During the series, both Tuvok and Vorik get into that reproductive state where they either have to find a mate or fight someone. Now the doc suggests to Vorik that he should try and "work it off" with the aid of a holographic substitute. He tries this and it doesn't work. However when Tuvok is in the same situation, a holographic simulation of his wife proves adequate.
I'm a bit puzzled by this. If the pon-farr
be resolved by consorting with a hologram, that would make more sense. Re-balancing the brain chemistry has to involve more than just the basic physical act, otherwise you wouldn't even need a hologram - five minutes of fun in private would do the trick. In Vorik's case it's suggested that some kind of a mind-link with the partner is essential, and that this can be forced if the intended mate is a non-Vulcan. That explains why a hologram is useless since they don't have minds. However for Tuvok it's shown to work.
Is there any reason or is it just one of those instances of writers-didn't-pay-attention-hoping-the-audience-doesn't-either?