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Memory and the brain

How Memory Works

Help Linked Module: The Memory Exhibition at the Exploratorium Linked Module: The Prefrontal Cortex Linked Module: Phineas Gage - A Man Who Hurt His Brain
Chercheur  :  Patricia S. Goldman-Rakic, Neuroscientist, Dies at 66

In the course of a day, there are many times when you need to keep some piece of information in your head for just a few seconds. Maybe it is a number that you are “carrying over” to do a subtraction, or a persuasive argument that you are going to make as soon as the other person finishes talking. Either way, you are using your short-term memory.

In fact, those are two very good examples of why you usually hold information in your short-term memory: to accomplish something that you have planned to do. Perhaps the most extreme example of short-term memory is a chess master who can explore several possible solutions mentally before choosing the one that will lead to checkmate.

This ability to hold on to a piece of information temporarily in order to complete a task is specifically human. It causes certain regions of the brain to become very active, in particular the pre-frontal lobe.


This region, at the very front of the brain, is highly developed in humans. It is the reason that we have such high, upright foreheads, compared with the receding foreheads of our cousins the apes. Hence it is no surprise that the part of the brain that seems most active during one of the most human of activities is located precisely in this prefrontal region that is well developed only in human beings.

Human memory is a complex phenomenon, however, and of course involves other regions of the brain as well.


Linked Module: Why Is It Called the Hippocampus?

Though the hippocampus is an essential brain structure for the proper functioning of long-term memory, it cannot be regarded as the “memory centre” in the same sense that the occipital cortex, for example, can be regarded as the centre for processing visual information.

The reason is that long-term memory is not located in just one specific area of the brain. The hippocampus is the catalyst for long-term memory, but the actual memory traces are encoded at various places in the cortex.

The destruction of both hippocampi (as the result of a stroke, for example) has disastrous effects on long-term memory, preventing the individual from learning anything new whatsoever. The most important evidence of the role of the hippocampus in transferring long-term memories has been provided by subjects who had sustained damage to both hippocampi and could not keep things in their memories for more than a few moments.

Experiment Module: Spatial Learning in Rats with a Damaged Hippocampus

Information is transferred from short-term memory (also known as working memory) to long-term memory through the hippocampus, so named because its shape resembles the curved tail of a seahorse (hippokampos in Greek). The hippocampus is a very old part of the cortex, evolutionarily, and is located in the inner fold of the temporal lobe.

All of the pieces of information decoded in the various sensory areas of the cortex converge in the hippocampus, which then sends them back where they came from. The hippocampus is a bit like a sorting centre where these new sensations are compared with previously recorded ones. The hippocampus also creates associations among an object’s various properties.

When we remember new facts by repeating them or by employing various mnemonic devices, we are actually passing them through the hippocampus several times. The hippocampus keeps strengthening the associations among these new elements until, after a while, it no longer needs to do so. The cortex will have learned to associate these various properties itself to reconstruct what we call a memory.

Source: Collection of Carol Donner

But the hippocampus and the cortex are not the only structures involved in long-term memory and its various manifestations in the brain.

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