TMS Flashcards

1
Q

What is TMS?

A
  • “Non-invasive” technique to create virtual cortical “lesions”, which are:
    • Temporary
    • Reversible
    • Localised
  • Alllowing us to understand function of specific brain regions.
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2
Q

Why can’t we always use patients in studying causality?

A
  • Insufficient patients with circumscribed lesions to study all cognitive functions.
  • Lesions in single, specialized areas are rare.
  • Recovery and brain plasticity might compensate for lesions over time.
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3
Q

How is TMS applied? (Go through the process)

A

TMS is applied externally via. a coil on scalp:

  • Produces a rapidly changing magnetic field
  • Induce electrical currents in the brain
  • Depolarize neurons in a small, circumscribed area of cortex
  • Neurons fire randomly, increasing neural noise, mask neurons which are firing correctly
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4
Q

What did these researchers find?

  1. Fritsch & Hitzig (1870)
  2. D’Arsonval (1896)
  3. Magnusson & Stevens (1911)
A
  1. Fritsch & Hitzig (1870)
    • Electrically stimulate the cortex of animals
  2. D’Arsonval (1896)
    • Discovered that the magnetic stimulation of the visual cortex can elicit “phosphenes”
  3. Magnusson & Stevens (1911)
    • Developed the first “head coil” covering the entire head
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5
Q

What is rTMS and what does it require?

A

rTMS is a modifiation of TMS where it creates fast sequence of pulses.

It requires:

  • Very fast loading times
    • 100-200 μs
  • Short duration
    • <1 ms
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6
Q

What is the most common coil in TMS?

How does it work and what is the advantage?

A

The most common coil in TMS is the Figure 8 Coil.

It works by:

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

Its advantage is that it has:

  • Strongest effect in centre with radius 3-4 mm
  • More precise stimulation and more focal of cortex compared to round coils
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7
Q

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

A

Injection of “neural noise” approach:

  • Using single-pulse TMS to disrupt cognitive processing.
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8
Q

What does the ‘neural noise’ approach establish and how do we do use it?

A
  • A single TMS pulse to a specific region of the cortex disrupts a cognitive function.
    • Establishes causality, unlike neuroimaging (correlations).
  • Interferes with process of interest at exactly the
    time window during which the brain regions are required by inducing “neural noise”
    • Interferes with normal functioning (Regions still work)
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9
Q

What are the overview and aim of “Neural Noise” Amassian et al. (1989)?

A

Overview

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

Aim

  • Effects on letter perception when varying the interval between visual stimuli and time point of TMS stimulation
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10
Q

What is the result of the “Neural Noise” by Amassian et al. (1989)?

A
  • Critical period (40 – 120 ms) stimulation
    • Affected detection performance
  • Shifting the stimulation site from left to right
    • Impaired perception of letters in the contra-lateral visual field
  • 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 as bone was in the way
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11
Q

What is the aim of “Neural Noise” by Amassian et al. (1993)?

A

Aim:

  • Find out whether ‘visual mask’ can itself be ‘masked’ using single-pulse stimulation, thereby ‘unmasking’ the stimulus
  • Since TMS disrupts stimuli, it could potentially disrupt processing of mask, thereby preventing that the stimulus is suppressed
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12
Q

What is the result of “Neural Noise”. Amassian et al. (1993) and what do their 2 studies tell us?

A

Critical Period:

  • 60-140ms (20ms more than first one)
  • TMS Informs us about time-course of processing

At 100ms

  • Without TMS, detection rate of target 0.37
  • With TMS, detection rate of target increased to 0.9
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13
Q

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

A

Using repetitive TMS to interrupt or enhance cognitive processing.

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14
Q

Why is rTMS used and what are the guidelines?

A
  • Inhibit cognitive functions for a longer period of time
  • rTMS before or during task
  • Measure whether (and for how long) a specific cognitive task is impaired
  • There are strict safety guidelines for rTMS
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15
Q

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

A

The “probing excitability” approach using single-pulse TMS.

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16
Q

What does the “Probing Excitability” approach test in particular?

A

The Motor System.

17
Q

What is the idea behind “Probing Excitability”?

What is the measure of interest and what does it not do?

A

Idea

  • 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
    • It does NOT aim to disrupt cognitive function and examine effect on performance
  • Measure MEPs for each stimulation and compare average MEPs between experimental conditions
18
Q

How does “Probing Excitability” measure M1 reaction?

A

Recording Motor Evoked Potential (MEP) using Electromyogram (EMG), which is electrical activity of muscles.

19
Q

What is the aim of the “Probing Excitability” study by Eisenegger et al. (2007)?

A

Aim: to find out whether M1 involved in MR.

20
Q

What is the result in the study of the “Probing Excitability” by Eisenegger et al. (2007)?

A
  • Stimulation of M1 during mental rotation elicited stronger MEPs as compared to baseline, reading aloud, reading silently
    • M1 is more excitable during mental rotation and might be already activated, and hence, involved in the cognitive process
21
Q

What is the aim of the “Probing Excitability” study by Bode et al. (2007)?

A

Aim: Is M1 dependent on strategy?

  • Has been suggested that some objects can easily be imagined as rotated by hand (e.g., tools) while others can’t (e.g., building)
22
Q

What is the Result and Limitations/Future Directions of the “Probing Excitability” study by Bode et al. (2007)?

A
  • MEPs were equally high for mental rotation of all different stimuli, so probably strategy does not play a role
  • M1 could be more excitable because adjacent and interconnected regions (e.g., SMA) were activated
23
Q

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

A

Probing information transfer using “Paired-pulse approach”.

24
Q

What is the logic behind “Paired-Pulse”?

A
  • Two pulses in brief succession
    • Sub-threshold
    • Supra-threshold
  • Examine how strongly the first pulse influences the effect of the second pulse
    • First pulse preactivates, what will happen to the second pulse?
25
Q

What is the overview of the “Paired Pulse” study by Fitzgerald et al. (2003)?

A
  • Schizophrenic suggested to have difficulty inhibiting motor cortex.
  • Reduced c_ortical silence period:_ Impaired suppression of tonic (slow) motor activity that follows descending excitatory activity
    • Cortical Silence Period: Cooling down period to get rid of motor activity

Study

  • Sub-threshold pulse
    • Produced excitatory activity in left M1
  • Supra-threshold pulse
    • Measured excitability via MEP
26
Q

What is the result of the “Paired Pulse” study by Fitzgerald et al. (2003)?

A
  • Compared to controls, patients with and without medication showed stronger responses to the second pulse.
    • i.e. cannot inhibit first sub-threshold pulse
  • Suggesting general deficits in motor inhibition.
27
Q

What is TMS mainly used for in clinical application and why?

A
  • Depression
    • Linked to PFC imbalance between hemispheres
    • TMS can stimulate PFC (one hemisphere) to balance it out
    • Last minute resort

Though it also works for other mental disorders.