Lecture 7- TMS

Question 1

first person in the UK to report magnetically induced phosphenes

Answer 1

Thompson

Question 2

How does TMS work?

Answer 2

Pass an intense,rapidly varying, electrical current through a set of coils

Causes a strong but transient and rapidly changing magnetic field over a region of the scalp (2 Telsa)

This magnetic field induces a rapidly changing electrical field in the underlying brain tissue

Results in an extraneous flow of current that interacts with local neural processing
Rises (very brief pulse; 0.1ms) and dips within 1ms

Question 3

Two types of coil

Answer 3

Round coil

Figure of 8 coil

Question 4

Round coil?

Answer 4

More general disruption

Question 5

Figure of 8 coil?

Answer 5

Combination in the middle makes it more focal

Question 6

What is Barker’s model?

Answer 6

If magnetic field is parallel to axon, no induced current

If perpendicular, depolarisation can occur = disruption

Question 7

Disruptive mode?

Answer 7

Strong stimulation
Neural noise/brain lesion
e.g. Disrupting language areas while reciting

Question 8

What do we need to think about when designing TMS experiments?

Answer 8

People blink/move eyebrows/move shoulders

The noise TMS produces (need sham control condition)

Question 9

Productive mode?

Answer 9

Weaker stimulation
Can facilitate activation

Produces phosphenes/hand movements

Usually over primary areas

Question 10

TMS is what type of technique?

Answer 10

Interference technique

Question 11

TMS over primary motor area? (M1)

Answer 11

TMS depolarizes corticospinal tract neurons

Evokes contralateral hand muscle movements
as measured by MEP

Question 12

Is TMS constrained to stimulation site?

Answer 12

No…

Spreads into connected and functionally coupled areas (inc. subcortical areas)

Question 13

Allen et al

Answer 13

(2007)

Short rTMS trains (1-4s) at various frequencies in cat visual cortex

Question 14

In Allen et al’s (2007) study, there was an enhancement of spontaneous neural activity of up to ____ lasting up to ___ after TMS

Answer 14

200%

1 minute

Question 15

In Allen et al’s (2007) study, activity in the visual cortex evoked by sinusoidal gratings was suppressed up to __ after TMS and gradually recovered after ___

Answer 15

60%

10 minutes or longer

Question 16

In Allen et al’s (2007) study, they found that effects of TMS depend on ____ and ____

Answer 16

frequency and duration

Question 17

Based on Allen et al’s (2007) study, TMS disrupts the ___ relationship among ___ responses
Evidence?

Answer 17

phase
neural

Neural spikes were decoupled from ongoing oscillations for 30s across all frequency bands

Question 18

Based on Allen et al’s study, what type of coupling is there between TMS-evoked neural responses and changes in cerebral haemodynamics?
Evidence?

Answer 18

Tight!

TMS led to initial increase and longer decrease in tissue oxygenation

Question 19

Paus et al (1997)
Which method was CBF measured?
There is a ___ relationship between changes in CBF and ____ at the stimulation sight

Answer 19

PET
Positive
Number of trains

Question 20

Temporal resolution of TMS in behavioural studies

Answer 20

At least 10ms (Ashbridge et al, 1997)

Question 21

Temporal resolution?

Answer 21

Milliseconds to Seconds (depending on number of pulses)

Also depends on recovery rate of neural area

Question 22

Ilmoniemi et al (1997)

Answer 22

TMS applied to left sensorimotor area

As measured by EEG:
Response spread to adjacent ipsi motor area within 5-10 ms
Response spread to homologous area in opposite hemisphere within 20 ms

Question 23

There is a difference between physiological TMS and ___ TMS effect on behaviour

Answer 23

Functional

Question 24

Spatial resolution?

Answer 24

Not as good as fMRI but better than MEG and EEG

Question 25

Who 'invented' TMS?

Answer 25

Barker (1984)

Question 26

Stimulation depth?

Answer 26

Cannot stimulate medial or sub-cortical areas

Question 27

How can you elicit moving phosphenes?

Answer 27

Stimulate V5

Question 28

Repetitive TMS use and general findings

Answer 28

Behavioural tests can be administered during and after the rTMS rTMS can either enhance or impair performance on these tasks

Question 29

Single pulse use

Answer 29

Deliver single pulse to specific brain area at a specific time during a task Provides greater temporal resolution in assessing role of area in that task

Question 30

Three types of rTMS

Answer 30

``` High frequency (typically online) 5 pulses at 10Hz ``` Low frequency (typically offline) (before) 1 Hz rTMS for 10/15 minutes Lasts for 5-10 minutes ``` Theta burst (very high burst) 50 Hz Effects last a lot longer ```

Question 31

Critical time for TMS delivery coincides with time at which ____ can be recorded which is earlier than ___

Answer 31

single unit responses ERPS

Question 32

Two types of control in TMS experiments

Answer 32

Control task | Control site

Question 33

fMRI guided TMS neuronavigation

Answer 33

Best but most expensive method Have PS complete the same task in fMRI and TMS Can stimulate (with TMS) the most activated area (in fMRI)

Question 34

MRI guided neuronavigation

Answer 34

Anatomically identify the area of brain which you want to stimulate based on MRI

Question 35

TMS neuronavigation based on group coordinates

Answer 35

localise brain region via coordinates from other fMRI paper/study - doesn’t take into account individual anatomy

Question 36

TMS based on the 10-20 EEG system (anatomical landmark approach)

Answer 36

Conduct the same measurement as one would do for EEG | - not very precise

Question 37

Functional TMS localizer

Answer 37

For each PS, the site at which TMS provides maximal disruption in a different task is determined

Question 38

What did Sack et al find?

Answer 38

(2008) Compared fMRI, MRI, group coordinates and 10-20 system neuronavigation Determined how many PS were needed to gain sig. result fMRI: effect size = 1.13, only need 5 PS for sig. effect MRI: 0.82, only need 10 PS Talairach/group coordinate: 0.67, need 13 PS Landmark/EEG (P4): 0.3 - needed 45 PS

Question 39

Silvanto et al

Answer 39

(2007) Patient GY Blindsight patient but could detect and localise stimuli in the blind field Shows two pathways: 1) Retina --> PVC 2) Brainstem --> Higher visual areas TMS applied over V5 GY experienced TMS induced phosphenes in his blind field following bilateral stimulation THEREFORE V5 is necessary for awareness

Question 40

Gobel et al (2001) (double digits) | When TMS is applied over left angular gyrus, much ___ ___ for numbers larger than ___

Answer 40

larger RT | 65

Question 41

Gobel et al (2001) | There was no sig effect of TMS on double digit numbers when TMS was applied to ____

Answer 41

Left supra-marginal gyrus

Question 42

Gobel et al (2001) (single digits) | When TMS is applied over left supra-marginal gyrus, there is a significant ____ in ___ for numbers larger than ___

Answer 42

increase RT 5

Question 43

Gobel et al (2001) (single digits) | There was no sig effect of TMS on single digit numbers when TMS was applied to ____

Answer 43

Left Angular gyrus

Question 44

The size of the magnetic field generated with a TMS coil can be up to...

Answer 44

2.5 Tesla

Question 45

Which of these frequencies is NOT typically used when rTMS is applied to human subjects: 5 10 50 100

Answer 45

100

Question 46

What did the TMS experiment with the patient GY show?

Answer 46

GY experienced TMS induced qualia in his blind field, only with bilateral stimulation

Question 47

In Goebel et al. (2001) ____________ number comparison was significantly impaired when rTMS was applied over ___________________.

Answer 47

double digit/left angular gyrus

Question 48

Grotheer et al (2016)

Answer 48

TMS over right Number Form Area: gave them 2 pulses at 0ms and 100ms after stimulus presentation, found a decrease in accuracy for both letters and numbers. TMS over ILO (control): no significant effect on numbers or letters

Question 49

O'shea (2007)

Answer 49

Wanted to know if changes in brain activation after stroke are due to altered structure or reorganisation of function Two tasks: select (harder) or execute Select: more activation in premotor cortex compared to execute 1hz of TMS over LD PMC: increase in BOLD in right PMC (compensatory) (only for selection task) 1Hz of TMS over sensorimotor cortex: no increase in BOLD in right PMC THEREFORE Changes seen in stroke patients in right dorsal PMC are due to reorganisation of function

Question 50

What did d'Arsonval do?

Answer 50

Presented the first report of magnetically induced phosphenes in human subjects by stimulation of the retina, not the cortex Painless stimulation of the nervous system by electromagnetic induction

Question 51

Effects of a single TMS pulse may last up to ___ (but not all ___ ____)

Answer 51

70ms | physiologically active