As mkh9 pointed out, the solvents used in magic markers are universally neurotoxic, with the exception of some markers especially produced for children (and even then the safety claims are suspect). Thus, sucking on a marker will produce brain damage, the amount of which depends upon the frequency of exposure and the length of exposure.
It depends on what kind of markers and what chemical is in them. It is possible.
Do you know what type of marker and what kind of chemical is in the marker? You can google that and find out. Some chemicals can cause brain damage like huffing glue. It could change personality also. It depends on the chemical used. Usually alot of them are non toxic though. It may say on the marker. You can call a poison center they know more.