I just pointed my browser at Dictionary.com and looked up the word "engram" with the following result (among others):
en·gram n. A physical alteration thought to occur in living neural tissue in response to stimuli, posited as an explanation for memory. Also called neurogram.
(Please note the phrase "thought to occur" and the word "posited".)
Then, just out of curiousity, I clicked on their helpful link: Get the Most Popular Sites for "engram". In the search results for that I found:
Great Engram deals! Your price, your way - that's eBay.
Um … thanks, eBay, but maybe not today…