TMS

Question 1

What is TMS?

Answer 1

• stands for transmagnetic stimulation
• able to temporary de- or activate specific cortical areas using magnetic fieldS
• figure-eight shaped coil generates magnetic field- can be thought of as inducing noise in affected area which disrupts normal function
• both high, continuous administration and low, repeated administration is possible

Question 2

Why is TMS so exciting?

Answer 2

• TMS can have both inhibitory effects through continuous, high-frequency administration
• can be excitatory through intermittent, low-frequency administration

—> reminiscent of long-term potential and long-term depression as recorded in hippocampus in animal models
—> inhibitory effects create momentary virtual lesions that can be reversed
—> better statistical power because it allows for within-subject design
—> excitatory effects have clinical applications

Question 3

Evaluating TMS - Pros

Answer 3

• fMRI scans can be done before TMS sessions to identify target region
• different shapes and sizes of coils available
• as any cogn neuro method, it is used to understand the brain at a much broader level than cellular or molecular neuro aim to do
• BUT can confirm previous correlational findings and make causal inferences about involvements of an area
• outstanding spatio-temporal resolution
• can be combined with other cogn neuro methods
• more precise than natural lesions
• can use healthy brains

Question 4

Evaluating TMS - cons

Answer 4

Despite relatively good specificity, there is evidence to question whether one can fully activate or deactivate the brain region

• -> in fact, both LF and HF may show mixed inhibition and excitatory effects
• -> highly varying effects between individuals (different networks may be recruited between people, different populations may be more easy to activate at different times)
• excitatory effects of TMS may not actually be excitatory in the sense of releasing excitatory NT, but rather may be decreasing the release of GABA

Question 5

Clinical Applications

Answer 5

Literature review analyzed efficacy

• definite effect for HF rTMS: analgesic effect (motor cortex), antidepressant DLPFC)
• probable effect: LF on DLPFC for depression, HF on DLFPC for SCZ, LF in chronic stroke
• possible: LF in tinnitus and auditory hallucinations
• -> long-term effects proportional to number of sessions

Question 6

Specific Example: Parkinsons Disease

Answer 6

• extensive research on TMS in motor cortex because easy to stimulate
• LF inconclusive on improving symptoms

HF support efficacy in M1 for PD

• global improvements in motor scores
• may increase DA
• repeated bilateral sessions most effects

BUT clinical effects rather modest –> substantial improvements to technique and protocol are needed

Question 7

General Limitations

Answer 7

• may not be able to fully differentiate between activation and de-activation
• can only target cortical areas —> limited in research and clinical applications
• previous neuronal activity can influence plastic changes associated with TMS

—> impact of drugs, and disease-related plasticity changes
—> need to be taken into account when interpreting clinical effects of treatment protocols