Your computer can hold only so much data in its memory before there’s no room left. When that happens, not only can you no longer download or update new files, programs, or apps, the ones you already have often run less efficiently.
Does the same thing happen with our brains? Can our brains run out of memory storage? You may be relieved to learn that the answer is “No.” The human brain has virtually unlimited storage capacity. That’s not because of the sheer number of brain cells (the most widely cited figure is around 86 billion neurons, though that is just an estimate) but because of the way those neurons are organized.
Our Brains Have Unlimited Memory
When you learn something, many brain cells are activated at the same time. You’re not relying on a single neuron to store that memory, but on a group of neurons, and this network of neurons is activated when you recall that memory.
Each memory involves a specific network of neurons, but the same neurons can be involved in many different memories, explains Matthew Lattal, a neuroscientist at Oregon Health & Science University who studies how memories are formed.
“The brain has basically unlimited memory capacity because of the way the network can be organized,” he says.
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How Memory Works in the Brain
The cells that make up the network aren’t necessarily in the same part of the brain. They are distributed throughout the brain. Where those neurons are located depends on what kind of memory it is.
Say you have a memory of smelling a blue flower; the blue part of the memory might involve neurons in one part of the brain, while the smell of the flower involves neurons in a different part.
Still, wherever they’re located, it’s not the individual neurons, but the pattern of the network, that makes the memories different.
“It's not like there’s, say, 1,000 neurons in the brain and 10 of them are the memory of your mom and 10 of them are the memory of your dog,” says Lattal.
The potential patterns, the options for combining those 86 billion or so neurons in different ways to encode different memories, is virtually unlimited. So go ahead and memorize all the verb forms in Zulu and have a go at learning to play Rachmaninoff’s Piano Concerto No. 3. Your brain will have plenty of memory for the task. And plenty left over.
Are Our Memories Always Factual?
Brains and computers are somewhat alike in one way, however. Whenever you open a file on your computer and then close it, it re-saves the document. If you make any changes to that document, those changes become a part of the document, unless, of course, you tell the computer not to save the changes. Memories work in a similar fashion.
“Whenever we retrieve our memories, we kind of open them up so that they can incorporate new information,” says Lattal. “And they become vulnerable that way.”
This could explain why you and your siblings have somewhat (or sometimes radically) different memories of childhood. You have different memories of the same event, says Lattal, because those memories “have just naturally migrated in different directions, and it’s not clear who is right.”
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How Memories Can Change
A classic experiment demonstrated this feature of memory. When the space shuttle Challenger exploded in January of 1986, the televised event was viewed by millions of people, either live or in news coverage immediately after. It was what Lattal calls “a very salient cultural event.”
Emory University professor Ulric Neisser, known as the father of cognitive psychology, saw an opportunity for an experiment. The day after the explosion, he gave his freshman students a questionnaire asking them for details about their experiences surrounding the event, questions such as: Where were you? Who were you with? What were you doing? What time did it happen?
Three years later, he asked the same students the same questions. More than 40 percent of the respondents gave answers the second time that were inconsistent with the answers they gave the first time.
“They were completely inaccurate, yet highly confident of this memory,” says Lattal.
Similar inconsistent memories have been demonstrated in the case of other events, such as the assassination of President Kennedy or the 2001 terrorist attacks.
What’s happening in these situations, explains Lattal, is that you’ve opened up this network of neurons, and if it’s a highly salient memory, it can change in small ways each time you do that. Over many years, it can morph into a slightly different memory.
“The core of it is often there, but the details around the periphery get muddled,” he says. After a while, you’re no longer remembering an event, but remembering a memory.
So, although you don’t have to worry about running out of room to store memories, it may be difficult to 100 percent trust them.
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