Brain stimulation might be more invasive than we think

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Today, there are lots of neurotechnologies that can read what's going on in our brains, modify the way they function, and change the wiring.

This is the case for plenty of treatments that are considered noninvasive" because they act from outside the brain. But if we can reach into a person's mind, even without piercing the skull, how noninvasive is the technology really?

It's a question I've been mulling over, partly because I've just started reading The Battle for Your Brain by Nita Farahany, a law and philosophy professor at Duke University in Durham, North Carolina. Farahany's research focuses on the ethical and legal challenges that new technologies might pose for society.

In her book, Farahany covers the potential impacts of technologies that allow us to peek inside the minds of others. Neuroscientists have already used brain imaging techniques to try to detect a person's thoughts and political inclinations, or predict whether prisoners are likely to reoffend. It sounds pretty invasive to me.

There are different ways to define invasiveness, after all, as Robyn Bluhm at Michigan State and colleagues found when they asked people who have undergone treatments that target their brain activity, as well as psychiatrists and other members of the public.

Typically, in the medical sense, invasive treatments are those that involve some kind of incision in the skin. Deep brain stimulation is an obvious example. The procedure involves implanting electrodes deep into the brain to stimulate neurons and control the way brain regions fire.

For a story published last week, I spoke to a man who volunteered to have 14 electrodes implanted into his brain to understand and treat his depression. He underwent brain surgery, and was awake while doctors probed his brain to find the sweet spot" to place one of these electrodes.

For the 10 days he was in hospital, the man (who didn't want to be identified in the piece) had wires coming out of his brain, his head wrapped up in a bandage. It was undoubtedly an invasive procedure.

Before he signed up, the man had tried plenty of other treatments, including transcranial magnetic stimulation (TMS). This involves passing a device shaped like a figure 8 over a person's head to deliver a magnetic pulse to parts of the brain and to interfere with its activity. TMS is typically considered noninvasive.

But is it? In Bluhm and colleagues' survey, responses varied. Some thought treatments that involve multiple trips to the doctor's office are invasive because they impinge on a person's time. Others thought treatments that rely on devices are less invasive than traditional talking-based therapies, because they don't require regaling a stranger with one's life story. But others said that what made TMS invasive was its impact on the brain.

The effects can spread throughout the brain. In theory, noninvasive forms of brain stimulation are designed to target specific regions, such as those involved with mood. But it's impossible to pinpoint tiny areas when you're stimulating the brain through the skull, as Nick Davis at Manchester Metropolitan University points out.

And if TMS can help treat the symptoms of chronic pain, depression, or Parkinson's disease, then it must be eliciting some sort of change in the brain. This might be in the way signaling molecules are produced, or the way brain circuits connect or fire, or perhaps some other mechanism.

And given that we still don't really understand how TMS works, it's difficult to know how, if at all, these changes might affect the brain in the long term.

Is a treatment invasive if it changes the way a person's brain works? Perhaps it depends on the impact of those changes. We know that noninvasive" forms of brain stimulation can cause headaches, twitches, and potentially seizures. Electroconvulsive therapy, which delivers a higher dose of electrical stimulation, is designed to trigger a seizure and can cause memory loss.

This can be extremely distressing for some people. After all, our memories make us who we are. And this gets at one of the other concerns about brain-modifying technologies-the potential to change our personalities. Doctors have noticed that some people who have DBS for Parkinson's disease do experience temporary changes in their behavior. They might become more impulsive or more irritable, for example.

It's unlikely that the effects of noninvasive stimulation will be anywhere near as dramatic as that. But where do we draw the line-what counts as invasive"?

It is an important question. Treatments that are considered invasive are generally reserved for people who have no other options. They are seen as riskier. And treatments that are considered too invasive might not ever be used, or even researched, according to Nir Lipsman, a neurosurgeon based at the University of Toronto, and his colleagues.

Funnily enough, treatments that are considered to be more invasive might be more effective, just because of the expectation that they will work. That's probably why placebo injections are more effective than placebo pills, as Bluhm and colleagues point out. At the same time, we run the risk of overlooking potential risks associated with treatments that are considered noninvasive.

To read more about neurotechnologies, check out these stories from Tech Review's archive:

TMS can change the way people make moral judgments, according to research carried out in 2010. The researchers behind the work think that the stimulation interfered with volunteers' ability to interpret the intentions of other people, as Anne Trafton wrote.

A noninvasive form of brain stimulation can improve the memory of older people. The technique, called transcranial alternating current stimulation, can be adapted to boost either long-term or short-term memory, and the benefits appear to last for at least a month, as I reported in August.

A more invasive approach uses electrodes implanted in the brain to mimic how healthy brains make memories. This memory prosthesis" might help people with brain damage, as I reported in September.

In 2018, neuroscientists used TMS to pass information from brain signals between three people, allowing them to collaborate on a Tetris-like game. The BrainNet" was described as a social network of brains."

Noninvasive brain electrodes are being used to look for signs of consciousness in people who are in a state of unresponsive wakefulness, as Russ Juskalian reported last year.

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