Has anyone seen my brain?

I don’t dwell on the missteps of my past, but I do have two very big regrets.

I’m sorry that I didn’t buy that cute little $1 million two-bedroom cottage around the block when my neighbor couldn’t give it away for $300,000. And I’m so incredibly sorry that I didn’t invest in 3M, maker of Post-its, because if I knew back then that I’d have to rely on those colorful sticky papers to remember things instead of my middle-aged brain, I would be a multimillionaire.

A forgetful one, true, but still …

My mind has begun to fail me in the most unusual ways. It often takes me a half a day to remember what I ordered for dinner at D’Angelos just two days ago, but I can remember every word to Don McLean’s “American Pie.”

What exactly is that about?

Lately, I’ve been feeling a lot like Marina, the heroine of “The Madonnas of Leningrad,” whose mind is slowly losing a battle with Alzheimer’s, but she can recall every detail of the paintings in Leningrad’s famous Hermitage museum and where they hung.

I am trying to negotiate the art of dating with a midlife brain. If you’re in a monogamous relationship, it’s no problem. But if you’re trying to play the field as I am, it can often be about as surreal as a Dali painting.

Sean and I were having a playful, leisurely morning after a playful, if slightly more energetic night. It seemed a good time to have “a talk.” Nothing serious, mind you — just a clarification of a conversation we’d had a week or so before that I’d been mulling over. Something about the “women you just sleep with” and the “women you date.”

It’s important to know which category one’s in.

“Babe, remember a few days ago we were talking about …” I started, keeping it casual, nonaccusatory and inclusive. Hey, I’ve been around men long enough to know how to kill a dialog before it even starts.

I watched as his face transformed from playful to serious and back to playful. “No, I don’t because I never said that,” he said, as he ran his hand lightly down my back and then gently smacked my butt. “Must have been one of your other guys.”

Ouch! Even though we both date others and aren’t in a committed, monogamous relationship, being confronted with an in-your-face promiscuous reality still stings.

But even worse than the ouch factor — he might have been right! One of the “other guys” might have indeed said that. No matter how careful I try to be about remembering who grew up in Philly and who in Long Beach, who has three siblings and who has two, whose ex is on Prozac and whose sister is on Zoloft, I make mistakes. Often.

The midlife brain is ripe for creating misunderstanding and utter befuddlement. It forgets things. It confuses things. It loses things.

And if you don’t have a long-standing supportive, loving network — like a husband or a committed partner — you are all alone.

I remember when my mother got her midlife brain. Objects, places and people became replaced by one word: Thing.

“Honey, can you bring the thing to me?”

“Mom, what thing?”

“You know, the thing, the thing.”

Because repeating “thing” will somehow make it clearer ...

But that was back in the days when kids were polite to their elders.

Now that I’ve morphed into a version of my mother and “thing” is increasingly slipping into my vocabulary, Trent, my 14-year-old, isn’t quite as understanding.

“Trent, honey, can you please bring the thing to me?”

“Get the friggin’ ‘thing’ yourself. I’m not your slave. I don’t even know what the heck you’re talking about. Can’t you speak English?”

So much for my long-standing supportive, loving network.

When I threw myself into the online dating world after my divorce and put my profile up on a few sites at one time, I knew I couldn’t rely on my brain alone to keep Mr. Larkspur separate from Mr. Novato and Mr. San Francisco.

At first, I printed out each man’s complete profile and carried around the three or four with whom I’d be in contact that day.

That worked OK for a while — although it practically filled a briefcase — until I got an unexpected call on my lunch hour one day.

“Hey, Kat. How are you?

“Um, good. How are you, um …?”

“Bobby. Great. You know, I really liked chatting with you. I think we should get together and take that bike ride this weekend. You game?”

My mind raced as I tried to figure out, who was Bobby? The 45-year old never-married techie from Corte Madera who looked kinda cute, or the 51-year-old-still-bitter-over-his-divorce musician from Fairfax? I hadn’t brought his dossier with me to work!

That’s when I knew I needed to carry a little bit about each guy with me at all times. So, just like in grade school, I created little crib sheets with a few basic but essential facts. Name, age, single/divorced, kids/no kids, activities, cute/not so cute. I bundled them up, alphabetized, in a rubber band and plopped them in my purse … until I switched from the heavy black leather winter purse to the creamy woven summer purse and the bundle was left at home.

Clearly, I needed help.

I needed technology.

I needed Excel. Yeah, I know it’s a spreadsheet program for businesses but I had some business, too. The business of love.

So I drove to Best Buy to check out the latest gadgets that would help me. After more than an hour of comparing the pros and cons of the BlackBerry versus the Palm versus the Treo, I left with the new Amy Winehouse CD and a frazzled brain — the very reason I needed a stupid PDA!

And then I thought, this is crazy. I’m not going to spend $400 to keep my mind and my men in order. Either my brain was going to have to get with the program, or my men were going to have to get with my brain and repeat themselves. Maybe they’d see my absentmindedness as a bit endearing.

Or perhaps I needed to date much older guys who were struggling with memory issues of their own.

When I got home, exhausted, my cell phone rang.

It was Sean.

“Hey. You know, you were right.”

“I was? See! Um, about what?”

“About women and dating and sex. I remember something like that.”

“You do?” I said, feeling a tad smug.

“Yeah.”

“And …?”

“Date.”

I had no idea what he was talking about but it seemed like the right answer. So I wrote “Date!!!” in big letters on a hot pink Post-it and stuck it on that thing that’s in my bedroom.

Gee, I wonder where he’s taking me …