Longman Dictionary of Contemporary English
The Collaborative International Dictionary
Pre- \Pre-\ [L. prae, adv. & prep., before, akin to pro, and to E. for, prep.: cf. F. pr['e]-. See Pro-, and cf. Prior.] A prefix denoting priority (of time, place, or rank); as, precede, to go before; precursor, a forerunner; prefix, to fix or place before; pre["e]minent eminent before or above others. Pre- is sometimes used intensively, as in prepotent, very potent. [Written also pr[ae]-.]
Douglas Harper's Etymology Dictionary
word-forming element meaning "before," from Old French pre- and Medieval Latin pre-, both from Latin prae (adverb and preposition) "before in time or place," from PIE *peri- (cognates: Oscan prai, Umbrian pre, Sanskrit pare "thereupon," Greek parai "at," Gaulish are- "at, before," Lithuanian pre "at," Old Church Slavonic pri "at," Gothic faura, Old English fore "before"), extended form of root *per- (1) "beyond" (see per).\n
\nThe Latin word was active in forming verbs. Also see prae-. Sometimes in Middle English muddled with words in pro- or per-.
Wiktionary
pre. 1 Before; used to form words meaning "in front of (in space)". 2 Before; used to form words meaning "before (in time)".
Usage examples of "pre-".
Bullock, S, Rose, S P R, and Zamani, R Characterisation and regional localisation of pre- and postsynaptic glycoproteins of the chick forebrain showing changed fucose incorporation following passive avoidance training.
Patterson, T A, Gilbert, D B, and Rose, S P R Pre- and posttraining lesions of the intermediate medial hyperstriatum ventrale and passive avoidance learning in the chick.
If habituation occurs by reduction of the postsynaptic response at a single synapse, it could logically be a consequence of either pre- or postsynaptic processes, or of course a combination of both.
This question of pre- versus postsynaptic plasticity has been a major source of polemic in recent years, but with most theoreticians favouring the postsynaptic side as the main site of plasticity.
This effect, essentially an increase in the efficacy of transmission between pre- and postsynaptic cells, was termed potentiation.
LTP, thus moving the focus of interest about mechanism from the pre- to the postsynaptic side.
As a result the models for the mechanism of LTP had to be revised to include an effect mediated through the phosphorylation of specific pre- and postsynaptic membrane proteins.
Although the debate over whether the pre- or the postsynaptic changes are the most important is still raging as I write, it is likely to turn out, as is sometimes but not always the case in science, that both camps are more or less right.
All that I know so far - at least, all that is worth telling here - is that there are a number of different glycoproteins of a variety of molecular weights, on both pre- and postsynaptic sides of the membrane, involved in the response to training on the bead.
Ott, J and Matthies, H-J Some effects of RNA precursors on development and maintenance of long-term memory: hippocampal and cortical pre- and posttraining application of RNA precursors.