The Lesioned Brain

Question 1

what is TMS ?

Answer 1

• Transcranial Magnetic Stimulation
• a means of disrupting normal brain activity rhythms by introducing neural noise

Question 2

what is an effect of TMS ?

Answer 2

a virtual lesion

mimic what a lesion in the brain might do

Question 3

what does TMS use to work ?

Answer 3

the electromagnetic properties of the brain, through the principle of electromagnetic induction

Question 4

who disocvered the principle of magnetic induction ?

Answer 4

Michael Faraday

Question 5

how does Faraday’s Coil work ?

as a part of TMS

Answer 5

(iron ring with wire)
- when connected to electricity there is a change in the magnetic field around it
- this induces an electrical current in the conductor (not connected to electrical source)

Question 6

how does TMS work ?

Answer 6

• generator produces a high amount of current, which creates a strong magnetic field
• to induce an electrical field in the brain, magnetic field has to be changing, so machine switches on and off at a high rate
• this interferes with electrical field in our brain, and then we can observe any behavioural changes which we can then measure using tradition methods

we hold a paddle over the area we want to stimulate

Question 7

what is the typical magnetic strength of a TMS generator ?

Answer 7

1.5 - 2 Tesla

same as MRI machine

Question 8

what is Tesla a measure of ?

Answer 8

magnetic flux

Question 9

what is an example of using TMS in studies?

Answer 9

• Task (e.g. reading) activates a neural network comprised of different brain areas
• We can Apply TMS pulse at any cortical node/area of network
• TMS will interfere with relevant neural signal; efficacy of signal will be degraded
• and we can observe changes in behaviour (e.g reaction time may change: takes us longer to read)

some areas will be task critical, and this will be reflected when TMS is applied to cortical area and it changes behaviour

Question 10

what does TMS do to task performance ?

Answer 10

can either enhance or reduce performance

TMS allows us to observe this behavioural change

Question 11

what are some advantages of TMS ?

Answer 11

• we can control location of stimulation
• transient and reversible (effects are not permenant/diminish once coil removed)
• virtual lesion technique
• establishes a causal link of different brain areas and a behavioural task (whether its crucial or supporting)