Since it is not so easy to imagine and visualize the behaviour of the muscles in the fingers, hand, and arm of a violinist performing a fast and accentuated trill vs. a slow and soft vibrato, I try to imagine and visualize how corresponding motor neurons do fire.
I assume there are some motor neurons that are immediately responsible for the speed and amplitude of the movement of a finger performing a fast trill, and — partly the same, partly others — that are immediately responsible for the speed and amplitude of the movement of the same finger performing a slow vibrato.
The behaviour of these motor neurons — during the trill or the vibrato — can be recorded as corresponding sequences/trains/bursts/chats of spikes.
How may these spiking and/or bursting patterns look like?
Maybe like this?