Would it be possible to produce a pair of human brains that are connected by a wormhole that has each end inside one of the brains? What I had in mind is that the wormhole would have neurons inside it so that nerve signals could travel through the wormhole to keep the brains connected. Each brain would be in a different universe so the wormhole inside the two brains would connect two different universes. Also would it be possible for one of the brains that is connected through the wormhole to be poisoned and for the other to be unpoisoned or would poisoning one of the brains poison the other brain?
One possibility is that the brains have implanted hardware that controls the brain to machine to wormhole interface.
The way I understand the science, a wormhole would be a sub-atomic, quantum type thing. Not something that you could put anything real through. A signal of exotic energy on the other hand could possibly work.
As to how two brains in separate universes got linked, a version of the multiverse theory, where the same person in two parallel universes had the same idea, created similar hardware and turned it on at the same time...
As to the poisoning part, no fluids would be able to go through, so no poison can cross, unless it's thought based like snow crash.
Sixth dimensional quantum entanglement is the way to go.
Quantum entanglement is a physical phenomenon that occurs when pairs or groups of particles are generated or interact in ways such that the quantum state of each particle cannot be described independently — instead, a quantum state may be given for the system as a whole.
So if you entangle two particles, put them in seperate human brains, somehow link them up to said brain and allow them to send information to one another by stimulating neurons you got a pretty much undetectable way to communicate between said brains. Having this work on brains in different dimensions... I'm not sure if it works, given that science has yet to pull this off (I think).
As for the poison? Make it some kind of overload on the entangled part of the brain and give the person a seizure, or send a constant annoying buzzing sound, make the person smell rotten bananas 24/7 or trick the brain into making an excess of something that's dangerous to have inside of your body in large amounts or stop making certain things that you need in order to live.
Sync brain activity across the wormhole using light or radio.
Neurons communicate via chemical signalling. Getting this to work across a wormhole could be tricky. One possibility is optogenetics -- controlling brain activity with light (via genetic modification of neurons to express light-sensitive ion channels). This would allow you to use a wormhole which might only be able to handle the transmission of simple photons, as opposed to the more complex organic chemicals that neurotransmitters are composed of. Similarly, some sort of brain-computer interface might allow EM spectrum transmissions across the wormhole bridge; some methods such as fMRI are non-invasive. Both of these technologies are in active development, a bonus for realism.
As far as poisoning goes, it would depend on what was used. Something chemical in nature which simply caused cell death or the imbalance of neurotransmitters in one brain -- through the overdose of an SSRI, for example -- would not affect its twin, as you were only using the wormhole bridge to transmit the changes in existing chemical potentials, and you could not transmit the introduction of a physical substance. However, if the poison merely tricked the first brain into triggering a harmfully large dump of an extant quantity of neurotransmitters, then this action could be "mirrored" to the neurally linked twin. Likewise, the syncing transmission of the "death throes" of a poisoned brain could very possibly cause damage to its twin (unless, perhaps, there were countermeasures in place to cut off the receiver in the event of anomalous brain activity from the sender).