Module A - Non-invasive brain stimulation Flashcards by R M

Describe transcranial magnetic stimulation:

Use a plastic covered coil and a capacitor with a huge charge
This creates a brief magnetic field (2.2T ~50ms (most clinically induced magnetic fields are 1.5T)
The magnetic field strength decays exponentially
Perpendicular direction to coil has eddying currents in the opposite direction

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Describe the side-effects of TMS:

Safe and painless for most people

A good way of activating cortical neurons in the brain

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What results from local depolarisation of the axonal membrane induced by TMS and how are these results detected:

Evoked neural activity (EEG)
Changes in blood flow and metabolism (PET, fMRI)
Muscle twitch (EMG)
Behavioural changes

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What type of waves are produced when a single TMS pulse is applied?

I waves (produced by interneurons)
Inhibitory interneurons mainly synapse with interneurons

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When does SICF occur?

Short interval cortical facilitation occurs when S2 follows S1 by temporal summation

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Which types of stimulation induce D waves and late I waves?

Electrical stimulation induces D waves

LM and PA TMS induce late I waves

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How can TMS be used to detect CNS conditions?

Can check if connections are present after stroke

Can observe a slowing of conduction velocities in MS

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Where does the corticomotor pathway go?

From the motor cortex to the spinal cord to the motor unit

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What is the motor threshold (MT)?

Weakest stimulus that will produce an MEP on 4/8 trials

Measured in % maximum simulator output

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What are the MEP amplitudes at rest and during muscle activity?

At least 0.05mV at rest

At least 0.10mV during activity

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Describe recruitment curves of the corticospinal projections:

Increasing stimulus intensity increases the amplitude of the MEP
Slope is a measure of corticomotor excitability
Recruitment of neurons (lowest firing threshold first)
Recruitment of motor units (smallest first)
Affected by background muscle activity

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Describe paired-pulse TMS:

Test stimulus (produce an MEP)
Conditioning stimulus (precedes test stimulus, effect depends on intensity and inter-stimulus interval)

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Describe short interval intracortical inhibitions (SICI):

Interstimulus intervals between 1 and 5 ms
Conditioning stimulus between 60% and 100% of active motor threshold
GABAa-R activation
Reduced prior to movement
ISI (interspike intervals) 2-3ms
Sychronise to reduce inhibition or syncopate to increase inhibition

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What is the output of the motor system a result of?

Inhibition (strokes are poor at this)

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Describe long interval intracortical inhibition:

Interstimulus intervals 50-200ms
Suprathreshold stimulus (conditioning stimulus BUT produces response)
GABAb-R activation

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Describe short interval intracortical facilitation:

Specific inter-stimulus intervals
Suprathreshold stimuli
Synchronised I-waves: I-wave facilitation

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Describe the contralateral silent period:

Single test stimulus
During voluntary muscle activity
Silent period duration depends on GABAb-R activity
(shown as MEP followed by silent period)

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Describe interhemispheric inhibition:

Interstimulus intervals 8-50ms
Suprathreshold stimuli
GABAb-ergic
Task-dependent modulation
In stroke, the normal side connections are lost

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Describe the ipsilateral silent period:

Single test stimulus
Ipsilateral to activated muscle
Duration depends on GABAb-ergic activity

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Describe the general features of TMS:

Versatile research tool
Can measure cortical excitability
Measure GABAA and GABAB function with sub-millisecond precision
Can be used to measure effects of aging, maturation, neurological disorders, interventions in drugs, rehab, learning
Safe, non-invasive and painless

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Describe the properties of transcranial direct current stimulation (TDCS):

1-2mA current, up to 20 minutes
Moves ions through ECF
Shifts resting membrane potential
Alters spontaneous firing rate

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Describe the roles of the anode and cathode in TDCS:

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Anode - depolarisation and increased excitability

Cathode - hyperpolarisation and decreased excitability

Name the types of TDCS:

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Direct current
Alternating current (Bf 12.5-30Hz)
Random noise (0.1-600Hz)

What can the full range of TMS techniques be used to measure:

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Cortical excitability
Intracortical inhibition and facilitation
Interhemispheric interactions
Behaviour - learning, memory, mood, perception

Describe the use of TMS in diagnosis:

Conduction velocity, functional weakness (conversion disorder, where TMS can rule out a biological cause to localised weakness) Acute injury - Stroke, spinal cord injury, peripheral nerve injury and functional weakness Chronic conditions - multiple sclerosis, ALS

How can TMS and TDCS be used in treatment:

TMS - depression, stroke, chronic pain | TDCS - stroke aphasia and neglect, tinnitus, ambylopia

Describe the predication accuracy of non-invasive applications:

PT - 41% incorrect Model - 30% incorrect PREP - 17% incorrect

Describe the use of the PREP algorithm for stroke patients:

Accurate 83% of the time (vs. 50 PT scanner) More specific prognosis Measures brain (not just arm)

Describe the 72 hour mark of the PREP algorithm:

SAFE score >= 8 = Complete recovery (predicted recovery of upper-limb function at 12 weeks) SAFE score < 5 progress to TMS at 5 days

Describe the 5 days mark of the PREP algorithm:

TMS --> MEP present --> Notable recovery (SAFE 5, 6, 7) MEP absent --> progress to MRI at 10 days

Describe the 10 days mark of the PREP algorithm:

MRI asymmetry index limited recovery MRI asymmetry index >0.15 --> no recovery

Describe how to induce suppression and facilitation of repetitive TMS:

Low-frequency rTMS (~1Hz) = suppression | High frequency rTMS (5Hz) = facilitation

Describe how to induce suppression and facilitation of theta-burst stimulation:

Continuous (40s) = suppression | Intermittent (every 10s) = facilitation

Describe how to induce suppression and facilitation of paired associated stimulation (PAS):

Given every 3 seconds ISI of ~10ms = suppression ISI of ~25ms = facilitation

Describe how to induce suppression and facilitation of transcranial direct-current stimulation (TDCS):

Given continuously for >5 min Cathodal = suppression Anodal = facilitation

Describe the mechanism responsible for the effects of TMS:

NMDA-R dependent, effects are blocked by NMDA-R antagonists dextro methorphan and memantine Calcium influx - rapid influx promotes LTP - slow influx promotes LTD

Describe the results of a rapid and slow influx of calcium on AMPA receptors:

Rapid influx causes increase in number and density of AMPA-R (LTP) Slow influx causes decrease in number and density of AMPA-R (LTD)

How do we know the effects of TMS work?

``` Motor practice (stimulus-response) With rTMS see a shift (definitely less excitable and opposite of motor practice) rTMS resets people when M1 active (interferes) ```

Is their learning suppression or facilitation in the following TBS situations: iTBS imTBS cTBS

Learn fasted Suppressed Suppressed

rTMS can be used to disrupt signalling to ______ learning and facilitate signalling to ______ learning:

Decrease | Increase

Describe the use of rTMS in depression:

Suppresion of prefrontal cortex Usually subthreshold 1Hz rTMS (weak --> no MC response --> suppressive LTD) Several session required FDA approved treatment as a last resort

Describe the use of rTMS in stroke:

Helps people learn better during physiotherapy Brain stimulation needs to be combined with physical therapy for motor rehabilitation Most studies are at the chronic stage (caveat)

Describe how TMS can overcome the effect of the good side of the brain becoming overactive and oversuppressing the stroke side in stroke:

Facilitate ipsilesional cortex (same side) TMS facilitation Suppress contralesional cortex (opposite side) TMS inhibtion

Describe the effects of rTMS and TDCS in stroke:

Can improve upper limb function Can improve communication Can reduce visuospatial neglect (where people stop attending to one side)

Describe how TDCS affects learning:

TDCS improve and activates whole motor network Met carriers (BDNF) have reduced skill (10%) Val/Val in 2/3 population, higher level of learning Changes through use and experience (promote more permissible environment to LTP learning synapses)

Describe the use of TDCS in tinnitus:

10% of people have it but can be incredibly disabling for some people Can reduce the loudness and annoyance of symptoms Anode to facilitate left temporoparietal area Dose response

Describe the use of TDCS in ambloyopia (lazy eye):

Can improve depth perception when combined with visual training

What is the intensity in rTMS and TDCS?

% threshold | Up to 2mA

What is the duration of rTMS and TDCS?

How many stimuli? | How many minutes?

Describe the strengths of non-invasive brain stimulation:

Targeted to specific part of brain | Specific effect depending on protocol

Describe the limitations of non-invasive brain stimulation:

Equipment | Contraindications

Describe the interindividual variability of non-invasive brain stimulation:

Suppressing contralesional M1 with cTDCS in stroke patients - Mild patients get better - Worse patients get worse

Why should TMS not be tried at home?

Electrodes are very small TDCS affects a lot of the brain No idea of maximum safe dose Brain doping?

Module A - Non-invasive brain stimulation Flashcards

(53 cards)