Is it possible to do physical damage to another human using a CrMe or PeMe spell? Other RPGs often include some sort of psionic striker with a mental blast that does damage. I see a few spells that reduce a person's ability to act, like Weight of a Thousand Hells, but nothing that causes damage or could lead to death directly.
Why would you want to do that with mentem? It's so very unsubtle - plenty of other Arts that allow direct damage effects.
also: It is (AFAIC) out of paradigm - it's very much a sci-fi "psionic" effect, it doesn't have that medieval feel (to me anyway, YSMV).
You could turn the target's mind solid using a MuMe spell akin to Inmost Companion, but with a Rego requisite added to make the solidified mind appear inside the target's body - that would probably cause some damage.... 
Not directly. I'd steer away from direct comparisons with other game systems as they tend to have different needs (i.e. ensuring that a psionic can still dish out damage during those all-important combat encounters).
As you've already identified, Mentem in Ars Magica is principally about control. You might not be able to project a mental blast, but you can tell a man to stab his friend or throw himself from the tower, potentially. By which time you're hopefully some distance from the unfortunate results. It's dangerous, but in more subtle ways.
To be honest, I'd see that sort of thing as PeCo, plausibly with range Sight or Arcane.
Whyever would you want to do physical damage with it?
You can reduce someone to a mindless husk. You can remove all their memories. You can drive them insane.
All far, far more intimidating than mere physical damage.
I figured as much. My question was in part posed because I'm still fairly new to Ars and I wanted to know if it could be done. Why would I want to do damage with Me and not another form? Cause I have a good score in Me, of course. Easier to learn spells, better penetration, etc. I agree it doesn't fit with Ars. I'll look into more indirect attacks. Thanks.
First - heh, you said "psionic". 
Okay - as above, no, no direct damage with Mentem. Just doesn't work that way in AM.
However, there are plenty of ways to achieve "brain death" of one stripe or another in the PeMe guidelines. Even short of Base 15, your mage could go Base 10 and, say, remove the ability "to make a decision". That would pretty much take someone out of action. See HoH:Societatus, Jerbiton chapter for more ideas on Mentem and "mental abilities" to target.
example:
You can make the target believe that she is a fish. She will then kill herself.
You can make the target call the Pope a liar.
You can make the target do a million other suicidal things.
So all you need is a bit of creativity to use mentem to kill.
The GMs i´ve played with allows causing temporary mental damage with PeMe, at a very low rate of effect(ie making it rather hard to just do "random generalised damage" to someones mind, much easier to just make them think they´re really a big bird and say doesnt that cliff look like just the perfect place to fly off from...).
For simplicity usually just running it as normal wounds, except with no physical wounds.
Works reasonably well enough.
Really? That´s news to me. I could have sworn the idea originated from the bad old tales of the nasty sorcerers that made people go "aaargh, i think my head just exploded" just by attacking minds with their foul magic.
Which would be PeCo, neh?
Psionic attacks in other game systems seem to me to be more like "using mental powers to physically hurt someone" . Which just sounds like using magic to do harm. Which in ArM is PeCo.
Even if it is the brain which explodes doesn't make it a Mentem attack, that's mostly just flavour. If any major organ explodes then it sucks to be you.
Mmm, if someone THINKS their head just exploded, i would say that it FELT like it, as otherwise they wouldn´t have much to think with any longer?
Temporarily making someone THINK they hurt like hell, PeMe, not PeCo, but the effect should be similar.
Or maybe Creo (Perdo) Mentem, or maybe a effect ttat use guidelines Mu(In)Me(Co) to make the pain greater.
Adding in Co means you would be actually causing real pain, Me is then just a useless addition.
I agree it might be argued as CrMe though, as what you´re doing is creating something, that it happens to be damaging to the target is an indirect result unless the spell is specifically designed to cause actual damage to the mind as well.
I thnk that is the example from to work on "human" beings without one mind, but yes senses, making feel the pain: the savage boys that don't age ore the typical revenant, that aren't true intelligent but yes sensible.
On another side, i was using the guidelines or recomendations from HoH: Societates, making feel (Mentem) better their bodys (Corpus), but it is more a cosmetic i can admit.