why can you feel when you are close to remembering something?

There are plenty of models for how memory works at both a psychological and a physiological level. What I want to talk about now is a curious thing that happens with what is typically referred to as long-term memory. Long-term memory refers to the stuff that we remember for more than a few minutes - things like our phone number, the names of our friends, and where we live. These memories must be stored chemically in the brain. I think the current working model is that memories are somehow encoded in the strength and pattern of synapses, which are junctions between the neurons in our brains.

The curious thing about memory that I'd like to discuss now is (as you probably have inferred from the title) why can you feel when you are close to remembering something? In case you aren't with me, let me give an example. Let's say you're watching a movie; you see an actor that you've seen in many movies before, and your friend next to you says, "who's that actor?". If you know the actor extremely well, the name will flow off your tongue like a reflex. If you don't know the actor's name instantly, you will almost immediately get a feeling inside, like a gut instinct, that you can use to estimate if you'll probably come up with the actor's name if you think harder about it.

It's odd right? Somehow we can feel if further searching of our brain is likely to reveal that actor's name. And the feeling is relatively accurate. For example, I don't watch that many movies, but like many people I remember faces pretty well. So it's pretty common I'll recognize an actor's face in a movie, but I'll know that I have no idea what their name is. However, if I had previously learned the actor's name and the name was still at least weakly burned into my memory, I would get a sorta gut feeling for how likely I'd be able to dig that name out of my brain.


Ok, let's say we had a good feeling that we'd be able to find the actor's name if we think harder. What happens next?

We would start to search our brains around the areas of our brains where the actor is. Somehow we go to the memories we have for the actor, and we dig around and look through them. We'll see what other movies we can remember the actor in and what other actors we've seen him with. We can often even think of friends we know who would be able to help us answer the question. And then to move towards the actor's name, we might toss around names in our heads that feel right, so that we can listen to them and see if they sound right too. It is all a sorta fuzzy process that seems to move by intuition, but the intuition has a definite sense of direction. We can feel when we've made progress towards the name in our head even if we still do not know the name yet (e.g. we say, "I've almost got it, just give me a second"). When we do find the right name, it's like BAMM - after all that searching you've found the name, said it to yourself, and you get a sorta feeling of satisfaction that instantly lets you know that - yes that is the right name.

Why does this happen?

How does this work?

the brain isn't multithreaded

It is impossible to have more than one thought at a time.

Try it.

Try to use your brain to have two unrelated thoughts at the same time. For example think about your kids and listen to a song on the radio - being careful to listen closely and understand all of the words. You can either listen to the words or think about your kids. You may be able to swap back and forth really fast to create the illusion that you are doing both. The two may even get mixed up so that you think about how the words you're listening to relate to your kids. But if you really pay close attention, you'll notice you are either listening to the words or thinking about the kids and never doing both at exactly the same time.

I've asked lots of my friends to try the same thing - none could have two simultaneous thoughts.

So in some ways our minds must function a little like a single-processor computer (up until about 2005 almost all personal computers only had one processing core). Single-processor computers that are sufficiently fast create the illusion of multiple simultaneous computation. Although you can play your itunes and type an email at the same time, the computer is actually going back and forth between the two so fast that you don't notice it. The computer does this swapping by using memory and different buffers. It puts all the information for your email and for your itunes in a short-term memory, and then it simply goes back and forth between the two and computes the next things that need to be computing. Similarly I imagine our brains are just sticking the things we are currently multitasking into a short-term memory, and it just swaps them in and out to think about them. This process creates the illusion of thinking about multiple things simultaneously.

Our inability to have simultaneous thoughts does not preclude us from simultaneously doing multiple things. We must use the spinal cord or other neuronal cells throughout our body as the buffers to keep us running smoothly. So we can think about our next tennis shot while our arm is busy hitting the current one.