What happens to the contact's USER record(s) when a contact is merged?

[NA]

Hi, I am trying to understand what happens to the contact's USER record(s) when a contact is merged? 

For example,  if the loser contact record has a USER record associated with it, is the USER record now assigned to the winner record?

And in that vein, If both the winner contact and the loser contact have USER records - how is that handled?

Thanks