TMS: Neurocircuitry-Part 2

Considering how important it is, the dorsolateral prefrontal is surprisingly small. And because everybody's brain is a little different, its precise location can vary slightly from one person to the next. But in TMS, precise location of the stimulus is essential along with intensity, frequency, and duration. By altering these parameters in different ways, TMS can be used for different purposes.


For example, fast, excitatory TMS applied to the left dorsolateral prefrontal cortex has been approved by the FDA as a treatment for depression, but slow, inhibitory TMS applied to the same region has no effect on mood. On the other hand, recent studies have shown that fast, excitatory TMS applied to the right dorsolateral prefrontal cortex is an effective treatment for depression and slow, inhibitory TMS once again appears to be an effective treatment for depression.


TMS has been used experimentally to treat refractory epilepsy. In this situation, slow, inhibitory TMS is applied directly to the epileptogenic focus, the site in the brain where the seizure originates. When this is done repeatedly, over time, it has the effect of quieting down the focus.


TMS has also been used experimentally to aid in recovery from stroke, but here a different approach is used. Fast, excitatory TMS can be applied directly to the site of the lesion in an effort to stimulate damaged brain cells to function more effectively. But better results come from stimulating the corresponding site of the opposite, undamaged hemisphere. When this is done repeatedly, over time, it has the effect of stimulating neuroplasticity and regeneration at the site of the lesion.


And this is really the essence of how TMS works--by stimulating neuroplasticity.


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