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PSYC20006 - Bio Psych > W1 - TMS > Flashcards

W1 - TMS Flashcards

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1
Q

What is TMS

A

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

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2
Q

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

A
  • Temporary
  • Reversible
  • Localized

Allows us to understand function of specific brain regions

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3
Q

How is TMS applied. Go through the process

A

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.
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4
Q

What is rTMS

A

Modifiation of TMS where it creates fast sequence of pulses

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5
Q

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

A

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

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6
Q

What is the most common coil in TMS

A

Figure 8 Coil

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7
Q

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

A
  • 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

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8
Q

What is the advantage of have a more focal area stimulated

A

The researcher knows which part of the cortex is affected

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9
Q

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

A

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

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10
Q

What is the logic behind the ‘neural noise’ approach

A

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

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11
Q

How do we use the ‘neural noise’ approach

A

Interfere with the process of interest at exactly the

time window during which the regions is required

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12
Q

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

A

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

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13
Q

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

A

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

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14
Q

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

A

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

  1. ) Shifting the stimulation site from left to right impaired perception of letters in the contra-lateral visual field
  2. ) 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]
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15
Q

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

A

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?)

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16
Q

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

A

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

17
Q

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

A

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

18
Q

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

A

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

19
Q

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

A

The “probing excitability” approach using single-pulse TMS

20
Q

What does the “Probing Excitability” approach test in particular

A

For the Motor System

21
Q

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

A

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

22
Q

“Probing Excitability”: How does it measure M1 reaction

A

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

23
Q

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

A

Aim: Is M1 involved in MR

24
Q

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

A
  • 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
25
Q

“Probing Excitability”. Bode et al. (2007) Aim

A

Aim: Is M1 dependent on strategy?

26
Q

“Probing Excitability”. Bode et al. (2007) Result

A

MEPs were equally high for mental rotation of all

different stimuli, so probably strategy does not play a role

27
Q

“Probing Excitability”. Bode et al. (2007) Limitation

A 
M1 could be more excitable because adjacent and
interconnected regions (e.g., SMA) were activated
28
Q

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

A

“Paired-pulse approach” : Probing information transfer

29
Q

What is the logic behind “Paired-Pulse”

A

Two pulses in brief succession – sub-threshold and supra-threshold

Examine how strongly the first pulse influences the effect of the second pulse.

30
Q

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

A

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)

31
Q

What is the Cortical Silence Period in Schizophrenic Patients

A

Cooling down period to get rid of motor activity.

A period of suppression of tonic motor activity that follows descending excitatory activity

32
Q

“Paired Pulse” Fitzgerald et al. (2003). Results

A

Compared to controls, patients with and without
medication showed stronger responses to the second pulse.

i.e. cannot inhibit first sub-threshold pulse

33
Q

What is TMS mainly used for in clinical application

A

Depression. (Though works for other mental disorders)

34
Q

Why does TMS work for depression

A

Depression is linked to in imbalance of prefrontal activity between hemispheres

TMS can stimulate prefrontal cortex to balance it out.

35
Q

Where is the effect of the ‘figure-8’ coil the strongest

A

Strongest effect in centre with radius 3-4 mm

PSYC20006 - Bio Psych (13 decks)

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