Task 9 TMS Flashcards
1
Q
TMS (def)
A
method to magnetically stimulate focal regions of brain
2
Q
TMS methodology
A
- electromagnetic induction: stimulation of a region of cortex beneath current-carrying coil
- change of rate in electrical current –> generates magnetic field –> induces secondary electrical current to flow in nearby wire
- secondary electrical current induces neurons below stimulation site and causes them to fire (produce APs) as if they were responding to environmental stimuli
3
Q
Virtual lesion
A
- TMS can function as virtual lesion: temporarily interferes with ongoing cognitive activity in particular region
–> inference of necessity of a region for a particular task - brief pulse (1 ms) can lead to cortex effects lasting for 10ms
- TMS involves neuron activation from internal source (task demand) and external source (TMS)
–> interference between two activations
4
Q
Advantages of TMS over lesions
A
- no reorganization / compensation
- reversible effects
- can be used to determine timing of cognition
- focal lesion
- lesion can be moved within same patient
- study functional integration
5
Q
Disadvantages of TMS
A
- restriction of sites which can be stimulated
- spatial extent of TMS isn’t fully known –> distant brain regions may also get stimulation
6
Q
Advantages of lesions over TMS
A
- subcortical lesions possible
- accurate localization of lesions with MRI
- changes in behaviour/cognition more apparent
- accidents of nature can give insight into new patterns of behaviour
7
Q
Disadvantages of lesion studies
A
- cannot be used within-subjects
- brain organization
- brain injury could be larger than area under investigation
8
Q
Functional specialization
A
trying to understand functional contribution of particular regions to aspects of cognition
9
Q
Functional integration
A
- trying to understand how one region influences another or how cognitive functions influence each other
10
Q
Practical study designs of TMS: Timing
A
- timing of pulses is crucial
1. Single-pulse TMS: pulse delivery = variable: gives info on timing of cognition + necessity of brain region
2. rTMS: train of repetitive pulses during task = cannot tell about timing but more powerful in determining necessity
11
Q
Practical study designs of TMS: Position
A
- some assumptions about which brain region would be interesting to stimulate
- positions on head can be defined relative to landmarks (EEG system)
- Frameless stereotaxy: use of fMRI to locate candidate regions of stimulation
12
Q
Control
A
- Compare performance when region is stimulted in critical vs. non-critical time window
- Compare stimulation in critical and non-critical regions (other hemisphere for lateralized functio, adjacent regions to determine spatial size)
- Sham TMS: coil is held in air
- Task control: same region is stimulated but for another task
13
Q
Safety
A
- number + intensity of pulses
- exclude patients with epilepsy, pacemakers, etc.
- protect ears with earplugs
- not test same participant often within short interval
14
Q
tDCS
A
method using electrical currents to stimulate the brain
15
Q
Cathodal tDCS
A
- decreases cortical excitability = decreases performance: virtual lesion approach
- affects glutamate system (excitatory transmitter)
