Task 9 - TMS

Question 1

Transcranial Magentic Stimulation (TMS)

Answer 1

• A coil placed on the scalp generates a strong magnetic pulse.
• Induces an electric current in the underlying brain tissue.
  Depending on stimulation settings:
  1. High-frequency TMS (≥5 Hz) increases neural activity.
  2. Low-frequency TMS (≤1 Hz) suppresses neural activity.
• Effects are temporary, allowing for reversible “virtual lesions” to study brain function.

Question 2

Principle that TMS is based on

Answer 2

The principle of electromagnetic induction:
* A change in electric current in a wire (the stimulating coil) generates a magnetic field, which can induce a secondary electric current in a wire placed nearby (or the brain)
* The greater the rate of change in the electric current, the greater the magnetic field

Question 3

Advantages of TMS compared to traditional lesion methods

Answer 3

• While real damage might result in reorganization (violation of transparency asumption) TMS does not
• Also makes within-subject designs possible (measuring before and after lesion)

Question 4

Disadvantages of TMS compared to traditional lesion methods

Answer 4

• Restricted to areas that can be stimulated (immediately beneath the skull) (like 2-3cm)
• Effects of TMS lesions are often not so “big”, don’t really show behavior change but more like slowed reaction times

Question 5

Single-Pulse TMS (spTMS)

TMS Protocol

Answer 5

• Delivers one isolated pulse at a time
• Disrupts brain activity for a very brief moment (milliseconds).
• Used to test how a specific brain area contributes to a task in real-time

Question 6

Repetitive TMS (rTMS)

TMS Protocol

Answer 6

Delivers a series of pulses at a set frequency over time
Can increase (high-frequency rTMS, ≥5 Hz) or decrease (low-frequency rTMS, ≤1 Hz) brain activity
Can suppress brain activity for minutes or longer

Question 6

Triple-Pulse TMS

TMS Protocol

Answer 6

• Delivers three pulses in quick succession (usually with a short delay)
• Generally not used for virtual lesions.
• Mainly used to study neural connectivity and inhibition/excitation interactions between brain areas

Question 7

Figure-of-Eight Coil vs. Circular coil/Single coil

Answer 7

Figure-of-eight: Focuses the magnetic field more precisely, which makes it ideal for targeting specific brain regions.
Circular: Produces a less focused magnetic field compared to the figure-eight coil

Question 8

Transcranial direct current stimulation (tDCS)

Answer 8

• tDCS uses two pads, cathodal and anodal, between which there is a small flow of electric current
• Cathodal tDCS stimulation tends to disrupt performance
• Anodal tDCS stimulation tends to enhance performance
• So you have to decide what effect you want on the region of interest and place the other in a region that is not interesting to you

Question 9

Spatial specificity of TMS

Answer 9

The magnetic field produced by TMS is not spatially focal (in theory its infinite)
But: The distribution of the induced electric field can be modelled to the point where scientists can be specific with the site of activation with a resolution of a few milimeters

Question 10

How to decide on TMS location

TMS protocol

Answer 10

• Can be positioned based on landmarks in the brain
• You can stimulate different spots on a grid and look at behavioral effects after
• Use MRI/fMRI beforehand