Brain Stimulation methods

what are the two types of brain stimulation

• transcranial megn etic stimulation ( TMS)

• transcranial direct current stimulation (IDCS)

what is TMS

passing a current through magnetic coil on persons head to induce a magnetic field in the particular area of the scalp, which makes an electrical current in that underlying brain region

what are the acute( short term) effects of tms (2)

• phasic activation of neural networks

• observable motor responses e.g. a twitch

what are prolognued ( longer term) effects of tms ( 2)

• neuroplasticity

• change in neural efficacy leading to LTP or LTD ( long term potentiation/ depression)

what are the 2 main types of TMS coil

• and name an advantage of each

round coil

• simple construction and stable head contact

figure 8 coil

• harder to fit round head but improved efficiency and penetration

TMS can be used for both assessment and treatments.

What are the 2 types of TMS used in assessing brain activity ?

• and does TMS invoke action potentials

• TMS DOES invoke action potential

2 types :

single pulse TMS

• one pulse applied at a time to produce motor evoked response (MEP)and paired pulse

paired pulse TMS

• applying two sequential stimuli of varying intensities seperated by interstimulus interval

• valuable for investigating intra-cortical connections (within brain regions)and inter-cortical connections (between different brain regions)

what are 3 factors of the motor system we can measure with single pulse TMS

1. motor threshold

stimulus intensity causes minimum motor response

2. cortical/ silent period

silence of ongoing volentary emg activity

3. input/output curve

relationship between stimulus size and MEP size

what are the two types of intervention ( treatment) TMS

• repetitive TMS = applying recurring TMS pulses to specific brain region

• theta burst stimulation TMS = pattern of three 50Hz pulse at a 1-5Hz frequency. can be continuous or intermittent.

which type of TMS

(a) cause inhibition

(b) cause excitation

(a) = low frequency repetitive TMS (rTMS) and continuous TBS ( cTBS)

(b) = high frequency rTMS and intermittent TBS(iTBS)

what it tDCS ( transcranial direct current stimulation)

• key points on what it is including what are 4 montages of tDCS

tDCS = using a constant weak electric current to modulate brain regions over which it is applied

• electrical stimulation via positive/ negatvive electrodes

• modifies cortical excitabilitu

• different montages can be applied

4 montages:

anodal
cathodal
bihemispheric
high density

what is meant by the fact that tDCS modifies cortical excitability ( not too important)

anodal tDCS increases the amplitude of EMPs (cathodal reduces)

what factors affect the electrode montage of tDCS (there are 4)

• skin contact area/size

• position of electrodes

• stimulation intensity

• duration

advantages of TMS(name 3)

• not affected by intervening tissue

• more precise stimulation

• leads to long lasting results

advantages tDCS ( name 3)

• portable

• inexpensibe

• easy to use

weakness of TMS ( name 3)

• expensive

• can produce twitching in scalp = discomfort

• complicated to use

weakness of tDCS( name 3)

• affected by intervening tissue

• side effect of itching under electrode

• efficacy of tDCS is mixed . more research needed.

name 5 applications of TMS. explain 3

• assessing neuroplasticity = in patients using constraint induced movement therapy can measure motor region areas pre / post intervention using TMS

• measuring cortical inhibition = measuring the silent period after MEPs. there is a longer period of inhibition due to suppression of cortical excitability

• treating depression = stimulating the dorsolateral pre frontal cortex dampens cortical activity and improves depression

• assessing corticospinal tract integrity

• virtual lesions

name 3 potential applications of tDCS

• enhancing cognitive function

• treatment depression

• improving sensorimotor function

• describe the role of tDCS in enhancing cognitive function

anodal and cathodal tDCS can improve working memory

describe how tDCS could be used to treat depression

tDCS is portable so you could wear it at home
works for unipolar but for bipolar is no different to sham