Korva is a scroll of the internet’s best ideas.
Getting Genes In
Researchers already tickle neurons this way in animals. They put in a gene the neurons do not normally express, usually one for a channel that comes from algae or other tiny non-human organisms. A local injection works but means breaching the skull, so many labs inject an adeno-associated virus instead, which stably expresses genes in the cell types they choose by using specific promoters. This is straightforward in primates and mice and has been done in humans for other purposes, in a more localized way, such as the eyes.
Switching Neurons On
The virus is only a vector, a carrier for genetic cargo, and it is not the active virus that makes people sick. With the channel in place, a cap, wool or baseball, could cast a nonspecific cone of long-wavelength light through the skull, or a beam of ultrasound, and only the neurons carrying the tag would respond. Intensity and flicker could move those neurons from inactive to active to hyperactive, and back down.
Dialing and Safeguards
AI would most likely do the dialing rather than a knob. Someone with severe motivational problems could have the circuit stimulated more, and someone with healthy motivation could ramp it up during hard work and shut it off afterward, which gives energy output more of a square wave. Safeguards could include an AND gate, such as a pill required alongside the virus and the ultrasound. People with vagal stimulators can already unplug them.
Why use a virus to deliver genes?
Viruses evolved to get genetic material into cells, so scientists strip out the disease-causing genes and load in a payload instead. Adeno-associated virus is popular because it is small, causes no known human disease, and mostly stays outside the cell's own chromosomes. It also keeps working for a long time in cells that no longer divide, such as neurons. Different strains of it favor different cell types, which helps target the cargo.
How could ultrasound switch on cells?
The field is called sonogenetics. Some ion channels open in response to physical force, and ultrasound waves exert tiny mechanical pressure on a cell's membrane. In 2015, a team led by Stuart Ibsen at the Salk Institute made nematode neurons respond to ultrasound by giving them a mechanosensitive channel. Ultrasound can also be focused on a small spot deep in tissue.
Why can't blue light reach deep brain tissue?
Skin, bone, and brain tissue scatter and absorb light, and shorter wavelengths such as blue are scattered the most. Red and near-infrared light penetrate farther, which is why researchers favor long-wavelength light for tools meant to work through the skull. Even so, the amount of light falls off steeply with depth. That is one reason many animal studies implant an optical fiber.
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