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Bursts of Low-intensity Ultrasound Make Neurons Fire.

A new way to stimulate the brain through the skull could lead to better targeted therapies.

2 min read
Bursts of Low-intensity Ultrasound Make Neurons Fire.

Neuroscientists are well accustomed to making neurons fire artificially by shocking them and doping them. Indeed it's the backbone of most neurological therapies. Now, it seems, we can do it with just sound.

Bioengineers at Arizona State University published an article in Neuron today (it's free online) in which they demonstrate the ability to stimulate neuronal action potentials (electrical impulses) by applying bursts of low-intensity ultrasound to the mouse brain. Other people have shown that this is possible to do in brain tissue, but the Arizona lab claims to be the first to make it work through the skull in a live animal.

If such a technique is to become therapeutically viable it will have fierce competition from another stimulation strategy that excites neurons through the skull with either direct current or electromagnetic induction (called tDCS and rTMS respectively). These two approaches have spawned a veritable deluge of research, raising hopes of alleviating migraine pain, depression, and attention deficit disorder, to name just a few. Despite a lot of encouraging results, rTMS and tDCS have pretty terrible spatial resolution and this is precisely where ultrasonic stimulation may be able to compete and contribute.

In the experiments published today, the researchers looked at spatial resolution in two different ways. First they stimulated areas of the brain that control movement and found that they could isolate specific muscles. Point pulses of ultrasound at one part of the motor cortex and the paw twitches, move it slightly and the tail jerks. This alone is more precision than has been shown with electrical stimulation. (There's a link to a movie for those who can stomach research on restrained mice).

But the group went further and analyzed the biochemistry of the brains to see exactly what parts of the tissue had been stimulated. Their results suggest that ultrasound can be used at a resolution that is about 5 times better than rTMS. They also estimate that they could successfully use 0.5 MHz of ultrasound to stimulate brain regions that are 1 millimeter wide and less.

However, it's not as clean as all that. The sound waves seem to reflect in some instances and can stimulate the tissue unpredictably.

As of yet, there is no solid hypothesis to explain how the ultrasonic waves cause neurons to fire. The most convincing theory is that it produces enough mechanical stress on ion channels to open them. Normally these channels remain gated until the electrical potential across the neuron's membrane changes enough to fling them suddenly open and initiate the cascade effect we call an action potential.

Whatever the mechanism, the side effects on the cell seem to be minimal. Basic tests for cellular death showed no increases after applying the ultrasound.

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Are You Ready for Workplace Brain Scanning?

Extracting and using brain data will make workers happier and more productive, backers say

11 min read
A photo collage showing a man wearing a eeg headset while looking at a computer screen.
Nadia Radic

Get ready: Neurotechnology is coming to the workplace. Neural sensors are now reliable and affordable enough to support commercial pilot projects that extract productivity-enhancing data from workers’ brains. These projects aren’t confined to specialized workplaces; they’re also happening in offices, factories, farms, and airports. The companies and people behind these neurotech devices are certain that they will improve our lives. But there are serious questions about whether work should be organized around certain functions of the brain, rather than the person as a whole.

To be clear, the kind of neurotech that’s currently available is nowhere close to reading minds. Sensors detect electrical activity across different areas of the brain, and the patterns in that activity can be broadly correlated with different feelings or physiological responses, such as stress, focus, or a reaction to external stimuli. These data can be exploited to make workers more efficient—and, proponents of the technology say, to make them happier. Two of the most interesting innovators in this field are the Israel-based startup InnerEye, which aims to give workers superhuman abilities, and Emotiv, a Silicon Valley neurotech company that’s bringing a brain-tracking wearable to office workers, including those working remotely.

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