Lecture 2 - Applications of TMS in Research Flashcards
What kind of inference does the TMS neural noise approach allow for that the probing excitability approach does not allow for?
The neural noise approach allows for the inference of causality. If a function (cognitive or motive) is impaired due to TMS being applied to a certain brain region, in can be inferred that that brain region is causally involved in that function.
Probing excitability on the other hand can show that a brain region is generally involved in a function, but not causally.
How does the “probing excitability” TMS approach use MEPs to measure brain activity?
The “probing excitability” approach of TMS involves applying a TMS pulse to usually the motor cortex and at a strength that will generate a motor response that can be measured. The response measured is known as the Motor Evoked Potential and is measured by an Electromyogram (EMG). The idea is that if the brain region is required for a cognitive task then it will already be activated when performing a certain cognitive task so when TMS is applied the MEP will be higher than if the task was not being performed.
It should be noted that the probing excitability approach can only show general involvement and not causal involvemnent.
Define MEP.
Motor Evoked Potential - the motor response induced by activation of the the brain area responsible for that movement by TMS.
Explain how paired-pulse TMS works when applied to two separate areas of the brain and what inferences can be made from data obtained using this method.
Paired-pulse TMS involves applying a sub-threshold TMS pulse to one area of the brain and then a supra-threshold pulse to another area of the brain and measuring whether the MEP generated at the second area is higher than when the first pulse was not applied. If it is then we can deduce that there has been information transfer between these areas.
Explain how paired-pulse TMS can be used to study neural activity decay of certain brain areas and give an example of how this approach has been used to study individual’s with Schizophrenia.
Applying a TMS pulse to a specific area at a sub-threshold voltage and then applying another pulse to the same area this time at a supra-threshold voltage and measuring MEPs we can determine whether or how long it takes for the activity of the brain area to decay.
It has been proposed that those who have Schizophrenia have areas in the brain that have impaired neural activity decay rates, i.e. it takes longer for neural activity to decay, dissipate. This paired-pulse TMS approach has been used to provide evidence to support this.
What is an example of a clinical application of TMS?
It has been proposed that depression is related to an imbalance of cortical activity between the two hemispheres of the brain. As a last resort for the treatment of depression TMS is sometimes applied to one hemisphere of the brain to help even out the imbalance.
What is an MEP?
Motor Evoked Potential
In TMS was is “Probing Information Transfer” approach and how does it work?
The TMS approach that can be used to determine whether there has been information transfer between two areas of cortex is called Paired-Pulse TMS.
It works by stimulating an area of cortex at a sub-threshold voltage and then stimulating another area at a supra-threshold voltage and measuring the MEPs. If there is higher than baseline MEPs when the paired-pulse TMS is done then we can assume that there has been information transfer between these two parts of the cortex.
What is another way to use paired-pulse TMS?
Paired-pulse TMS can be used to determine the rate of decay of activity in a certain area of cortex. Same principle of paired-pulses and measuring MEPs, however, in this case it is in the same area.
This has been used to show that people experiencing schizophrenia may have decreased neural activity decay in certain regions.
Can TMS be used as a clinical treatment option for people with severe depression?
Yes. However, with mixed effectiveness.
