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TMS and fMRI

Remote effects of TMS:

1. Applying TMS to one region can affect activity in remote cortical areas with high spatial specificity, supporting the notion that TMS may influence interconnected brain regions.

2. Confirm that remote BOLD effects can be very different for different sites considered to be within the same overall network.

TMS and fMRI might be means to visualize task-specific brain networks of functional connectivity. Using fMRI before and after TMS we could show effective brain connectivity changes.

TMS is context dependent. And it was shown by EEG studies. It was found for task specific effects.

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.

tES: heating of the electrodes, effect on the image quality, possibility to detect artifacts due to stimulation,

The after-effects of tES dominantly depend on the stimulation parameters, including the stimulation duration, the current density, the electrode size, the current density, the type of current, the timing of the stimulation, and the electrode montage.

TMS and EEG

TMS in sleeping patients. Neural responses are not contaminated by reactions that may result from becoming aware of the stimulation.

Combination of TMS and EEG dissociates effective connectivity (causal interactions) from functional connectivity.

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.

Event related potentials obtained through EEG independently from TMS can be used to identify the time-window during which a given area is activated during performance of a cognitive task. It gives information when an area should be stimulated in order to investigate causal structure-function relationships.

It is thus possible to combine precise timing of TMS with the high temporal resolution of EEG to disentangle the activation sequence of various cortical areas and their causal roles in the execution of cognitive tasks.

TMS EEG approaches:

1. Inductive. Measurements to assses cortical reactivity and connectivity. Can be used to explore effective TMS parameters.

2. Interactive. Which explores when, where nad how TMS affects a functional network during a cognitive task. Identify cortical areas responsible for a given task.

3. Rhytmic. which uses TMS to interact with oscillatory brain activity in order to study causal relationships between rhytms and perceptual, motor, cognitive processes.

Problems:

1. May induce artifacts which will be visible in the EEG.

2. May induce non-specific or indirect responses which may influence the EEG recording

All 3 of them

Thus the simultaneous use of all three methods would allow studying fast, spatially accurate, and distributed causal interactions in the perturbed system and its functional revelance for intact behavior.