7. TMS

Question 1

d’Arsonval (1896)

Beer (1902)

Thompson (1910)

Answer 1

Magnetically induced phosphenes (All were retinal stimulation).

• d’Arsonval presents 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)
• Thompson shows the same thing but on himself

Question 2

When was the first successful stimulation of the human motor cortex (TMS)?

Answer 2

1985

Question 3

How does TMS work?

Answer 3

Magnetic coil with current running in one direction creates an electric field which goes through the scalp and generates another magnetic field in the underlying tissue which runs in the opposite direction

Question 4

Figure of 8 TMS coil induced the strongest electrical field…

Answer 4

where the two loops meet, the induction is very focal under that spot

Question 5

What are the two modes of TMS?

Answer 5

Disruptive - induces neural noise

Productive - produces things such as phosphenes, hand movements

Question 6

What is the difference between TMS and fMRI/MEG?

Answer 6

• TMS is an interference technique (Aka virtual lesion technique)
• fMRI/MEG measure correlations (BOLD/magnetic fields related to behaviour)

Question 7

What are the different TMS protocols:

Answer 7

• Single pulse
• Trains of pulses (r(repetitive)-TMS):

e.g. high freq (typically when someone is doing a task - online): 5 pulses at 10Hz

e. g. low freq (typically when someone is not doing a task - offline): 1Hz rTMS for 10 mins
- —————————————-
- Theta burst: very high frequency of rTMS (50Hz; offline)

Question 8

How are hand muscle movements measured?

Answer 8

Using MEP

Question 9

TMS stimulation propagates into …

Answer 9

connected and functionally coupled areas, including subcortical areas

Question 10

Allen et al (2007) - physiological basis of TMS

• Stimulating cat visual cortex (short rTMS trains (1-4s) at various freqs (1-8Hz))

Answer 10

measured activity using single unit recording, haemodynamic recordings, local field potential tissue oxygenation

Key findings:

1. Fx more pronounced with longer trains and higher freq:

• spontaneous activity (unrelated to stimulus) up by up to 200%
• Activity resulting from stimulus in vis cortex suppressed by up to 60%

2. TMS disturbs phase relationship among neural responses
   - neural spikes were decoupled from ongoing oscillations
3. Tight coupling between TMS-evoked neural responses and changes in cerebral haemodynamics
   - initial increase and longer lasting decrease in tissue oxygenation and haemoglobin concentration

Question 11

Paus et al (1997) - TMS: spatial resolution

Answer 11

TMS & PET

• positive correlation between CBF and number of trains at the stimulation site
• Changes 1-2cm in diameter
• Observed also distal (away from focal point, connected regions) CBF changes

Question 12

Ilomoniemi et al. (1997) - TMS: spatial resolution

Answer 12

• EEG responses spread to other hemisphere within 20-30ms (distal changes)
• Difference between physiological TMS effect and functional TMS effect on behaviour (not strong to affect behaviour related to other hemisphere for example)

Question 13

Critical time for TMS delivery coincides with time at which _____ can be recorded (___)

Answer 13

single unit responses, (earlier than ERPs - would have to use it before a known ERP response occurs)

Question 14

Effects of a single TMS pulse may last up to ___ (but…)

Answer 14

70ms (but not all physiologically active 9 i.e. visible effect on behaviour)

Question 15

In behavioural studies, single TMS pulse lasts at least ___ (Ashbridge et al., 1997)

Answer 15

10ms

Question 16

Cooling is ____ technique

Answer 16

an interference

Question 17

What are the two features of best TMS studies?

Answer 17

• control tasks (e.g. interfering with language production, shouldn’t interfere with singing when stimulating the same area)
• control sites (e.g. predicting speech would be interfered by stimulating a certain area, there should be another area which you could stimulate and it wouldn’t interrupt speech)

Question 18

What is Brainsight 2?

Answer 18

Localising target location for TMS based on MRI

Question 19

what does fMRI-guided TMS neuronavigation involve?

Answer 19

Using location of a peak of fMRI activation contrast

Question 20

MRI-guided neuronavigation

Answer 20

Using MRI image to locate the area of interest (e.g. anterior IPS)

Question 21

TMS neuronavigation based on group coordinates

Answer 21

based on fMRI peak activation of a whole group

Question 22

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

Answer 22

Using for example the location of a P4 electrode

Question 23

Functional TMS localiser as a method of localisation for TMS sites

Answer 23

Stimulating the site which provides maximal disruption in a different task

Question 24

Sack et al. (2008)

compared the methods of localisation of sites for TMS using a number stroop task

Answer 24

• 3 TMS pulses when numbers displayed
• had to choose physically larger number (L or R?)
• CONGRUENT (larger number physically larger) FASTER RT than incongruent (smaller number physically larger)

using fMRI to localise caused greatest reduction in RT fx following TMS (Cohen’s d = 1.13)

• 5 participants needed with fMRI localisation for a sig effect
• EEG you need at least 50

!!!!!!!!fMRI provided the best TMS site for disrupting behaviour

Question 25

Silvanto et al. (2007) Patient GY (blindsighted - no left V1, no awareness) - when asked to guess about a stimulus in their blind field, they guess at an above chance level --------------------------------------------------------------------------- - GY has no perception of posphenes when stimulated over left V1 ------------------------------------------------------------------------- Uni/bilateral TMS over V5/MT applied, can he see something where he usually cannot perceive?:

Answer 25

Controls: can see moving posphenes with both uni & bilateral stim GY: Stimulating left V5 alone - still didn't see posphenes !!!!!!with stim of bilateral V5 GY reported awareness in the right visual field V1 necessary for awareness!

Question 26

Older visual pathway

Answer 26

Eyes -> brainstem -> higher order vis processing - concerned with reflexive behaviour, orienting towards something important

Question 27

Newer visual pathway

Answer 27

eyes -> thalamus -> visual cortex - conscious visual perception

Question 28

Which visual pathway is not working in blindsighted people?

Answer 28

Newer pathway (Eyes>thalamus>visual cortex)

Question 29

Number processing & TMS (Gobel et al., 2001) Visuospatial (angular gyrus) vs motor attention areas (supramarginal gyrus) *** (head maths vs finger maths) ***

Answer 29

2 areas in parietal cortex: - angular gyrus = visuospatial processing area - supramarginal gyrus = motor attention area - --------------------------------------------------------------------------- Task: is the 2-digit number bigger or smaller than 65? !!!!RT gets higher following TMS the closer to 65 the numbers are (distance effect) !!!!left angular gyrus (vis-spat processing area) + rTMS = even higher RT, especially for larger numbers (two digit numbers) !!!!supramarginal (motor attention area) + rTMS = same effect but with smaller numbers (5-10) !!!!!Think of counting small numbers on fingers when you are little, thus greater connection to the MOTOR attention area THIS IS A DOUBLE DISSOCIATION

Question 30

Grotheer, Herrmann & Kovacs (2016): Number Form Area (NFA) Discovery Where was it found?

Answer 30

Found a Number Form area in BOTH hemis - activation was higher for numbers compared to false numbers, letters and objects There is also a Letter Form area found only in the LEFT hemi

Question 31

Grotheer, Ambrus & Kovacs (2016): Disrupting the RIGHT Number Form Area (NFA) to investigate functionality

Answer 31

Decided to disrupt RIGHT number form area, this disrupted accuracy for Numbers BUT also, disrupted accuracy for Letters to a lesser extend (the previous study did not find activity for Letters in the RIGHT hemisphere)

Question 32

O'Shea et al (2007): Combining TMS & fMRI (Select vs execute task) r dorsal Premotor cortex: activity in stroke patients: - reorganisation of function?

Answer 32

In the SELECT (Choice) task, the participants had to press buttons with two different fingers, depending on which combination of shape-size they saw. In the EXECUTE (No choice) task the participants had to press a button when they saw a circle or a square. - SELECT task: higher activation of the dorsal premotor cortex... If Left DPC is damaged (stroke), the contralateral signal is going UP - ------------------------------- 1. Scanned healthy N - fMRI 2. Simulated the Left DPC lesion with TMS (15 min) 3. Scanned again - fMRI This led to an increase on the contralateral side of Dorsal Premotor Cortex just like in the stroke patients --------------------------------------------------------------------------- !!!This means that changes in stroke patients in right dorsal premotor cortex are DUE TO REORGANISATION OF FUNCTION !!!!and not only due to changes in brain structure resulting from stroke

Question 33

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

Answer 33

left angular gyrus

Question 34

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

Answer 34

2.5 Tesla

Question 35

What did the TMS experiment with the patient GY show?

Answer 35

GY experienced TMS induced qualia (conscious experience) in his blind field only with bilateral stimulation

Question 36

The first person in the UK to report magnetically induced phosphenes was

Answer 36

Thompson (1910)

Question 37

Who discovered electromagnetic induction?

Answer 37

Faraday (1832)