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MedSci 317 > Module A - Non-invasive brain stimulation > Flashcards

Module A - Non-invasive brain stimulation Flashcards

1
Q

Describe transcranial magnetic stimulation:

A

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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2
Q

Describe the side-effects of TMS:

A

Safe and painless for most people

A good way of activating cortical neurons in the brain

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3
Q

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

A

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

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4
Q

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

A 
I waves (produced by interneurons)
Inhibitory interneurons mainly synapse with interneurons
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5
Q

When does SICF occur?

A

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

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6
Q

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

A

Electrical stimulation induces D waves

LM and PA TMS induce late I waves

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7
Q

How can TMS be used to detect CNS conditions?

A

Can check if connections are present after stroke

Can observe a slowing of conduction velocities in MS

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8
Q

Where does the corticomotor pathway go?

A

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

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9
Q

What is the motor threshold (MT)?

A

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

Measured in % maximum simulator output

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10
Q

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

A

At least 0.05mV at rest

At least 0.10mV during activity

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11
Q

Describe recruitment curves of the corticospinal projections:

A

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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12
Q

Describe paired-pulse TMS:

A 
Test stimulus (produce an MEP)
Conditioning stimulus (precedes test stimulus, effect depends on intensity and inter-stimulus interval)
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13
Q

Describe short interval intracortical inhibitions (SICI):

A

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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14
Q

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

A

Inhibition (strokes are poor at this)

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15
Q

Describe long interval intracortical inhibition:

A 
Interstimulus intervals 50-200ms
Suprathreshold stimulus (conditioning stimulus BUT produces response)
GABAb-R activation
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16
Q

Describe short interval intracortical facilitation:

A

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

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17
Q

Describe the contralateral silent period:

A

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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18
Q

Describe interhemispheric inhibition:

A 
Interstimulus intervals 8-50ms
Suprathreshold stimuli
GABAb-ergic
Task-dependent modulation
In stroke, the normal side connections are lost
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19
Q

Describe the ipsilateral silent period:

A

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

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20
Q

Describe the general features of TMS:

A

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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21
Q

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

A

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

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22
Q

Describe the roles of the anode and cathode in TDCS:

A

Anode - depolarisation and increased excitability

Cathode - hyperpolarisation and decreased excitability

23
Q

Name the types of TDCS:

A 
Direct current
Alternating current (Bf 12.5-30Hz)
Random noise (0.1-600Hz)
24
Q

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

A

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

25
Q

Describe the use of TMS in diagnosis:

A

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

26
Q

How can TMS and TDCS be used in treatment:

A

TMS - depression, stroke, chronic pain

TDCS - stroke aphasia and neglect, tinnitus, ambylopia

27
Q

Describe the predication accuracy of non-invasive applications:

A

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

28
Q

Describe the use of the PREP algorithm for stroke patients:

A

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

29
Q

Describe the 72 hour mark of the PREP algorithm:

A

SAFE score >= 8 = Complete recovery (predicted recovery of upper-limb function at 12 weeks)

SAFE score < 5 progress to TMS at 5 days

30
Q

Describe the 5 days mark of the PREP algorithm:

A

TMS –> MEP present –> Notable recovery (SAFE 5, 6, 7)

MEP absent –> progress to MRI at 10 days

31
Q

Describe the 10 days mark of the PREP algorithm:

A

MRI asymmetry index limited recovery

MRI asymmetry index >0.15 –> no recovery

32
Q

Describe how to induce suppression and facilitation of repetitive TMS:

A

Low-frequency rTMS (~1Hz) = suppression

High frequency rTMS (5Hz) = facilitation

33
Q

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

A

Continuous (40s) = suppression

Intermittent (every 10s) = facilitation

34
Q

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

A

Given every 3 seconds

ISI of ~10ms = suppression
ISI of ~25ms = facilitation

35
Q

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

A

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

36
Q

Describe the mechanism responsible for the effects of TMS:

A

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

37
Q

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

A

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

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

38
Q

How do we know the effects of TMS work?

A 
Motor practice (stimulus-response)
With rTMS see a shift (definitely less excitable and opposite of motor practice)
rTMS resets people when M1 active (interferes)
39
Q

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

A

Learn fasted
Suppressed
Suppressed

40
Q

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

A

Decrease

Increase

41
Q

Describe the use of rTMS in depression:

A

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

42
Q

Describe the use of rTMS in stroke:

A

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)

43
Q

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

A

Facilitate ipsilesional cortex (same side) TMS facilitation

Suppress contralesional cortex (opposite side) TMS inhibtion

44
Q

Describe the effects of rTMS and TDCS in stroke:

A

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

45
Q

Describe how TDCS affects learning:

A

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)

46
Q

Describe the use of TDCS in tinnitus:

A

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

47
Q

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

A

Can improve depth perception when combined with visual training

48
Q

What is the intensity in rTMS and TDCS?

A

% threshold

Up to 2mA

49
Q

What is the duration of rTMS and TDCS?

A

How many stimuli?

How many minutes?

50
Q

Describe the strengths of non-invasive brain stimulation:

A

Targeted to specific part of brain

Specific effect depending on protocol

51
Q

Describe the limitations of non-invasive brain stimulation:

A

Equipment

Contraindications

52
Q

Describe the interindividual variability of non-invasive brain stimulation:

A

Suppressing contralesional M1 with cTDCS in stroke patients

  • Mild patients get better
  • Worse patients get worse
53
Q

Why should TMS not be tried at home?

A

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

MedSci 317 (7 decks)

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