So, my main character has to fight a group of old friends with have all gone, extremely rogue. They are wreaking havoc like never seen before, and they need to be stopped. He wants to stop them, but not to kill them. The military has gone gen him some equipment, most importantly, needles The when injected, will cause a person to go into a seizure so powerful, that they will be put into a permanent comatose state. Bryan doesn’t want to kill his friends, and he has a PhD in....whatever science is required to do this. So he creates something that will cause an extremely localized and concentrated seizure in one part of the body. My question is, is it possible to do that?
Seizures can Cause Permanant Damage
I work in corrections, and for some reason a suprising number of criminals a seem to suffer from siezures, I see about one or two a month. I've seen guys have grand mal siezures so bad that they fracture thier skulls on the floor. They usually wet themselves, lose memory, and sometimes even never recover them. Even a small seizure is a very serious health issue. The problem is that siezures dont occur in a specific body part, but deep in the brain itself. Anything which is causing seizures is going to effect the entire brain and also the rest of thier body.
The next problem is that administering drugs to perform a specific effect requires a specific and detailed health information like bodyweigh, body fat percentage, and possibly other factors as well. Even then, when you are messing with body chemistry it really is a shot in the dark, they usually start you off on psychotropic drugs on a dosage based on scientifically educated guess, see how you respond personally since everyone is different, then adjust accordingly. Not exactly conducive to non-lethal darts. Maybe the same dose in one guy is enough to kill him while in another it just gives him a bad headache.
Better Methods Exist Already
Tasers are mean. They are really really mean. Not stun guns, but actual tasers, which fall under the umbrella of the incredibly clinical yet incredibly sinister sounding family of weaponry known as Electronic Control Modules (or ECMs). The way ECM's work is by hijacking the brains ability to send messeges to the muscles. So as long as positive contact is made all muscle groups effected not only cannot recieve messeges from the brain, but they are now recieving instructions to contract as hard as possible. Whats really neat is that the heart operated on a totally different frequency so it is not effected (though everything else is.) As long as the electrical pulses are being recieved the muscles will contract. Ive been tazed in my line of work several times, its like paralysis. You cannot move, you cannot scream, you can't even wet yourself. All you can do is maybe whimper a bit and clench your entire body, which seems to be vibrating in tune with the evil cackle of electricity thrumming in waves through your body. Its kind of like the worst charlie horse/muscle cramp youve ever had, but over your whole body. Plus being set on fire. Then rolled through broken glass.
This is why the police carry ECM's which only pulse for 5 seconds. We refer to it as the time machine because its the longest 5 seconds of your life. The civilian models can range anywhere from 10 seconds to 60 seconds. After 60 seconds of this the recipient will be unconscious, as you cannot breath when being tazed. So Why not zap them for 4 to 5 minutes, long enough to cause permenant brain damage due to oxygen deprivation.
But, before I finish I feel I must point out a flaw in your charecter's logic.
Your Charecter's Morality Is Wrong
Killing is bad, but a permanant vegatative state following a violent seizure is okay? At that rate just shoot the poor bastard and be done with it. It's kind of like how batman believes killing is wrong but has no problem with sending the joker to the worlds least secure asylum so he can escape and kill again and again and again. At some point you need to face the facts and just admit these guys are too rabid to be allowed to continue wreaking havoc and put em down. A permanant coma isnt any more humane than just getting it done and over with the old fashioned way. Unless your charecter is a sociopath/narcissist who has convinced himself that his experimental remote lobotomy torture drug is being administered for his victim's own good then his logic just doesnt add up for somebody smart enough to posess a PHD.
Seizures happen when there is uncontrolled increased neurologic activity in your brain. Because the brain controls your body this leads to various effects.
Epileptic seizures basically come in two varieties: Focal seizures, where only one part of the brain is affected. Generalized seizures, where the whole brain is affected. Focal ones can convert into generalized ones.
A focal seizure of the area controlling let's say the left arm would present itself with involuntary contractions of this arm. The subject would be aware and conscious during this.
A generalized seizure usually involves contractions all over the body, loss of continence, sometimes a very dangerous tongue bite, followed by a period of unconsciousness. Seizures can vary in length, but are usually about 5 to 10 minutes long. After that the subject will remain unconscious or extremely sleepy for some time, maybe a couple of hours.
So what you are proposing is definitely possible, there are a lot of substances that can cause or increase the risk of seizures, but I don't know how quickly they act. But I'm sure it's theoretically possible to have something that acts very quickly, reliably and has consistent results.
Source: Medical student, so take all this with a grain of salt.
If you want a body part other than the brain to be disabled you don't want to cause a seizure - seizures happen in the brain.
If ypu try to mess.with the nerves electrically, then it is akin to tazing. Again, not localized to where it hits.
There is no way to get what you want other than inducing good, old, comedy gold stinging pain. You may be interested in the Starr sting scale. That scale rates the most painful insect bites, with the bullet ant sting at the higher end of the spectrum.
That sting also features high on other pain scales. From the ant's own wiki:
The pain caused by this insect's sting is reported to be greater than that of any other hymenopteran, and is ranked as the most painful according to the Schmidt sting pain index, given a "4+" rating, above the tarantula hawk wasp, and according to some victims, equal to being shot, hence the name of the insect. It is described as causing "waves of burning, throbbing, all-consuming pain that continues unabated for up to 24 hours".
What you want is a mini device that emulates the insect's loving kiss, both mechanically and chemically. Preferably something that can be shot from a tranquilizer gun, or a mini drone thay can fly up to your client and do its magic on his di...gits.
That will give you the effect you were looking for.
Bonus if you activate it to the sound of Tom Lehrer's song The Masochism Tango.
A seizure results from the miss-firing of motor neurons.
Yes it is possible to incapacitate someone by forcing their motor-neurons to miss-fire. The problem you'll run into, especially with a delivery-mechanism as crude as an injection, will be with localization.
Your cells are semi-permeable...stuff can get through them. Stuff that's small enough to interface with synapses of motor-neurons would absolutely diffuse into the rest of the body from the point of injection. I'm fairly certain you could do this now with concentrated sodium or potassium...although getting those elements in a state where they would be bio-active in a non-"melt your arm off" kind of way, would be tough. Doable, but tough.
I'd just use a taser.
What I'd be looking for instead of chemical injection would be a novel spin on the good ol' fashioned electron-pump we call a taser. Tasers induce current by the release of electric potential. This is exactly what your motor-neurons do, except the driving force isn't a self-contained sodium/potassium pump, it's lithium ions & a copper circuit.
Believe it or not, I've actually held some hypothetical conversations with other physicists about hijacking a person's motor-cortex via an electromagnetic field...we're no where near this. You could totally kill a person this way, but we lack both the understanding of our central cortexes, and we also have an acute lack of volunteers.
With a better understanding of the human nervous system & an extremely precise EMF generator producing several simultaneous fields, you could theoretically induce tempered seizures at some point where the fields are in superposition with one another. It would work the same way triangulation does, except instead of call/response, you'd be microwaving brains.
Light and sound and smells. The best way to induce severe seizures in a very healthy person without using tasers or poisons, is to induce a maximum overload of their brains. As I said in another answer, these guys' skin is nearly indestructible, but they still must rely on sensorial inputs', or they'd be deaf and blind.
First step: sound. A strong soundwave on several frequences to keep the listener confused and in pain.
Second step: light. A wash of stroboscopyc light that must grow even more intense as they close their eyes.
Third step: smells. No toxic substances, just a concentrations of what's vile and nauseating to a vomit-inducing level.
At this point, the brain is trying to process too much information, the body can't react to everything. the rogues fall on their knees trembling, in pain, alive but temporary vulnerable to be subjugated with the coma mdrug
It sounds like what you're looking for is localized loss of brain function, explainable by a common medical issue. As others have mentioned, a seizure may not be what you're looking for, as they can occur without causing long-term damage. But, in people not prone to seizures, the most common cause of a seizure is a stroke, which does cause long-term damage. A stroke is just localized cut-off of blood flow to a part of the brain. Going with that, let's cause some brain damage and cause a seizure!
Given your resource of needles, and a surgical training, your protagonist could inject ... pretty much anything sticky (glob of fat to be discrete, or a plastic if not necessary), in the arteries feeding the primary motor cortex. Alternatively, an advanced sonic/laser device could be used to lesion the same arteries. The enemy would then observe the world naturally, be able to move their eyes, and have normal breathing and heart rate, but not be able to voluntarily move their body.*
If a seizure is needed (eg: for a cover story), tramadol or something similar could be injected as well. This drug has a strong tendency to cause seizures, and a relatively short half-life, so that an emergency room may not detect it, and thus assume the seizure was caused by the stroke.
*(eventually they could relearn some crude movements, but nothing dangerous ... maybe typing at an abysmally slow rate).