Long-Term Memory

Importance of Long-Term Memory

The importance of long-term memory to thought cannot be overemphasized. One of the earliest examples of its significance is still one of the best. In the 1930s, Sir Frederic Bartlett had people listen to folktales from foreign countries and later asked them to recount the stories. Not surprisingly, he found that these unfamiliar stories were not remembers very accurately. What was surprising was that the errors of recall were not random but were quite systematic. The subjects often rewrote the stories in their own minds, espcially parts that were particularly foreign to them, revising the plot to the point where it resembled a more familiar Western narrative.

To explain his findings, Bartlett proposed that “Remembering is... an imaginative reconstruction, or construction, built out of the relation of our attitude towards a whole active mass of past experiences.” He concluded that when we face a problem, we draw upon mental schemata, organized bundles of stored knowledge. For example, if you are asked a question about how baseball is played, you would draw upon a baseball schema, your collective knowledge of baseball obtained from specific direct experiences you've heard or read about baseball. Barlett's findings do not just concern the personal, idiosyncratic, and fallible nature of memory, but also emphasize how long-term memories, when retrieved into the temporary workspace of working memory, can guide our thoughts and actions, as well.

It has been known for centuries that we can only keep a few things active in our minds (in working memory) at once. George Miller, one of the pioneers in cognitive psychology, figured out, through psychological experiments, that the magic number is about seven pieces of information. Some people can hang on to eight or nine, whereas others manage only five, but, on average, temporary storage can hold about seven times. (It's probably no coincidence that telephone numbers within an area code were designed to have seven digits). But, as Miller noted, we can effectively expand that capacity by chunking or grouping information – it's about as easy to remember seven letters as seven words or ideas. No doubt one of the reasons human cognition is so powerful is because we have language in our brains, which exponentially increases the ability to categorize information, to chunk. A whole culture, for instance, can be implied by a name.

Damage to the frontal lobe interferes with the ability to plan and execute goal-directed behavior. Frontal lobes are involved in executive functions (planning, problem-solving, and behavioral control), as well as in short-term or temporary memory. Illustration by Elena.

The concept of working memory subsumes what used to be called short-term memory. But as the term workspace implies, working memory is more than just an area for temporary storage. It underlies mental work. As Minsky noted, thinking involves juggling of mental items – comparing, contrasting, judging, predicting. It is the job of the executive functions of working memory to do the juggling.

In the spirit of viewing the mind in terms of computer-like operations, some cognitive scientists like Time Shallice and Phillip Johnson-Laird have referred to executive functions as supervisory or operating system functions. A computer operation system is responsible for controlling the flow of information processing, moving information from permanent memory (ROM) to a central processing unit with active memory (RAM), scheduling tasks to performed using the active memory, and so on. Similarly, executive functions are involved in the constant updating of temporary memory, selecting which specialized systems to work with (pay attention to) at the moment, and then moving relevant information into the workspace from long term storage by retrieving specific memories or activating schemata pertinent to the immediate situation. Through executive functions, specialized systems are also directed to attend to certain specific stimuli and to ignore others, depending on what working memory is working on. In complex tasks involving multiple kinds of mental activities, executive functions plan the sequence of mental steps and schedule the participation of the different activities, switching the focus of attention between activities as needed.” Executive functions are crucially involved in decision-making, allowing you to choose between different courses of action given what is happening in the present, what you know about such situations, and what you can expect to happen if you do different things in this particular situation. Executive functions, in short, make practical thinking and reasoning possible.

The executive represents a powerful mental capacity, but is not all-powerful. Like the workspace, it has its limits. It basically can do one or at most a few things at a time, this is why you forget a phone number if you are distracted while dialing. With practice and training, we can learn to divide our attention between two mental tasks simultaneously, but only with difficulty. In this sense, the executive is more like an old-fashioned DOS operation system that can only run one program at a time than like a multitasking Windows operation system that can concurrently run word processing, spreadsheet, e-mail, calendar and other programs.

But there's also a sort of chunking that takes place in executive functions. As we've seen, the executive is involved in scheduling the sequence of steps in a complex task. Here, the executive is doing more than one thing at a time, but the things are all related to the overall goal. If the executive has to work on multiple unrelated goals at the same time, however, the system begins to fall apart, especially if the goals conflict with one another. An easy way to stress people is to make them do too much at once. Planning, decision-making, and other aspects of mental life suffer when the executive is overloaded. Working memory has come to be thought of as a function of neural circuits in the frontal lobes. 

(From Synaptic Self. How Our Brains Become Who We Are. Joseph LeDoux (author of The Emotional Brain).

Neural activity, as measured with devices such as PET and MRI scans, increases in the frontal cortex when humans perform tasks that require temporary storage and executive functions. Photograph by Elena.