Hey so this is something that I believe is fairly recent (wikipedia page was recently updated to reflect this) and I apologize if this has already been posted.
I had read reports indicating that Levetiracetam's mode of action involved slowing the rate of activity over the corpus callosum. However, recently, UCB Pharma (they made levetiracetam, piraceta, and many others) found out the following:
UCB Pharma CNS scientists have identified the binding site for Keppra (levetiracetam) in the brain as a synaptic vesicle protein called SV2A. This protein appears to play a substantial role in the release of neurotransmitters that are essential for normal neuronal activity in the brain and spinal cord.
I thought this was worth mentioning. This is a novel mechanism of action that will most likely be a hot target for future anti-epileptic drugs.