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Rehabilitating the Brain > L6 - Brain Stimulation > Flashcards

L6 - Brain Stimulation Flashcards

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1
Q

What does TES stand for and what is the general idea/mechanism?

A

Transcranial electrical stimulation:

Uses two electrodes on the head, and drives a current between them to induce changes in certain brain areas.

It isn’t powerful enough to trigger the neurons themselves, but it increases their later excitability.

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2
Q

What does TDCS stand for?

A

Transcranial direct current stimulation.

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3
Q

What type of current does TES use?

A

Low intensity (0.5-2 mA) current, flowing from the anodal to the cathodal electrodes.

  • mini amps
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4
Q

What is the respective effects of anodal and cathodal stimulation?

A

Anodal (positive) stimulation depolarises the brain and cathodal (negative) stimulation hyperpolarises the brain.

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5
Q

What does TRNS stand for?

A

Transcranial random noise stimulation

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6
Q

What does TACS stand for?

A

Transcranial alternating current stimulation

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7
Q

What does ECT stand for?

A

Electrical convulsive therapy

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8
Q

What does ECT do?

A

Essentially, almost induces an epileptic seizure in the brain. So powerful it has to be supplied under general anaesthetic.

It recalibrates the brain and can induce long term changes such as mood.

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9
Q

What does TRNS do?

A

Supplies an unpredictable, jagged pattern of stimulation for 2-3 minutes.

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10
Q

What does tDCS do?

A

Supplies a constant current for a longer period of time (10-20 minutes) between two electrodes

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11
Q

What does tACS do?

A

Supplies a changing current between two electrodes.

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12
Q

If the current supplied through stimulation is suddenly increased from 0 to the maximum range, what happens?

A

The scalp is stimulated as well as the related brain area, leading to discomfort in the patient.

Techniques should therefore increase the current as gradually as possible, not only to limit discomfort but also to maximise the stimulation to the brain, rather than the scalp.

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13
Q

How does activity reflect features of the brain?

A

Weaker or greater activation depending on the folding of the brain in that area.

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14
Q

Which areas are activated with TES?

A

Definitely the target area will be activated, but it is highly likely that many other areas between the electrodes will also be activated.

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15
Q

What are the alternative electrode placement locations? Evaluate them.

A

A central electrode surrounded by 4-6 peripheral electrodes.

Great as current can be more localised, but you get more activation of the skin, and not as much of the brain itself.

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16
Q

What is the theory of neuron polarisation by tDCS?

A
  • tDCS almost certainly changes the efficiency of the synapses themselves, and still modulates the excitability of neurons too.
  • direct current produces bimodal polarisation
  • synaptic efficacy is modulated with somatic polarisation
  • different levels of polarisation in different parts of the neuron.
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17
Q

What does anodal stimulation inhibit?

A

Anodal stimulation inhibits the inhibitory neurotransmitter, GABA. The net effect is therefore excitatory.

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18
Q

What does cathodal stimulation inhibit?

A

Cathodal stimulation inhibits the excitatory neurotransmitter, glutamate. The net effect is inhibitory.

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19
Q

What did Galea et al., (2011) find about the role of the cerebellum and motor cortex during adaptive learning?

A

Higher rate of learning following only anodal tDCS stimulation of the cerebellum

Greater memory retention following only anodal tDCS stimulation of the motor cortex.

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20
Q

Describe the relationship between the frequency of stimulation and size of polarisation when using tACS.

A

Lower frequency stimulations lead to bigger polarisations.

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21
Q

30 minutes of tACS over 5 days does what?

A

Increases alpha wave activity (8-12hz) which aids mental alertness, coordination, calmness, mind/body integration and learning.

Crucially, alpha activity plays a role in information processing linked to the suppression and selection of attention.

22
Q

What is alpha activity associated with?

A

Information processing linked to the suppression and selection of attention

23
Q

What is beta activity associated with?

A

Motor control. Boosting beta activity will slow movements

24
Q

What are phosphenes?

A

Illusions/flashes of light

25
Q

What are the physiological effects of tACS?

A
  • 5 minutes of 10hz of tACS over M1 enhances motor learning, and causes a change in cortical excitability.
  • tACS over V1 induces phosphenes.
26
Q

Which electrodes are stimulated in tRNS?

A

Both. E.g. useful if you want to stimulate two areas/both hemispheres at once.

27
Q

What is the current delivered by tACS?

A

Biphasic, sinusoidal.

28
Q

What does TMS stand for and what does it do?

A

Transcranial magnetic stimulation. Very different type of stimulation to tDCS, tACS and tRNS.

Properly interferes with brain functioning as soon as it is applied, by directly inducing a current in the brain without having to penetrate the body itself.

29
Q

How does TMS work?

A

Current induced in a coil creates a magnetic field. This magnetic field can stimulate and induce a current in a second coil, or in this context, in a neuron.

30
Q

Why are figure of 8 coils used in TMS?

A

It localises the effect/current, enabling a more specific area to be targeted (than tDCS, etc at least)

31
Q

Which neurons are activated when TMS is applied to M1?

A

Upper motor/corticospinal neurons in the motor cortex

32
Q

How much time elapses between the TMS stimulation of M1 and movement of the related muscle?

A

20ms.

33
Q

What does MEP stand for?

A

Magnetic evoked potential

34
Q

How can the effect of TMS over M1 be measured?

A

Activation of muscles as a representation of MEPs.

35
Q

What are the 3 main TMS protocols?

A
  1. Single pulse
  2. Paired stimulation
  3. Repetitive stimulation (rTMS)
36
Q

What do single pulse protocols refer to in TMS?

A

Neural firing, used to measure:

  • state of the corticospinal tract (original purpose)
  • brain mapping studies (i.e. map of M1)
  • evoked movement/sensation

To cause interference::
- virtual lesions/neural noise which temporarily prevents a certain function, but induces no lasting damage.

37
Q

What do paired stimulation protocols refer to in TMS?

A

Two separate coils in two separate regions of the brain, which allow you to measure functional connectivity.

  • Paired pulse (intra-cortical and cortico-cortical connectivity)
  • Paired associative stimulation (change in functional strength)
38
Q

What does rTMS stand for?

A

Repetitive transcranial magnetic stimulation

39
Q

What do rTMS protocols refer to?

A

Long trains of stimulation

  • cortical depression/enhancement
  • long term cortical reorganisation
40
Q

How would you map out the visual cortex?

A

Induce phosphenes and then get participants to draw out where in their visual environment they saw it.

41
Q

At what time period does the visual cortex process visual stimuli? How do we know?

A

Between 60 and 120 ms.

Studies using TMS over the occipital cortex to induce changes in visual perception at different intervals after a stimulus is shown. Such studies find no difference in visual performance when TMS is applied between 0-60 and 120-200ms after the stimulus presentation, but find large deficits in performance when it is applied between 60-120ms after.

42
Q

Describe interference protocols used by rTMS.

A
  • Stimulating at a low rate (1Hz) causes long-term inhibition of the target tissue.
  • Higher rates (5-20Hz) excites the tissue, lasts at least an hour after the stimulation (also long term).
  • virtual lesions. No long term effect.
43
Q

How can rTMS be used to show modulation of cortical excitability?

A

Stimulation of the motor cortex. Measure size of increase in MEP, and decrease in MEP when motor cortex is depressed.

Slow rTMS for 25 minutes would depress activity by almost half. Gradually increases up to 45 minutes, back to its previous level.

44
Q

What is the inter-hemispheric imbalance after stroke?

A

Typically, both the hemispheres inhibit each other.

Post stroke, if one of the hemispheres are damaged, it will exert less inhibition on the other. Leads to greater inhibition of the affected hemisphere by the intact hemisphere, further shutting it down.

Feng et al., (2013)

45
Q

How can the inter-hemispheric imbalance be restored?

A
  • Anodal stimulation of the affected hemisphere.
  • Cathodal stimulation of the intact hemisphere
  • Both
46
Q

Does bihemispheric stimulation work in reducing hemispheric imbalance?

A

Meta analsysis of 26 studies by Elsner et al., (2017) shows:

  • no effect of sham stimulation
  • cathodal tDCS seems slightly more effective in improving activities of daily life (ADL) than physical rehab, and much more effective than anodal stimulation.
  • tDCS did not change secondary measures of performance.
47
Q

What did Hao et al., (2013) find about the use of rTMS in balancing inter-hemispheric imbalances post stroke?

A

No evidence that TMS is effective, long term, on the balancing of the hemispheres post-stroke.

48
Q

Does tDCS work in the treatment of PD?

A

Benninger et al., (2010):

Anodal tDCS applied to the motor cortex and PFC improved gait by same measures for a short time, and improved bradykinesia in both on and off states (medication) for over 3 months.

No difference in UPDRS, reaction time physical and mental well being, and self assessed mobility.

49
Q

What did Goodwill et al., (2017) find about the effect of rTMS and TES on PD?

A

Overall positive effect of rTMS and TES on the motor, but not cognitive, functions in PD

50
Q

Why has stimulation of the cerebellum become the potential target of treatment for disorders such as Schizophrenia, bipolar disorder, depression anxiety and OCD, when they are not directly caused by cerebellar deficits?

A

The cerebellum has widespread connections to other brain areas.

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