But it is? In the survey by Bluhm and colleagues, responses were varied. Some treatments that are thought to involve multiple visits to the doctor’s office are invasive because they affect a person’s period. Others think device-based treatments are less invasive than traditional talk-based therapies, because they don’t require a stranger to tell his or her life story. But others say that what makes TMS so invasive is its impact on the brain.
The effects can spread throughout the brain. In theory, non-invasive forms of brain stimulation are designed to target specific regions, such as those associated with mood. But it’s impossible to pinpoint small areas when you stimulate the brain through the skull, like Nick Davis at Manchester Metropolitan University shown.
And if TMS can help treat symptoms of chronic pain, depression, or Parkinson’s disease, it must elicit some changes in the brain. This could be how the signal molecules are generated, or how brain circuits connect or fire, or perhaps some other mechanism.
And since we still don’t really understand how TMS works, it’s difficult to know how these changes might affect the brain in the long term, if at all.
Is it an invasive treatment if it changes the way a person’s brain works? Maybe it depends on the impact of those changes. We know that “non-invasive” forms of brain stimulation can cause headaches, seizures, and potentially convulsions. Electroconvulsive therapy, which provides a higher dose of electrical stimulation, is designed to trigger seizures and can cause memory loss.
This can be extremely distressing for some people. After all, our memories make us who we are. And this leads to one of the other concerns about brain-altering technologies—the ability to change our personalities. Doctors have noticed that some people with DBS because of Parkinson’s disease have temporary changes in their behavior. For example, they may become more impulsive or irritable.
It is unlikely that the effects of noninvasive stimulation would be as dramatic. But where do we draw the line—what is considered “intrusive”?
That is an important question. Treatments that are considered invasive are often reserved for people who have no other options. They are considered riskier. And the treatments are considered too invasive may never be used, or even studiedaccording to Nir Lipsman, a neurosurgeon at the University of Toronto, and his colleagues.