The Middle Voice.

I need a lesson on the middle voice.

I've read that Hittite only had the active and mediopassive voices,
but that residual PIE, at its breakup, had active, middle and passive
voices.

It's difficult to explain the middle voice in English.

I remember being taught in Greek class about the Greek middle voice,
with the rubric 'for it/myself'. I remember thinking 'I brushed my
teeth' would probably be a Greek middle. It seems to require a verb
that can describe an action done by the grammatical subject to itself;
something like Jocasta, just before expiring, exclaiming "I
kill+[middle-ending]" would seem possible for 'I suicide'.

What's the difference between the middle and mediopassive voice? Is
there a better way to explain it?

As I understand it, a middle voice verb looks to its agent, explaining
the action done by the agent, in a sense that is absolutely lacking in
English, that is, the agent (or grammatical subject) is not so much
doing the action, as having the action done to it by the verb.

This question arises from an article in the current JIES that
addresses old PIE as an ergative language. This is "Lithuanian and
Indo-European Parallels" by William R. Schmalstieg. I'll eventually
get to this article in a later posting: I need to re-read the thing
several times over. It presents some reconstructed PIE sentences in
the 'active present' and 'middle preterit'. Reading between the lines,
I think Schmalsteig is saying old PIE (ergative stage) managed what we
today do in the active and passive voices by moving some statements
into the middle voice, or maybe, the mediopassive, with the whole
thing being wrapped up in the concept of 'transitivity'.

Aggh! Ergativity!