Brain Stimulation Flashcards
What does TMS stand for?
Transcranial magnetic stimulation.
TMS uses electromagnetic induction. What does this mean?
A rapidly changing magnetic field creates a current in a conductive medium.
Describe how TMS apparatus stimulates the brain.
A stimulator delivers a large current into an attached TMS coil.
The TMS coil consists of loops of copper wiring in a plastic case.
This is placed on the scalp over the desired area to be stimulated.
How does neuronal depolarisation occur in TMS?
The magnetic field produced by the TMS coil induces a perpendicularly orientated electric field in the stimulated area.
Why are TMS coils commonly configured in a figure-of-eight shape?
It allows increasing focality of stimulation at the intersection of two loops of copper windings.
What is rTMS?
Repetitive TMS consists of trains of pulses separated by fixed intervals at specific frequencies.
What does low frequency (1Hz) rTMS induce?
Cortical inhibition.
What does high frequency rTMS induce?
Cortical excitation.
What does TBS stand for?
Theta-burst stimulation.
What is the effect of intermittent TBS (iTBS)?
Increases cortical excitability.
What is the effect of continuous TBS (cTBS)?
Decreases cortical excitability.
What is left-sided rTMS typically used to treat?
Significant anhedonia, melancholy and anergia.
What is right-sided rTMS typically used to treat?
Anxiety, PTSD, irritability or lability.
How do we determine that TMS is effectively stimulating the desired area?
Begin with stimulating the motor cortex.
Once a twitch is observed in the desired body part, sufficient stimulation has been achieved.
TMS coil can then be moved to stimulate the desired brain region.
What does tDCS stand for?
Transcranial direct current stimulation.
In one sentence, summarise tDCS.
A weak direct electrical current (<2.5mA) is passed between at least two electrodes, one of which must be placed on the head, to alter cortical excitability.
How does tDCS alter cortical excitability?
Via subthreshold modulation of neuronal RMPs.
Causes neuronal cells to be more or less likely to generate APs, depending on current direction.
Which configuration are tDCS electrodes typically placed in?
10-20 EEG system.
Describe how the anode affects cortical excitability in tDCS.
Current flows from the anode into the underlying tissue.
Neurons beneath have an increased likelihood of firing if appropriately orientated relative to current path.
Describe how the cathode affects cortical excitability in tDCS.
Current flows from the underlying tissue and into the cathode.
Neurons beneath are less likely to fire if appropriately orientated relative to current path.
Why is waveform not relevant to tDCS?
It uses direct current, which is simply “on” for the full duration of stimulation.
What is functional specificity?
Intrinsically active neuronal networks are preferentially modulated relative to non-active networks.
Why is functional specificity theoretically possible using tDCS?
Only neurons close to the AP threshold will be impacted by tDCS.
So it has a greater net effect on regions that are critically engaged in the targeted cognitive process.
What does ECT stand for?
Electroconvulsive therapy.
