
Patient = healthy - x )y?z?) + abc

3. Mapping Neuroscience Techniques
Introduction to
Linguistics
Mapping Neuroscience Techniques
• Imaging techniques provide a window into the brain processes that occur in a healthy person
• Brain responses at the level of higher cognition can essentially be characterized with respect to time and space.

4. to Methods with high spatial resolution Linguistics Introduction
PET - Positron emission tomography
fMRI – functional Magnetic Resonance Imaging

5. Basic principles of MRI
Introduction to
Linguistics
Basic principles of MRI
Magnetic resonance imaging (MRI) uses strong magnetic fields to create images of biological tissue.
Why do we need a magnet?
The technology is based on
nuclear magnetic resonance (NMR)
A physical phenomenon in which nuclei in a magnetic field absorb and re-emit electromagnetic radiation.

6. Basic principles of MRI
Introduction to
Linguistics
Basic principles of MRI
Atomic nuclei such as hydrogen nuclei (‘‘protons’’) can be influenced by an external magnetic field.

7. Basic principles of MRI
Introduction to
Linguistics
Basic principles of MRI
Stability
If energy is applied to the nuclei at a particular frequency, known as the resonant frequency, some low-energy spins will absorb that energy and change to the high-energy state.
Excitation
After the energy source is removed, some spins will return to the low-energy state by giving off that energy.
Relaxation

8. Basic principles of MRI
Introduction to
Linguistics
Basic principles of MRI
After the energy source is removed, some spins will return to the low-energy state by giving off that energy.
Relaxation
T1 (longitudinal) Relaxation
T2* (transverse) Relaxation
Results from the net magnetization returning to its aligned position
Results from dephasing of the protons
The basis of MRI anatomical signal
The basis of BOLD-fMRI signal

9. Introduction to
Linguistics
MRI Vs. fMRI + T1
T2*
T1 + T2*

10. The basis of functional MRI
Introduction to
Linguistics
The basis of functional MRI
• The breakthrough enabling MRI to be utilized for the examination of
functional aspects of human cognition came about with the discovery of
the so-called ‘‘blood oxygenation level dependent’’ (BOLD) response
• The basic idea behind the BOLD is that, since the brain offers no storage
space for energy, all energy usage must be compensated immediately
• This means that active neural regions must be
provided with energy carriers via the blood flow
• The main carrier of energy in all metabolic cycles is oxygen, which is
transported via the blood by means of hemoglobin
• oxygenated and deoxygenated hemoglobin are associated with different
magnetic properties

11. Introduction to
Linguistics
BOLD fMRI
REST
Activation =

12. to BOLD fMRI Linguistics Introduction
The functional MRI signal is always a contrast between rest and task. This contrast is mainly driven by an increase in oxyhemoglobin, causing protons to precess in phase, which consequently produces a stronger signal as compared to rest.
REST
Activation

13. to The Chain of Events in fMRI Linguistics Introduction Localized
increase in
neuronal activity
Increased
blood flow
to active
region
Cognitive
task
Local vasodilation
(widening of local blood vessels)
Increased
MR signal in
a specific
brain region
Decreased Ratio:

14. Introduction to
Linguistics
The functional images

15. An experimental paradigm
Introduction to
Linguistics
An experimental paradigm

16. to data analysis – voxel by voxel Linguistics Introduction
Stimulus block
Rest
block
Time

17. to Statistical parametric map Linguistics Introduction
Heard sentences vs. Rest
Voxels with
above-threshold
correspondence
level are colored

18. Introduction to
Linguistics
Functional regions in the cortex

19. Introduction to
Linguistics
Single subject results

20. to Interindividual variability Linguistics Introduction
• Kathrine Amunts had shown that
there is a significant interindividual
variability in the cyto-architecture
of cortical areas, far beyond
Brodmann’s classical scheme
• Which means we cannot use
anatomical markers to pinpoint
different functional areas in
individual subjects…
Amunts et al. 2004
Amunts et al. 2004

21. to Functional Localizers Linguistics Introduction
A functional localizer is a short fMRI scan that aims to functionally define the individual’s regions of interest

22. to Why use fMRI ? Linguistics Introduction
• Localization – where in the brain do we process information about ….? – Pattern of activation
• Dissociation – Do we process X and Y using the same brain mechanisms? – Same or different pattern of activation

23. to Advantages of fMRI Linguistics Introduction
• Non-invasive method with no known risks that provides the
best spatial scale in studying the human brain • Repeat measurements within & across subjects • Study brain function \ cognition in an awake behaving human

24. to Disadvantages of fMRI Linguistics Introduction
• Noise • Low temporal resolution • Is not applicable to all populations due to
the need to stay still

25. water is the most convenient molecule to study with diffusion MRI
Introduction to
Linguistics
Diffusion Weighted Imaging (DWI)
Diffusion weighted imaging (DWI) is a form of MR imaging, based upon measuring the random Brownian motion of water molecules within a voxel of tissue
water is the most convenient molecule to study with diffusion MRI
We can use MR to track the diffusion of protons (within water molecules) in a specific direction
This allows us to have some kind of correlate for the motion of the diffusing particles along a particular axis
The intensity of each voxel reflects the best estimate of the rate of water diffusion at that location

26. to Diffusion Weighted Imaging (DWI) Linguistics Introduction
DWI measurements reflect the amount of hindrance/restriction experienced by water molecules moving with a component of displacement along the axis, averaged over the voxel
Diffusion anisotropy in white matter originates from its specific organization in bundles of more or less myelinated axonal fibers running in parallel
Thus, diffusion in the direction of the fibers is faster than in the perpendicular direction.
So it is possible to probe WM architecture using a model that captures both direction and amount of diffusion in each and every voxel
More anisotropic
More isotropic

27. Introduction to
Linguistics
Diffusion Tensor Imaging (DTI)
Directions

28. to Diffusion Tensor Imaging (DTI) Linguistics Introduction
The color assignment is arbitrary, but the typical convention is to have the orientation of the principal eigenvector control hue and fractional anisotropy (FA) control brightness.
FA color map
0 < FA < 1

29. to Tractography Linguistics Introduction Where do these fibers pass?
FA color map
Tractography
Reconstructed “fibers”
Where do these fibers pass?
Which gray matter regions are inter-connected by white mater fibers?
Do structural properties of the fibers correlate with behavioral data?
These are not actual fibers, but streamlines that are the product of an arbitrary algorithm
Moreover, their reconstruction depends on the diffusion model

30. to DTI study – example I Linguistics Introduction
White Matter Structure Changes as Adults Learn a Second Language:
The authors investigate the role of adult structural plasticity in the complex, long-term learning process of second language acquisition.
DTI scans were acquired from 11 English speakers who took a 9-month intensive course in written and spoken Modern Standard Chinese as well as from 16 control participants who did not study a language.
FA increases linearly during language learning over 9 months.
Schlegel et al. 2012

31. to DTI study – example II Linguistics Introduction
Syntactic Processing Depends on Dorsal Language Tracts:
The authors aim to identify which white matter tract(s) are important for syntactic processing, by examining the relationship between white matter damage and syntactic deficits in patients with primary progressive aphasia (PPA).
Reduced FA in the left SLF/Arcuate was associated with deficits in syntactic comprehension (A) and production (B).
In contrast, there was no relationship between FA in the left ECFS and measures of syntactic comprehension (C) or production (D).
Wilson et al. 2011

32. Imaging The Human Brain
Introduction to
Linguistics
Imaging The Human Brain
Methods with a high temporal resolution
EEG – Electroencephalography
MEG – Magnetoencephalography

33. Introduction to
Linguistics
Electrical dipole

34. Electroencephalogram
Introduction to
Linguistics
Electroencephalogram
EEG is the measurement of electrical activity produced by the
brain as recorded from electrodes placed on the scalp.
The EEG was first recorded in humans by the German psychiatrist Hans Berger in 1929

35. Placement of electrodes
Introduction to
Linguistics
Placement of electrodes
EEG measurements can be obtained non-invasively by electrodes applied to the surface of the scalp
10-20
system

36. to Timing is everything Linguistics Introduction
Many neurons need to sum their activity in order to be detected by
EEG electrodes.
The timing of their activity is crucial -
Synchronized neural activity produces
larger signals.

37. Introduction to
Linguistics
From EEG to ERP

38. Introduction to
Linguistics
ERP Components

39. to The N400 Linguistics Introduction Kutas and Hillyard, 1980
Kutas and Federmeier, 2000

40. Some language related ERPs
Introduction to
Linguistics
Some language related ERPs
• N400 – modulated by the semantic consistency of a lexical
item in context
• ELAN (early left anterior negativity) - found in response to
phrase structure violations, reflects early syntactic processing
• LAN (left anterior negativity) – triggered by word category violations,
working memory demands, ambiguity..
• P600/SPS (syntactic positive shift) – modulated by syntactic
violations, reflects late syntactic reanalysis

41. to ELAN, LAN, P600 Linguistics Introduction
Black and grey spots reflecting ELAN and P600 differences
respectively, between the
correct and incorrect signals

42. Introduction to
Linguistics
Source Localization

43. to Advantages of ERP Linguistics Introduction
• High Temporal Resolution
• Measurement can be locked to a certain
event in a sentence
• Head movements are allowed
• More child friendly

44. Magnetoencephalograph
Introduction to
Linguistics
Magnetoencephalograph

45. to The SQUID Linguistics Introduction
Superconducting quantum interference device
SQUID detectors measure brain magnetic fields around 100 billion times weaker than earth’s steady magnetic field.

46. to MEG data Linguistics Introduction
MEG studies are very similar in practice to scalp-recorded electric field
potential studies

47. to MEG vs. ERP Linguistics Introduction
• MEG recording has a significant advantage
when compared to scalp-recorded ERPs:
• Magnetic fields are unimpeded by the high
resistance of the skull (the volume conduction
problem)
• In that sense, MEG measurements are more
similar to direct cortical recordings than to
scalp recordings
• But: if the primary current does not have a
component that is tangential to the surface of the skull, it
cannot be detected by MEG (for this reason, MEG and EEG
measurements are often obtained simultaneously)
• And the inverse problem still exits!