Week 3 - Brain Stimulation Flashcards
What are some non-invasive forms of brain stimulation?
Transcranial Magnetic Stimulation (TMS)
Transcranial Direct Current Stimulation (tDCS)
Why is transcranial magnetic stimulation (TMS) so useful?
Non-invasive
Excellent temporal specifity
Ok spatial specificity (intensity-dependent - coil selection important)
Can be used in conjunction with motor tasks/cognitive tasks to actually explore the neural mechanisms of behaviour
What adverse events have been reported for transcranial magnetic stimulation?
Mild transient headache
light headedness/fainting
Nausea
Seizure
What are the uses of transcranial magnetic stimulation?
Assessment
- corticospinal exciability
- Intracortical inhibition
- Connectivity
Disruption
Modulation
How is average corticospinal excitability calculated via single-pulse TMS?
MEP (mV) averaged over a number of stimulations
What is the principle of Electromagnetic induction by Michael Faraday 1831?
Production of a voltage across an electrical conductor due to its dynamic interaction with a magnetic field
What happens following a stroke?
Ipsilesional hemisphere is reduced
What further suppresses the ipsilesional cortext?
Interhemispheric inhibition (via the corpus callosum) from the contralesional to ipsilesional hemisphere
What did Fregni et al find in a small study of 15 chronic stroke patients?
Daily low frequency of rTMS to the contralesional hemisphere for 5 days resulted in reduced excitability of the contralesional M1
Improves paretic hand function compared to control group, with effects lasting up to 2 weeks after completion of the treatment
What did Ackerly et al find in a study of stroke patients?
A single session of cTBS suppressing the contralesional hemisphere resulted in a deterioration in paretic hand function
suggests that the contralesional hemisphere may play a role in the recovery of hand function after stroke in some patients, possibly via ipsilateral descending pathways
How are motor symptoms of Parkinsons treated with TMS?
HF (high freq), rTMS to SMA or M1
How does TMS treat depression associated with parkinsons disease?
rTMS to DLPFC (dorsal lateral prefrontal. cortex)
What is dystonia?
Problems with loss of inhibition or excessive plasticity
How can dystonia be treated with TMS?
LF (low frequency) rTMS (or cTBS) to try and reset levels of inhibition and counteract excessive plasticity (M1, PMC, SMA, S1, Cbm)
Is TMS effective for treating dystonia?
Insufficient evidence to recommend rTMS as a therapeutic tool
Is TMS effective in treating motor symptoms of parkinsons disease?
Not strong evidence for treatment of motor symptoms
Is TMS effective in treating the depression associated with parkinsons disease?
Probable efficacy in treating depression associated with PD
What area of the brain is involved in movement preparation and organisation of self-initiated movements?
SMA (supplementary motor area)
What brain regions can be targetted by TMS to reduce tic severity of people with Tourettes?
Some evidence for LF (low frequency) rTMS to SMA reduces tic severity
What is a much better alternative than ECT when treating treatment-resistant Major Depressive Disorder?
TMS
What are the side effect of Transcranial Direct Current Stimulation?
Tingling, itching redness
What is the typical time of stimulation for tDCS?
20 min
What is transcranial direct current stimulation (tDCS)
Induction of LTP-like of LTD-like plasticity through
1) shifts in the membrane potential of underlying tissue
2) changes in synaptic-activity that mimic LTP and LTD processes
How is tDCS different from TMS?
tDCS and other electrical current stimulations can only be used to induce neuroplasticity - they do not meaure excitability or inhibition in regions or circuits
What is used to assess the physiological outcome of tDCS (e.g increase in excitability of M1) or look at the behavioural effect of tDCS (clinical, cognitive, affect etc)
TMS (suprathreshold stimulation)
The volume of grey matter in the brain steadily declines across the life span. What is this a result of?
Not a result of cell death,
but lower synaptic densities in older adults
What needs to be established before we can start to investigate the highly complex and multifaceted relationships between the changes in cortical excitability and behaviour?
The fundamentals of non motor tDCS need to be established
What is electron doping?
The use of brain stimulation (mainly electrical stimulation) to enhance cognitive (and motor) performance in the healthy population
TMS has primarily studied what brain area?
Primary motor cortex (M1)
As the intensity of TMS declines quickly with distance from the coil, what is usually assumed?
That neural stimulation is limited to the cortex and superficial subcortical white matter
What happens when M1 is stimulated by TMS?
A motor provoked potential (MEP)
Produces a descending activity in the corticospinal pathway that activates muscles on the opposite side of the body and produces a physical twitch
What is the purpose of delivering pairs of pulses rather than a single pulse?
To study intracortical inhibitory and excitatory circuits
How can TMS assess inputs to M1 from other areas?
By observing how the MEP (motor provoked potential) is modulated by a preceding stimulus, either a magnetic pulse applies over a different cortical area or a stimulus activating afferents from various sensory modalities
What protocols can induce long-term changes in cortical excitability that are a result of synaptic plasticity?
Repetitive TMS in the form of short or long trains, regular or patterned or associated with diverse cortical or sensory stimulation
What is the rational use of non-invasive brain stimulation (TMS)?
Provide additional benefit to conventional treatment
How does TMS induce long term potentiation?
Short period of high-frequency repetitive stimulations
How does TMS induce long-term depression?
Low frequency stimulation
How many rTMS sessions are required for depression remission?
up to 6 weeks
at least 20-30 sessions
