Atskymai

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1. Physical principles. Explain basic mechanisms and what happens in the brain.

By placing a wire on the scalp and passing a powerful and rapidly changing current through it, a magnetic field is produced that penetrates the cranium, virtually unimpeded and relatively painlessly. An eddy current is induced in the brain as a result of this changing magnetic field, and this in turn penetrates the membranes of the neurons, resulting in an action potential or excitatory (or inhibitory) postsynaptic potential. Another important feature is that the magnetic field falls off rapidly with distance from the coil: With a typical 14-cm-diameter round coil, the strength falls by half at a distance of 4 to 5 cm from the coil surface

2. Single pulse and rTMS. What is happening in the brain?

With rTMS there is a risk of inducing a seizure in high frequency rTMS.

3. Monophasic and biphasic

Although both phases of biphasic pulse were capable of activating descending motor output, induced current in the PA direction was more effective in eliciting descending volleys at lower stimulus intensities.

4. Spatial, temporal resolution, coils.

TMS - focal, fast, circular coil, near the center the intensity of the magnet weakens and in the middle there is no intensity.

tES- less focal, weaker than TMS (thus the effects are considered less stronger)

5. D-waves, I-waves. Their hyphothesis.

D waves, representing direct stimulation of the corticospinal axon, as well as I waves that arise from transsynaptic activation of corticospinal neurons. With increasing stimulus intensity, later waves, termed I waves, come to follow the D waves at intervals of approximately 1.5 msec. They are named I1, I2, and I3 waves in the order of their latency.

Because the latencies of I waves are longer than those of D waves, they are considered to arise from transsynaptic activation of pyramidal tract neurons.

With electrical stimulation, the D wave threshold is always lower than that for any I waves

An alternative explanation, which is now generally accepted, is that electrical stimulation excites the corticospinal fibers directly, giving rise to D waves, whereas TMS excites the pyramidal neurons transsynaptically, giving rise to I waves.

6.rTMS protocols, low, high frequency what does it do.

rTMS. Repetetive transcranial magnetic stimulation. Low frequency inhibits brain excitablity (from 0.2 Hz to 1Hz), while high frequency (from 5Hz) enhances brain excitability.

7. TBS. Say it in detail. Numbers would be nice.

3 stimuli using 50Hz frequency with interstimuls interval of 200ms 600 pulses. Intermediate TBS (5 s train repeated every 15s for a total of 110s), intermittent TBS (2s train repeated every 10s for 190 s), continous TBS (40s train of interrupted TBS 600pulses).

8. Problems of controlling specificities, control conditions.

Control sites, control conditions (stimulation frequency, stimulation intensity, stimulation duration effect, duration of stimulation effect)

Discomfort, for TMS it is technically hard to have sham conditions.

General arousal due to TMS usage, auditory clicks, coil vibrations.

When TMS is delivered over the motor cortex while the subjects maintain voluntary muscle contraction, a pause in ongoing EMG activities follows the evoked CMAP, which is called the silent period.

9. TMS with imaging. Elaborate additional values to MRI.

TMS could affect in remote brain structures.

Problems: attach coil, magnetic stimulator has to be shielded or used in another room to not interfere with MRI. Long connecting cables (you loose power with them). Researchers thus have to rise the motor threshold intensity. You can do experiment with MRI only and then TMS with MRI.

While EEG and MRI can only identify correlational links between brain and behavior, with the help of TMS it can have more causational results.

TMS and EEG: TMS compatible EEG equipment can work in very high, time-varying magnetic fields without saturation. Couple of technical answers:

1. TMS compatibility with gain-control and a sample-and-hold circuit that locks the EEG signal for several miliseconds immediately post-TMS.

2. Slew rate limited preamplifiers to prevent saturation during TMS pulse, allowing continous data recording and resulting in a short-lasting effects.

Modelling of the induced current density. It would allow of exact "dose" calculation (strenght of the field induced in different brain areas).

10.Advance research design. Know that you can have two coils.

Online, offline studies, with two coils you are able to elicit SICI (short cortical inhibition or facilitation), depending on the research question and the time interval between pulses.

11. Entrainment. Two studies are mentioned and you have to know a bit of them. Elaborate about differences.

12. Romei study using tACS and TMS for entrainment

5 pulses at 3 different frequencies: 5Hz, 10Hz, 20 HZ. NIne blocks of entrainment. Occipital cortex (R and L), Parietal cortex (R and L). Sham normalization, subtracting mean rate of sham from the real condition mean rate. 10 Hz contralateraly impaired stimulus, ipsilaterally enhanced detection compared to other conditions. Alpha inhibition theory, because it suppresses contralateral detection. Enhancement has some sort of transcallosal network effects. Two other frequencies do not work because of different phases 5hz too long, 20 hz too short and anti-phasic.

13. Differences in entrainment between tACS and TMS - TMS is more focal.

TMS - phase reset. excites neurons directly. It is possible to use it with EEG

tACS - modulates the spontaneous firing rate of neurons through a shift of the cell resting membrane potential. Can only entrain cortical oscillators operating close to the driving frequency. You can work with 0 degree and 180 degree phase differences in more exact timing. technical difficulties in EEG comparison. tACS shows enhancement

1. A null result could mean that the stimulation truly had no effect or that the stimulation was insufficient to affect functioning in the target area.

2. In addition, a null resul may occur if two brain areas participate equally in the specified cognitive task, suca that interfering with only one of them does not result in an overt behavioral change.

3. May arise from compensation during which another brain area takes over the respective function of the directly stimulated region.

14. Simultaneous techniques, static, dynamic artifacts.

Rapidly changing scalp potentials (???), in MRI are susceptible to magnetic field inhomogeneities, images affected 100ms after the pulse, EEG muscle twitches could be visible.

15. Clinical potential, prognostic, example.