Why I think going into convulsions is related to the radio signal
My theory is that the reason the infected go into convulsions is because anger disrupts their ability to communicate.
They stay in constant communication via sending out radio signals on the frequency that Manousos discovered. That's their telepathic, or telempathic, connection with each other.
Emotions like anger or hate that trigger a "fight or flight" type of response somehow disrupt their brains' ability to send/receive the radio signal. The virus sends a panic response to the body when it registers that the radio signal is disrupted from any individual brain. Because all of infected are connected all of them get the same panic response and go into convulsions.
I think that if you were to put an infected person into a Faraday cage, the same convulsions would happen.
Disrupting their communication for a long enough time might be the key to freeing people from the hive-mind.