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TECHNIQUES > tms > Flashcards

tms Flashcards

1
Q

What principle is TMS based on?

A

the principle of electromagnetic inductions

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2
Q

TMS basics what is happening at the level of the coil

A
  • Electricity flows through the coil
  • induces a magnetic field
  • (This magnetic field induces a transient magnetic field that affects the membrane potential of neurons underneath) the
  • field is capable of inducing action potentials of neurons underneath
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3
Q

TMS - does it have excitatory or inhibitory effects

A

both - it can both elicit activity and interfere with ongoing electrical activity (virtual lesion)

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4
Q

what are the different types of TMS

A
  • single pulse TMS
  • repetitive pulse (rTMS)
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5
Q

single and repetitive - online vs offline effects?

A
  • single pulse - just one pulse - very transient process. online.
  • repetitive pulse TMS - online and offline.
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6
Q

online effect

A

Looking at behavioural effects WHILE the pulse is being delivered.

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7
Q

repetative pulse stimulation

A

more than one pulse a second.

  • up to many pulses
  • 100Hz would be 100 pulses a second
  • online - looking at current effects of the pulse
  • offline - looking at after-effects of the pulse
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8
Q

rTMS offline effects - what effects the stimulation after-effects

A

the frequency at which you stimulate n

  • low freq repetitive TMS (< 1HZ) - decreases cortical excitability
  • high freq rTMS (> 5Hz) - increases cortical excitability

the effecrts ofTMS depend upon the frequency at which you stimulate

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9
Q

Why was theta burst stimulation ( TBS) created. what are the subtypes?

A

to enhance the after-effects (longer duration) of repetitive TMS

  • Intermittent TBS - facilitates MEP - increase cortical excitability
  • continuous TBS - inhibits MEP - decrease cortical excitability
  • intermeiate TBS - unaffects MEP

MEP is the motor evoked threshold - how much activity is needed to elicit a behaviour.

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10
Q

whats the difference between TMS and TDCS?

A
  • TMS - electromagnetic induction
  • TDCS - direct electrical stimulation - but with very very weak currents (~1mA)
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11
Q

TDCS - how is the weak current delivered?

A

the weak current is delivered to the cortex using 2 electrodes (damp sponges) placed on the scalp

  • anode - red - current enter through anode
  • cathode - blue. - travels through any cortex it goes through and exits through the cathode

so this means wif you change these round you are changing which neurons the current passes through.

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12
Q

how does TMS look vs TDCS

A

TMS

  • swimming cap placed on the head with red spot somewhere
  • pair red spot with the mid-point of the coil
  • deliver pulse

TDCS

  • two electrodes placed on scalp - anode and cathode
  • held in place with adjustable band
  • electrode leads attached to stimulator
  • stimulator - lightweight electronic box
  • very portable
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13
Q

TDCS - what convection is it

A

conduct the behavioural task you are interested in e.g., visual search task either

  • during stimulation
  • and/or immediately after it

Could have stimulation parameter that lasts 15 minutes. might leave it to start having an effect after 5 minutes then test n the remaining 10.

or you could stimulate for 15 minutes and not do anything then as soon as stimulation ends go - right now do the task

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14
Q

TDCS electrods - sizes

A

large (7x5 cm)

small ( 3x3cm)

so they aren’t particularly small electrodes

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15
Q

What does the efficacy ofTDCS depend on?

A

different parameters

  • current density - this determines the ELECTRICAL field strength
  • the strength of the field is dependent on both - the stimulation density chosen and the size of the electrode (size of area being stimulated)

so higher intensity + smaller electrode size will increase the ELECTRICAL field density

small intensity + large electrode - you spread the stimulation across large area

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16
Q

differences in the lasting effects of excitablity with TMS and TDCS

A

TMS - 1 pulse effects activity, soon as stimulation stops activity reverts back to normal

TDCS - induces longer lasting changes in excitability (depending on stimulation parameters)

  • might return back to normal if TDCS is applied for less than 10 mins
  • if it’s applied for 15 mins - excitability changes that last up to 90 minutes
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17
Q

two types of TDCS

A

Anodal stimulation

  • anode covers a region of interest
  • enhances cortical excitability

cathode stimulation

  • cathode over region of interest
  • decrease cortical excitability
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18
Q

describe a set up of anodal stimulation

A
  • if we were interested in the right posterior parietal cortex - place the anode there
  • place cathode over the contralateral subra-orbital region. (the forhead)

if anode is over the region of interest it should enhance cortical excitability here.

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19
Q

Why does placing the anode over the region of interest INCREASE cortical excitability?

A

Excitatory (anodal TDCS) causes locally reduced GABA

Stagg et al., (2009)

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20
Q

Why does placing the cathode over the region of interest DECREASE cortical excitability?

A
  • Inhibitory (cathodal) stimulation causes reduced glutaminergic neural activity
  • with highly correlated reduction in GABA

Stagg et al., 2009

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21
Q

What did Staggs paper find out when looking at the anodal and cathodal stimulation underlying mechanisms?

A
  • used magnetic resonance spectroscopy to look at the effect of TDCS on NT’s
  • found anodal TDCS caused locally reduced GABA
  • while cathodal stimulation reduced glutaminergic activity
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22
Q

Other than the reduction of GABA/Glutaminergic NT’s what other things could modulate the effects of TDCS?

A

some evidence that TDCS effects are modulated by glial cells.

  • Glial cells don’t have an action potential or anything
  • they are structural cells within the brain that have many important functions like functional and nutritional support for neurons

Ruhenonen and Karhu 2012

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23
Q

What things have people argued modulate the effects of TDCS in the brain?

A
  • the reduction of NT’s
  • glial cells
24
Q

Disadvantages of TDCS

A
  • shit spatial resolution - cant tell you wheresomething is happenign in the brain
25
Q

How long does a typical TDCS experiment last for

A

About 15 minutes

  • probably set electrodes up 5 mins before that
  • because you want to let electrodes become body temperature
  • electrodes + saline might initially be cold
  • to improve conductivity you want them to settle
  • less of a problem when on skin but if over someone’ s hair it can be hard to get nice good clean contact between electrode and scalp
  • so leave for 5 mins to produce this nice contact
  • then 15 mins of stimulation
26
Q

if you are delivering TDCS and the stimulator that monitors the stimulation going in says “high impedance” what does this mean?

A

you’ve lost contact in some way, someone might have moved and knocked electrode further away from scalp

OR and what normally happens - is it’s dried out. so to prevent this inject the electrodes with saline syringes to keep the impedence low throughout the 15 mins of stimulation

27
Q

What effects do the reference electrode appear to have?

A

Baudewig et al., 200

  • TDCS and then neuroimaging
  • found the effects of TDCS on cortical excitability are supported by concurrent neuroimaging findings - after cathodal stimulation
  • MRI sees a decrease in activity in areas underlying the electrode.

see a less task-related activation following cathodal stimulation directly under where the electrode was placed

28
Q

are the effects of TDCS restricted to the site of the electrode

A
  • no, they extend to other functionally relevant and widespread areas.
  • target the wider processing loops relevant to task
  • particular strength of the technique - good for questions about network, if you want to investigate the communication between sites
29
Q

how does TDCS help us investigate networks in the brain

A
  • because the effects of TDCS aren’t restricted to the site under the electrode
  • if your’e interested in the communication between sites - networks in the brain TDCS is good for those
  • deliver stimulation to one point in the brain - this then spreads through the network of functionally connected areas
30
Q

Describe 3 studies using TDCS

A
  • lyer et al (2005) - verbal fluency. 2mA stimulation of left PFC. anodal improved while cathodal decreased performance.
  • Fregni et al., (2005) - working memory. left DLPFC anodal stimulation improved performance.
  • Vines et al., (2006) - auditory pitch memory. cathodal stimulation over left supramarginal gyrus had a detrimental effect on performance.
31
Q

What is the basic point of TDCS and TMS?

A
  • functional localisation
  • investigating the contribution of a particular brain area to a particular task
  • and whether that particualar area is involved in the task
32
Q

When would TDCS be prefereable over TMS in cortical functinoal localisation studies

A

if you are interested in sound.

  • tms audible clicking sound would interfere with any task of auditory processing
  • silent TDCS has this advantage

if you’re interested in PFC

  • stimulating this with the TMS coil would just stimulate someones face
  • get huge twitches in the face - periferal nerve side effects
  • so as n do task they would just be twitching their way through it
33
Q

key things about TMS

A
  • transient process
  • limitted to cortical stimulation
  • has somatosensory (tingling) and auditory effects
34
Q

Describe TMS set up

A
  • electrical capacitor stores electrical activity
  • sends this electrical activity to the stimulator
  • stimulator sends pulse to coil
  • current flows round coul producing electromagnetic field of 2 tesla
35
Q

What different types of coil used in TMS

A
  • figure of 8 coil
  • one with different geometry
36
Q

Describe the mechanics of TMS figure of 8 coil

A
  • 2x power in the middle - more focal stimulatio
  • copper inside, good bc it has high heat capacity.
  • as the current flows it generates heat, In the past the coil would burn n scalp if too hot.
  • now theres a built in thermometor that shuts coil off if it gets too hot
  • also copper has good tensile strength
37
Q

Why might someone not decide to use the figure of. 8coil

A
  • if they wanted to stimulate deeper regions
  • the geometry of other coils allow the stimulation to go down the interspheric fissure
38
Q

Why might someone not decide to use the figure of. 8coil

A
  • if they wanted to stimulate deeper regions
  • the geometry of other coils allow the stimulation to go down the interspheric fissure
39
Q

Describe the evolution of TMS

A
  • in the past - single pulse delivered every 4 seconds
  • this is bc after the pulse - a lot of the energy was being lost as heat
  • so we had to wait for capacitor to recharge after each pulse
  • then we found a way to reuse the energy allowing for repetative pulses back to back without the waiting period between
  • led to development of rTMS - quicker stimulation
40
Q

what are the stimulation effects of TMS

A
  • difficult to say bc it depends on a lot of parameters
  • where is stimulated, what parameters are used, current neural activity of the region
  • but in general TMS causes depolarisation of resting neurons - increased likelihood they fire
41
Q

TMS can either elicit activity or interfere with ongoing activity. Describe how.

A
  • if pulse delivered to resting neurons - generates action potential and elicits activity
  • if pulse delivered during ongoing activity - interferes with activity and disrupts performance.
  • this slows responses, increases the number of errors made.
42
Q

Describe how r/TMS might elicit or inhibit activity.

A
  • if pulse delivered to resting neurons - generates action potential and elicits activity
  • if pulse delivered during ongoing activity - interferes with activity and disrupts performance.
  • this slows responses, increases the number of errors made.
43
Q

Are TMS and TBS delivered at similar intensity?

A
  • no
  • TMS is delivered at a higher intensity - 1.3 Tesla
  • TBS is delivered at a lower intensity - 1 Tesla
44
Q

Describe theta burst stimulation

A
  • short bursts but heavily packed
  • burst of 50 Hz! (which is gamma frequency)
  • then repeated bursts of activity are in the theta frequency (5 Hz)
  • this coupling between gamma and theta frequency mirrors what happens in the neocortex during a cognitive task
45
Q

What parameters are used in TBS?

A
  • initiall Hz = __ ?
  • repeated Hz = __ ?

lots of different combinations exist but most people replicate the parameters set by Huang et al., 2004

46
Q

Different types of TBS

A
47
Q

what do we use TMS for?

A
  • functional localisation
  • and timing of neural activity
48
Q

Functional localisation: Visual study. Ellison and Cowey (2006)

A
  • TMS delivered to right lateral occipital cortex (region important for shape discrimination)
  • n did 3 tasks - shape, distance, colour discrimination tasks.
  • TMS slowed the reaction time in the shape discrimination task
  • tells us this regin is important for shape perception
49
Q

Functional localisation: Visual study. Beckers and Zeki (1995)

A
  • motion perception - dots move actoss screen n say which direction they moved in
  • stimulated V1 and v5
  • 60ms (before stim onset) and 100 ms (after stim onset)
  • most interference = TMS to V5 - 10ms and +10ms after stim onset
  • n were 100% accurate, now 50%
  • now we know V5 is crucial for motion perception
50
Q

Functional localisation: Visual attention study. Walsh et al., (1999).

A
  • conjunction task
  • visual search find line that satisfied 2 criteria - orientation and colour
  • requires both serial search and visuo-spatial attention deployment
  • TMS delivered simultaneously with stim onset for 500ms at 10Hz
  • stimulation increased RT by 100ms
51
Q

Functional localisation: Visual attention study. Ellison, Rushworth and Walsh (2003)

A
  • feature search task - 1 feature
  • could just do parrallel search - stim practically jumps out
  • is the R.PPC still involved?
  • NO. TMS had no effect
  • then gave them 2 conjunction tasks - an easy one (solvable by parallel search) and a harder one
  • is the R.PPC involved in both?
  • YES. TMS had an effect
  • meand rPPC detects location of a combination of features, conjunction tasks.
  • findngs support feature detection theory (T and G) that say R.PPC integrates feature and spatial information (finds objects that meet the criteria and locates them)
52
Q

Functional localisation: Visual attention study. Ellison et al., (2004)

A
  • hard feature, easy feature and hard conjunction
  • while stimulating R.PPC and the right superior temporal gyrus
  • TMS to RSTG decreased performance in the hard feature task
  • this area is related to task difficulty
53
Q

Timinng: Movment study. Schluter et ak., (1998)

A
  • task - respond to a stimulus as qiuck as possible
  • stimulate premotor cortex vs motor cortex
  • premotor cortex stim - most interference when stiulated 140ms after stim onset
  • motor cortex stim - most interference when stimulated 220-300ms after stimulus onset
  • gives us insight into the timing of region involvment
  • premotor involved earlier, region probably related to initiation and panning of movment
  • motor = involved later, proobably related to execution of movmnet
54
Q

Timing: language study. Stewart et al., (2001)

A
  • task: say - supracalifragalisticexpyalidocious
  • While TMS delivered to brocas area
  • n cant do it - region related to speech production
55
Q

Investigating the interaction between areas: Ellison, Lane and Schenck (2007)

A
  • explore interactino between R.PPC and V5
  • TMS delivered during task completion - 500ms at 10 Hz
  • Various visual search tasks given: colour/shape conjunction task and mvment conjunction task
  • n press button when believe they see the stimulus
  • results: double dissociation
  • PPC stimulation had big effect on colour/shape task
  • V5 stimulation had big effect on motion task

PART 2

  • now stimulated both areas and give n a motion conjunction task
  • PPC stimulation = no effect
  • V5 stimulation = yes effet
  • V5 and PPC stimulation = massive effect
  • V5 and vertex = yes effect, same as V5 alone
  • so not just V5 paired with something bc - v5+vertex had a normal effect. it was specifically when paired with PPC when it had the biggest effect

why ?

  • because V5 strips motion task bare
  • now a feature search task
  • but we stimulated and impaired v5 so you cant do this anymore and have to serially search the items looking for the conjucted stimulus (PPC job)
  • since PPC also impaired your basically fucked
56
Q

What are the theraputic effects of TMS

A

Approved for the treatment of

  • depression
  • schizophrenia
  • chronic pain
  • neglect
57
Q

Saftey guidlines of TMS

A
  • be careful with intensity and frequency (if using rTMS)

Excusion criteria - both n and experimenter

  • anything in head
  • epilsepsy
  • neurological conditions
  • medication
  • pregnant n
  • hearing loss/tinitus

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