I believe my hippocampus was damaged at some point within the past ten years. Most people who know me say I have bad memory, but I found out today I don’t. I only have bad episodic memory. My semantic memory is just fine, perhaps even exceptionally good. According to some scientists referenced on Wikipedia, the hippocampus is a section of the brain that handles episodic memory, and does not handle semantic memory.

My hippocampus also handles my sense direction. I don’re remember having better episodic memory ten years ago, but I do remember having a better sense of direction. And I also don’t remember my bad memory being a defining trait ten years ago, so I’m assuming it was okay at some point and then it went bad. Damage to my hippocampus would explain this.

Episodic memory is the kind of memory your friends notice you not having. You forget that time you went on that trip together, or what they told you yesterday, or some other episode that defines your friendship. You’re still a nice guy, just kind of insensitive. This is me. Except I’m not insensitive (I swear!); these things just don’t stick in my brain.

I think semantic memory, on the other hand, is commonly misunderstood as intelligence. People who know me tend to think I’m “smart,” but I really just have good semantic memory. I pick up programming concepts or games quickly because they are inherently semantic. Every part has a defined meaning. But I don’t remember the episode of learning the concepts. They just become part of my mental model of the world, my semantic memory.

So assuming I’m correct that my hippocampus was damaged, what might have caused that? Other scientists referenced on Wikipedia say it might have something to do with autism and/or maybe Alzheimer’s. You’ll recall I once diagnosed myself as having Asperger’s, a mild form of autism. And Alzheimer’s increasingly seems to be a kind of diabeties in the brain, interesting here because I am diabetic.

For a less scientific-sounding explanation, there was that one time I jumped into a doorway and hit my head so hard I had to be taken to the emergency room. I don’t actual remember that episode, but the story of that episode is essentially the meaning of the scar on my forehead. (See the distinction there?) That happened within the timeframe I suspect my hippocampus was damaged. But the location of the hippocampus (near the center of the brain) makes that seem less plausible.

Or maybe my hippocampus wasn’t damaged at all. Maybe I always had bad episodic memory and just don’t remember it when I was younger. That would, of course, make sense. In any case, it’s nice to have an explanation for why I remember some things and not others. I can now stop telling people I have bad memory only to have them later discover I remember some things very well. Now I can say, more correctly I think, that I have semantic memory.