How can I find out what newsgroups are available ?

[Terence Mark]

   Can anyone tell me how I can find out what newsgroups are available ?
   I have a little book detailing about 40 of them, but it's quite obvious
there are many more than that.
   Specifically, I'm looking for a newsgroup dealing with physiological 
psychology and/or neuroscience; even more specifically I'm looking for one
that deals with brain stimulation and/or brain reward.
   Any help will be much appreciated.