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.
Which drug is used to prevent drooling during ECT?
Glycopyrrolate.
Which drug is used to prevent bradycardia during ECT?
Atropine.
Which drugs are used to prevent injury during ECT?
General anaesthesia and paralytics.
In one sentence, summarise ECT.
The application of an electrical current via unilaterally or bilaterally placed electrodes with the intent of inducing a generalised seizure.
In which patients can ECT be used?
Suicidal.
Catatonic.
Psychotic.
Bipolar affective disorder.
What does VNS stand for?
Vagal nerve stimulation.
How is VNS delivered?
Electrical stimulation of the vagus nerve occurs via an implanted electrode, which is connected to a pulse generator subcutaneously implanted in the chest wall.
How is VNS believed to work?
Vagus nerve afferents terminate in the nucleus solitary tract (NST).
VNS causes retrograde propagation of the electrical stimulation to the NST.
This modulates activity in afferent projection areas, e.g. the amygdala.
What does DBS stand for?
Deep brain stimulation.
How does DBS work?
Electrodes are surgically implanted in the brain via a burr hole, and connected to a subcutaneously implanted pulse generator.
The electrodes deliver electrical stimulation to subcortical or deep cortical structures.
How does DBS allow for variable anatomical specificity of stimulation from a single electrode?
Adjustable parameters, e.g. pulse width, frequency and amplitude/voltage, can be modulated through remote communication with the pulse generator.
What does FUS stand for?
Focused ultrasound.
Define ultrasound.
Mechanical pressure waves in a medium, e.g. air or tissue, with a fundamental frequency above the upper limit of human hearing (20kHz).
What is the main advantage of FUS?
Offers superior spatial resolution and the ability to stimulate subcortical structures noninvasively.
How does FUS work?
One or more ultrasound transducers are used to focus the energy at a specific target which can be deep within the brain.
What is the use of high intensity FUS (HIFUS)?
Ablation of specific brain targets.
What is the use of low intensity FUS (LIFUS)?
Being tested as a non-invasive and reversible neurostimulation techniques to inhibit or excite targeted regions.
