Here at the Curiosity Desk, we love nothing more than hearing from you about what is piquing your curiosity. A recent email to the ol' Curiosity Desk inboxreads...

“Every day when I drive, I find that there are fairly long stretches when my mind wanders but I seem to manage to stay on the road, making all the right turns. How am I doing that without crashing or going off the road? How is my brain compensating for my lack of attention?” 

Well, what better way to understand what’s happening in the brain when we get behind the wheel than to go for a ride in my trusty 2007, manual transmission Toyota Yaris – with a neuroscientist?

As Boston University Professor Howard Eichenbaum climbed into the passenger seat, he explained exactly what it is he spends his time thinking about, researching and teaching.

"Essentially, I study the brain and how it accomplishes the phenomenology of memory," he said.  

As we pulled out onto Commonwealth Avenue I quickly learned that, when you have a neuroscientist in your car, you immediately start to realize just how complex driving is. It’s kind of miraculous, actually. Here I was, talking, listening, watching the road, signaling, steering, working the clutch, shifting gears – all at the same time – as if it was nothing. Much to my dismay, Eichenbaum explained that it wasn't because I am a particularly skilled driver, but simply that I am lucky enough to have a fully-functioning human brain.   

"There are multiple systems in the brain that accomplish memory and cognition, and can do so basically independent of one another," he said.

It’s two memory systems in particular, centered in different parts of the brain, that are key to answering today’s question.

The first is called the declarative system. This is your active memory center. You use this all the time to make decisions about everything from what to have for lunch to how to get around.   

"The conscious brain system, the declarative system that we have, really has maps of the information in our head," said Eichenbaum. "All kinds of information: What’s your family tree? Who was your favorite professor in college? And among those sorts of information are geographic maps in your head."

So, if you’re driving and thinking to yourself, 'OK. I need to take a right on Beacon Street and then a left on Exeter Street', you’re using your declarative system. If you're following a GPS’ instructions, watching out for exit 29 in two miles? Declarative system. When I got semi-lost while driving around with Eichenbaum somewhere in Brookline, and was trying to figure out where I was? Declarative system.

"You try and use the parts you do know and the parts you don’t know," explained Eichenbaum. "You try to use visual cues that are on your map [in your brain] like ‘Where’s Commonwealth Avenue?’ And you infer what would be a logical route to go for, which is what you’re doing right now."

But there’s another system hard at work when we’re driving as well: The implicit or habitual memory system. This system forges its memories largely by doing. It’s why you can accelerate or brake, turn left or right, without really thinking about it. And its why, once you learn, riding a bike is just like … well … riding a bike.

"That’s this habit system," said Eichenbaum. "It’s so wonderful that way that it can just completely take over, out of consciousness, on its own."

But there’s more to it that just muscle memory. Over time, the habitual system also learns to handle a whole host of other common occurrences on the road, from simple road rules – like red lights mean stop and green light means go – to more complex rules, like changing lanes.

"It can be a really complex sequence of actions," said Eichenbaum. "And it will respond to contingencies. You look in your mirror and it's clear, but then you look back and it's not. So you pause. It's very interactive, but still completely unconscious." 

And if you drive a particular route enough – for example, your work commute – your brain also locks that path into that same habitual system. This frees up the declarative system to do all sorts of other things, even get lost in thought for long stretches, while you cruise along essentially on autopilot.  

"And so, we can talk and think, have a separate conversation going on while this other system in the background, in this implicit way, performs its function of remembering everything from driving the car to the route you’re taking without having to explicitly think about or express your memories for how to get from one place to another," said Eichenbaum. 

Eichenbaum says that – in general – the brain favors the habitual system when it’s available. He points out a real-world example that might sound familiar to you (it’s certainly happened to me).

Here’s the scene: You’re going to out to dinner. You hop in the car, and the first leg of your route to the restaurant is the same as your work commute.

And then your mind drifts off and you start thinking about 'Who am I going to meet for dinner?' or whatever. Or some other crazy thing. And suddenly you’ve passed up the exit to go to dinner and you find yourself at work (laughs).

But crucially, the declarative system still remains available. This is important when, for example, there’s a detour on your route and you have to actively figure out how best to get where you’re going. Or when, say, you notice an ambulance heading toward you and have to decide where and when to safely pull over.

Eichenbaum stresses that just because large parts of your driving experience are guided by your habitual system, it doesn’t mean you can take your eyes off the road. Distracted driving is still distracted driving. So, keep that cell phone out of reach. The texting can wait. Besides, wouldn’t you rather use that available declarative system brain power to take in all the interesting stuff on the radio?