Brain Stimulation

Question 1

Explain the meaning of: tDCS, tACS, tRNS

Answer 1

transcranial direct current (tDCS), alternating current (tACS) and random noise stimulation (tRNS)

Question 2

tDCS directly induces action potentials. Yes/No

Answer 2

Not directly - subthreshold modulations of the membrane potentials affect/bias spontaneous neural activity. Additional mechanisms may be transient changes in receptor sensitivity, neurotransmitter concentration etc.

Question 3

A type of cell polarized best by tDCS

Answer 3

Layer-V pyramidal

Question 4

Differences between cathodal and anodal tDCS stimulation

Answer 4

cathodal - dendrites depolarized, soma hyperpolarized -> inhibitory effect

anodal - dendrites hyperpolarized, soma depolarized -> excitatory effect

Question 5

Conventional tDCS is non-focal and induces a broadly distributed electric field. Yes/No

Answer 5

Yes, for a more focal stimulation larger nr of electrodes can be used (HD-tDCS)

Question 6

tES method to entrain brain oscillations (alpha or theta waves etc)

Answer 6

tACS

Question 7

Which way does the TMS induced current in brain tissue flow?

Answer 7

Parallel to current flow in coil, with reversed direction. TMS causes action potentials in axons that run parallel to the induced electric current

Question 8

What is the mechanism of TMS effect on motor pathways?

Answer 8

1. above threshold TMS pulse causes repetitive wavelike responses in descending motor pathways
2. Travelling to spinal motor neurons they cause transsynaptic activity leading to excitatory postsynaptic potentials (EPSP). The depolarizing effect of these EPSPs adds up and causes action potentials once a threshold is reached.
3. The action potential travels along the peripheral motor axons to the muscle and may be picked up as a summed potential (superposition of many action potentials)

Question 9

There are two kinds of TMS protocols with different effects

Answer 9

excitatory/inhibitory: direct simultaneous effects (online) - single-pulse, double-pulse, burst etc

plasticity inducing: aftereffects (offline) - continuous repetitive, patterned