Strobila

The Strobila (ストロビラ) is a device, developed by Academy City researchers, which is intended to manipulate a person's mind without interfering with their brain by altering the balance of hormones secreted by the heart.

Etymology
The Strobila is named after in a  life cycle.

Appearance
The main body of the Strobila is made of plastic and is only a few millimetres long. Extending from it is a single fiber, more than 20cm long and thinner than a hair, which runs all the way to the subject's heart.

Principles
The Strobila is a product of research into carrying out highly accurate mental control without interfering with the brain, which is closely linked to esper development. The human mind does not solely consist of the brain - aside from the chemicals released there, the other organs secrete various hormones which influence a person. In the Strobila's case, it stimulates the heart in order to alter the balance of secreted hormones, manipulating the mind without even touching the brain.

Research papers related to the strobili suggest using the method as a new restraint for out-of-control espers or efficiently controlling offenders at juvenile hall, though they were probably tacked on afterwards given that researchers generally give no thought to compromises with society except with regards to funding.

Mental Out Arc
At some point in November, a Strobila was secretly installed in Shokuhou Misaki's neck, as part of Mitsuari Ayu's attempt to take revenge on her. After noticing differences between the appearance of the Ground Geo power station and how she remembered it, Shokuhou suspected that someone may had tampered with her memories. This led her to visit Kumokawa Seria, one person capable of doing such a thing. Suspecting that some sort of machine might be responsible, Seria examined her body, finding the Strobila imbedded in the back of her neck and removing it.

After losing contact with the Strobila in Shokuhou Misaki's neck, Mitsuari had Yamakawa and several other people posing as Emergency Aid workers attempted to replace it under the guise of treatment for instability. Shokuhou saw through their deception and thwarted their attempt, learning in the process that the Strobila actually had no data in it, leading her to realize that it was a decoy meant to fool her into manipulating her own memories.

Later, when she was attacked at Ground Geo, Shokuhou found a Strobila embedded in her assailant's neck and ripped it out, suspecting that it was allowing her opponent to resist her Mental Out. The Strobila wasn't actually responsible, but Mitsuari acted as though it was to fool Shokuhou and catch her with a surprise attack.