Ryan, like many on the spectrum, has a fantastic memory. To clarify: he has a fantastic memory for certain types of details, like the length of each track on a CD, or the order in which we picked up groceries, or all the words to every movie he's ever seen. Ask him where he left his toys or to identify his own grandmother by name, though, and you're on your own.
This kind of memory is known as Declarative Memory, and a strong declarative memory can help compensate for some deficits that go hand in hand with autism, like learning a script of what one should say in a specific social situation.
I think the brain wiring behind the awesome memory has something to do with keeping the memories readily accessible for longer than usual, rather than overwriting and pruning the neural connections. Don't quote me, this is just my hypothesis: I'm not a brain scientist, and I'm totally making this up.
My anecdotal supporting evidence is rooted in my observations of how Ryan seems to experience time. For Ryan, something that happened months ago is just as current as something that happened five minutes ago.
Today for example, we were having a perfectly relaxed evening, playing checkers and looking up cookie recipes, when Ryan suddenly flew into a panic, bordering on a meltdown. His heart was racing, his face crumpled with anguish. He shrieked, "We will not see Hard Red any day this year!?!"
Several minutes of interrogation and calming strategies later, we figured out that he meant that he had lost a tiny plastic Angry Birds toy (the red bird) somewhere in the basement... at some point in 2015. This was the first Stu or I remembered hearing that it was missing.
In Ryan's head, last year might as well be yesterday. When this memory surfaced for Ryan, he experienced it with all the urgency we would expect to see if he had lost that toy today. (Side note: I found Hard Red within 5 minutes of learning that it had gone missing. I am just that good.) Today, last month, that one afternoon when he was seven, it's all the same to him, and it's all fresh.
His memory is a blessing and a curse.