Security Enforcer Timeout Question

If I understand correctly the security enforcer (in PHP) sets the session.gc_maxlifetime to some value. I know the default time can be set in the php,ini file. Unfortunately, on shared hosting plans you don’t have access to change that.

My question is what sort of things refresh that session? Is it just when you load a new page or refresh the current page? Or is there other interactions that keep the session alive? Perhaps there is some code you can add to change that timer?

I tried googling the subject but came up with no real helpful info.