W1 - TMS

Question 1

What is TMS

Answer 1

“Non-invasive” technique to create virtual cortical “lesions”.

Question 2

What are the basic properties of TMS and what does it allow us to understand

Answer 2

• Temporary
• Reversible
• Localized

Allows us to understand function of specific brain regions

Question 3

How is TMS applied. Go through the process

Answer 3

Externally - via a coil placed on the scalp

1. ) Rapidly change magnetic field to
2. ) Induce electrical currents in the brain
3. ) Current depolarize neurons in a small, circumscribed area of cortex
4. ) TMS-induced current causes neurons to fire randomly > neural noise increase > mask neurons which are firing correctly.

Question 4

What is rTMS

Answer 4

Modifiation of TMS where it creates fast sequence of pulses

Question 5

How does rTMS create a magnetic field strong enough for stimulation. What are the 2 requirements

Answer 5

Very fast loading times (~100-200 μs) and short duration (<1 ms)

Question 6

What is the most common coil in TMS

Answer 6

Figure 8 Coil

Question 7

How does the figure 8 coil generate currents. What is the result compared to round coils?

Answer 7

• Generates magnetic fields in the opposite direction
• Generates offset current loops that circulate in opposite directions

More precise stimulation and more focal of cortex compared to round coils

Question 8

What is the advantage of have a more focal area stimulated

Answer 8

The researcher knows which part of the cortex is affected

Question 9

What is the first way TMS can be used to Bio Psych research

Answer 9

Injection of “neural noise” approach: Using single-pulse TMS to disrupt cognitive processing

Question 10

What is the logic behind the ‘neural noise’ approach

Answer 10

If single TMS pulse to specific region of cortex disrupts cognitive function > CAUSALITY (unlike neuroimaging)

Question 11

How do we use the ‘neural noise’ approach

Answer 11

Interfere with the process of interest at exactly the

time window during which the regions is required

Question 12

‘Neural noise’: Do the regions associated with the process of interest stop working completely?

Answer 12

Region does not STOP working but the ‘neural noise’ interferes with it

Question 13

“Neural Noise” Amassian et al. (1989): Overview of their study and Aim

Answer 13

Overview:

• 3 alphabetical letters as stimuli presented under difficult viewing conditions
• Magnetic stimulation was applied ~ 2 cm
  above the inion over visual cortex

Aim:

Effects on letter perception when varying the interval
between visual stimuli and time point of TMS stimulation

Question 14

“Neural Noise” Amassian et al. (1989): Results of their study

Answer 14

1.) Critical period (40 – 120 ms) stimulation affected
detection performance

2. ) Shifting the stimulation site from left to right impaired perception of letters in the contra-lateral visual field
3. ) Shifting TMS stimulation from top to bottom at midline (letters displayed vertically) > stimulation above the reference line suppressed letters at the bottom of the display [Stimulating below the centre not possible due to bone]

Question 15

“Neural Noise”. Amassian et al. (1993). Aims of their study

Answer 15

Aim: Find out whether ‘visual mask’ can itself be ‘masked’ using single-pulse stimulation, thereby ‘unmasking’ the stimulus

(Since TMS disrupts stimuli, can it disrupt mask?)

Question 16

“Neural Noise”. Amassian et al. (1993). Results of their study. And what does their 2 studies tell us

Answer 16

Without TMS, detection rate of target 0.37 at 100ms. With TMS, detection rate of target 0.9.

Critical Period: 60-140ms

Informs us about time-course of processing

Question 17

What is the second way TMS can be used to Bio Psych research

Answer 17

“Virtual lesion” approach: Using repetitive TMS to interrupt or enhance cognitive processing

Question 18

How does “Virtual lesion” via. rTMS work and why is it good

Answer 18

Inhibit cognitive functions for a longer period of time > Measure whether/how long a specific cognitive task is impaired

Question 19

What is the third way TMS can be used to Bio Psych research

Answer 19

The “probing excitability” approach using single-pulse TMS

Question 20

What does the “Probing Excitability” approach test in particular

Answer 20

For the Motor System

Question 21

What is the idea behind “Probing Excitability”. What is the measure of interest and what does it NOT do

Answer 21

If M1 is required for a cognitive task, then it should already be activated when single-pulse TMS is delivered.

Measure of Interest: How strongly M1 reacts to the pulse,

What does it NOT do: It does aim to disrupt cognitive function and examine effect on performance

Question 22

“Probing Excitability”: How does it measure M1 reaction

Answer 22

Using Motor Evoked Potential (MEPs), measured using Electromyogram (EMG) which is electrical activity of muscles

Question 23

“Probing Excitability”. Eisenegger et al. (2007): Aim

Answer 23

Aim: Is M1 involved in MR

Question 24

“Probing Excitability”. Eisenegger et al. (2007): Result

Answer 24

• Stimulation of M1 during mental rotation elicited stronger MEPs as compared to baseline
• M1 is more excitable during mental rotation and might be already activated, and hence, involved in the cognitive process

Question 25

"Probing Excitability". Bode et al. (2007) Aim

Answer 25

Aim: Is M1 dependent on strategy?

Question 26

"Probing Excitability". Bode et al. (2007) Result

Answer 26

MEPs were equally high for mental rotation of all | different stimuli, so probably strategy does not play a role

Question 27

"Probing Excitability". Bode et al. (2007) Limitation

Answer 27

``` M1 could be more excitable because adjacent and interconnected regions (e.g., SMA) were activated ```

Question 28

What is the fourth way TMS can be used to Bio Psych research

Answer 28

“Paired-pulse approach” : Probing information transfer

Question 29

What is the logic behind "Paired-Pulse"

Answer 29

Two pulses in brief succession – sub-threshold and supra-threshold Examine how strongly the first pulse influences the effect of the second pulse.

Question 30

"Paired Pulse" Fitzgerald et al. (2003). Aim and Methods

Answer 30

Schizophrenic difficulty to inhibit motor cortex. Produced the excitatory activity by a first TMS stimulus to the left motor cortex, and measured the excitability by assessing the effect of a second pulse (via MEPs)

Question 31

What is the Cortical Silence Period in Schizophrenic Patients

Answer 31

Cooling down period to get rid of motor activity. A period of suppression of tonic motor activity that follows descending excitatory activity

Question 32

"Paired Pulse" Fitzgerald et al. (2003). Results

Answer 32

Compared to controls, patients with and without medication showed stronger responses to the second pulse. i.e. cannot inhibit first sub-threshold pulse

Question 33

What is TMS mainly used for in clinical application

Answer 33

Depression. (Though works for other mental disorders)

Question 34

Why does TMS work for depression

Answer 34

Depression is linked to in imbalance of prefrontal activity between hemispheres TMS can stimulate prefrontal cortex to balance it out.

Question 35

Where is the effect of the 'figure-8' coil the strongest

Answer 35

Strongest effect in centre with radius 3-4 mm