Brain Leeches!

The story of the brain leech began with a chat a roleplay called Epic Heroes. An evil scientist, by the name of Dr. Tom-Bone, was being discussed with the other leader of the roleplay, ~SooEpic. The discussion of Tom-Bone's malicious weapons of destruction were the currently interest, and at one point, medical leeches got into the conversation. The concept of spider leeches came to mind, but was suddenly replaced by the brain leech. Once a torture device meant to kill a patient neurally, I took the concept into my own wing and improved upon it several months later.

The neurobiotechnological leech (Hirudo cerebralis) is usually shortened to brain leech, and is mostly robotic, 80% of it's abilities given by embedded technology. A directly cloned subspecies of H. medicinalis, brain leeches are used for the neurological treatment of a patient. Measuring in at about an inch in length and one-quarter of an inch in circumference, H. cerebralis can fit in some of the smallest areas, and in some cases, its offspring can be directly injected into the bloodstream to work internally on the human brain. As with all leeches, this leech is also born a hermaphrodite, but produces offspring once a year with an average of 1-3 leeches. After giving birth, the leech dies to feed its offspring.
The natural diet of the brain leech is blood. Rats and other sterile mammals are given to feed these creatures, and on a full stomach, they can last for about seven days before needing to feed. With the embedded technology on the leech (scientists implant the technology on birth via hypodermic needle), researchers can override the basic need for food and create coded instructions for the leech to follow. However, with this in mind, the leech's survival rate is close to zero due to the starvation of the leech. With more recent experiments, scientists have attempted to improve the nutritional value of the blood they feed to the leeches to improve their outlook, with only moderate success.
The main objective of the brain leech is to inject chemicals into the brain neurally using a hypodermic needle with the width less than the size of a hair. This is to prevent the damage of the brain, yet slip in the needle in easily and inject whatever chemical it was given (through being fed; it has a separate stomach solely for the purpose of holding compounds and solutions). The most common chemicals given are sedatives (though not commonly resorted to), dopamine, pheromones, and other human hormones to stabilize or assist in the activation of certain parts of the brain, the arousal of specific human emotion, and more recently, the ability to override the frontal cortex (more specifically the prefontal cortex) and to release coded commands to the individual, causing mind control to a degree. A normal craving sensation increased fifty times, most people succumb to the leech's implanted 'thoughts' and act upon it. Disciplined people such as monks can resist the brain leech's hold over them and even potentially killing it with their own thoughts.