Task 9 Flashcards
How does TMS work ?
- > A brief, high amplitude pulse of current is discharge in a electromagnetic coil
- > The change in electrical current in coil generates a magnetic field
- > The magnetic field induces a secondary electrical current in the tissues
- > neurons fire
Name the short version how the TMS work:
-> Electric current in stimulating coil produces magnetic field which produces current induced in brain
How does TMS deactivate a region of intrest ?
- > Generally we are doing tak while applying TMS
- > Neurons fire due to task (internal source ) and due to excitation induced by TMS (external source)
- > The activation of internak source and external source corss cancel each other
What is a well known Metaphor for describing the effect of TMS ?
-> TMS signals are just like noise
What do we do with TMS ?
- > Enhance cognitive function / treatment
- > Identify functional specialization
- > Functional integration ( how one brain region influences another )
What are in general side effects of TMS ?
- > In general Effects of single TMS pulse are quickly reversible
- > But :
1. Epileptic seizures (if high frequency & intensity)
2. Potential permanent physiological changes
3. rTMS can cause suppression / unterdrückung of stimulated area that lasts for hours (usually mild)
4. Stimulus intensity should always be defined according to individual cortical excitability
What is the SET UP of TMS ?
- > Main power-pulse generation unit = Produce the high discharge current
- > Electromagnetic Stimulating Coil = apply magnetic pulses up to several Tesla
What is important to know about the shape of the coil ?
- > The shape and size determine how focal / focused the induced current is
- > Small = more focal / stronger / but field strength decreases more rapidly
What is the most commonly used stmulating coil ?
- > The butterfly / figure of eight coil
- > Important: the focal point of stimulation lies at the intersection of the two loops
Name another coil besides the figure eight coil:
-> Circular coil -> The focal ponts lays on the ring
How far can a TMS effect cortical areas ?
2 / 3 cm
Name one fact about spatial resolution:
-> Can not go to deep bcs stimulating deeper structures may also stimulate overlying cortex
Name so fact about the temporal resolution:
- > Point of maximal activation: stimulated area will have its lowest signal-to-noise ratio with respect to the task it is trying to perform
- > as neurons recover, the signal will increase
What is the impact of TMS on EEG and MEG signals ?
-> an effectively disrupted pulse will interfere with processes that contribute to the buildup of ERP/MEG signal (components)
What are the advantages of TMS over lesion studies ?
- > Effects are brief and reversible / no plasticity
- > Better temporal resolution
- > Stimulated location can be removed or moved
- > Within subjects design are doable
- > More specific since damage can be controlled
What do lesion studies and TMS studies have in common ?
-> Both identify neccesisty of brain areas
Which method is highly used in combination with TMS to infer the region to be actiavted:
-> FMRI
What are the advanatges of lesion studies over TMS ?
- > Subcortical lesions can be studied
- > Changes in behavior/ cognition are more observable in TMS mostly only present in reaction time
What is the main advnatge of TMS ?
-> Effect are reversable and not long lasting
What is are single pulse TMS ?
- > Also know as event related TMS
- > a single magnetic pulse is delivered at a precise time during a task
- > TMS pulse is delivered in different time windows
- > Provides information about the timing of cognition & and necessity
- > Activation directly impacts brain
What is meant by repetitive TMS ?
- > a train of pulses is applied during the task
- > Its about the effect after the stimulation
- > Causes plasticity via high freuency and low frequency impulses
What type of control condition do we use in TMS ?
- > compare stimulation in critical and non-critical regions
- > Task control (same region is stimulated but some aspects of the task have changed)
- > compare performance when the same region is stimulated in critical and non-critical time windows
- > Sham condition
Why is TMS so cool ?
-> Because in TMS studies brain activity is the independent variable and task performance the dependent
What does Sham condition mean?
-> Just using a fake coil as a control condition
