Task 9 - TMS

Question 1

How does TMS function physically?

Answer 1

A strong current is induced in the coil. This change of electric current induces a magnetic field which penetrates the skull. Inside of the brain, the neurons function as another conductor, in which an electric current is induced by the magnetic field. This electric activation reduces the threshold of action potentials to a level where even noise causes them to fire.

Question 2

What is an important factor for how focused the magnetic field is?

Answer 2

The shape of the coil

Question 3

Name 4 advantages of TMS over normal lesions.

Answer 3

• No reorganization of the brain
• Enables WS designs
• Healthy brains can be investigated
• More precise localization of the disruption

Question 4

What is a limitation of spatial accuracy which applies to both TMS and naturally occurring lesions?

Answer 4

Diaschisis

Question 5

What is a limitation of TMS that is also found in fNIRS?

Answer 5

Only regions directly beneath the skull can be studied.

Question 6

Although TMS can activate certain brain areas, the effects need to be determined through averaging. Why is this?

Answer 6

Because the effects are too small otherwise. They are seen in average reaction times rather than the presence of behavior.

Question 7

What are the two main ways of applying TMS in studies?

Answer 7

as single pulses/short bursts during, or as prolonged stimulation before the task (rTMS).

Question 8

What are three ways of applying experimental control in TMS studies?

Answer 8

• Stimulation in critical vs non-critical time windows
• Stimulation in critical vs non-critical locations
• Task control: changing only aspects of the task, not timings or location of the TMS

Question 9

What needs to be considered regarding safety, before conducting a TMS study?

Answer 9

• rTMS has a very small risk of inducing a seizure.
• Electrical Implants should not be present
• Ear protection needs to be worn
• rTMS can have lasting effects which are difficult to predict.

Question 10

How does tDCS work?

Answer 10

A current is produced between an anode and a cathode. This current, similar to TMS interferes with the normal activity under one of the patches.

Question 11

____ stimulation tends to disrupt performance, while ____ stimulation rather improves performance.

Answer 11

Cathodal; Anodal

Question 12

For what can tDCS be used in a clinical setting?

Answer 12

Neurorehabilitation

Question 13

What is the difference between stimulation parameters and characteristics?

Answer 13

The parameters are about the properties of the physical stimulation. The characteristics refer to the induced physiological effects.

Question 14

How do stimulation parameters influence the characteristics?

Answer 14

Via the strength of the magnetic field

Question 15

What kind of stimulation can result in LTP?

Answer 15

Direct, high frequency (~5Hz and more)

Question 16

What kind of stimulation can result in LTD?

Answer 16

Direct, low-frequency (1Hz or less)

Question 17

The general relevance of a neural process can be investigated in what way?

Answer 17

rTMS before a task

Question 18

With TMS, what kind of experimental designs are made possible?

Answer 18

Using brain activation as the independent variable

Question 19

Which two factors determine the temporal resolution of TMS?

Answer 19

Duration of the pulse and duration of an area’s involvement in the task.

Question 20

Why did Sack et al. follow up on their study from 2002?

Answer 20

They found that both parietal lobes were active in a spatial imagery task, but only TMS stimulation to the right hemisphere disrupted task performance. So they were left with the question, why the left parietal area was active in the first place.

Question 21

In Sack et al.’s experiment from 2005, why did triple-pulse stimulation of the right PPC only disrupt performance when the left hemisphere was stimulated with rTMS?

Answer 21

If the left PPC is not stimulated, it can carry out the task normally while the right PPC was stimulated. If however, the left PPC is stimulated, the right PPC tries to take over, which is disrupted by the triple-pulse TMS.

Question 22

What are short-term effects of tDCS?

Answer 22

Influenced Membrane Potentials