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Memory and the brain
Forgetting and Amnesia

Help Imaging memory loss with aging (seccond article of the page) fMRI Reveals Dynamics of Working Memory Anatomie de l'hippocampe
Memory (animations)
Patricia Goldman-Rakic : Neuroscientist searching for keys to memory
Getting a Grasp on Working Memory

A large body of evidence indicates that the dorsolateral prefrontal cortex plays an important role in certain forms of memory work, in particular those that involve alternating between two memory tasks and exploring various possibilities before making a choice.

It seems fairly certain that this area of the brain holds information required for reasoning processes that are in progress. But its precise role remains the subject of much debate. Does this prefrontal area basically coordinate the activities of slave sub-systems, as in Baddeley’s model of the phonological loop and the visual/spatial sketchpad? Or does it actually itself serve as a temporary storage area for certain types of information, as Goldman-Rakic’s research tends to indicate? Might the level of abstraction of the task be the deciding factor, or might the size of the workload determine whether this area comes into play?

As all these unanswered questions suggest, the anatomical substrate of working memory is far from being understood in detail. Moreover, the phenomenon of working memory is made all the more complex by the fact that it takes place over time.

Source: NIMH Laboratory of Brain and Cognition. Published in Nature, Vol. 386, April 1997, p. 610.

  For example, the experimental results illustrated here show how various areas of the subjects’ brains alter their activity levels as the subjects are presented with various visual stimuli. When the subjects are shown a blurred image, the activity level (represented by the blue bars in the graph) becomes highest in area 1, the visual part of the brain. When the subjects are shown an image of a face, brain activity (black bars) becomes highest in the associative and frontal regions (4, 5, and 6). Lastly, when the subjects are retaining an image of a face in their working memory, brain activity (red bars) is highest in the frontal regions, while the visual areas are scarcely stimulated at all.

It has also been observed that distinct processes appear to be involved in the storage and recall of items memorized with the phonological loop and the visual/spatial sketchpad.

One thing is certain: the prefrontal cortex plays a fundamental role in working memory. It enables people to keep information available that they need for their current reasoning processes. For this purpose, the prefrontal cortex must cooperate with other parts of the cortex from which it extracts information for brief periods. For this information to eventually pass into longer-term memory, the limbic system probably has to be brought into play.



Le circuit de Papez, le syndrome de Klüver et Bucy, les trois cerveaux de MacLean
How we learn to value others
Original modules
History Module: The Quest for the “Emotional Brain” The Quest for the “Emotional Brain”

The hippocampus receives connections from the cortex’s primary sensory areas, unimodal associative areas (those that involve only one sensory modality), and multimodal associative areas, as well as from the rhinal and entorhinal cortexes. While these anterograde connections converge at the hippocampus, other, retrograde pathways emerge from it, returning to the primary cortexes, where they record in the cortical synapses the associations facilitated by the hippocampus. Thus, even in the mechanism of memorization, we find the feedback loops so often encountered at all levels in the living world.

Tool Module: Cybernetics

For a piece of information to be recorded in long-term memory, it must pass through Papez’s circuit. Injuries to this circuit can result in memory impairments.
For example, a lesion in the mammillary bodies is responsible for an amnesic syndrome whose most classic example is Korsakoff’s syndrome. In addition to the confabulation, confusion, and disorientation that accompany this syndrome, patients suffer from anterograde amnesia: they cannot store new information in their long-term memory. The most typical cause of this syndrome is vitamin B1 deficiency, often seen in chronic alcoholics.


Recent research has provided a complex, highly intricate picture of memory functions and their loci in the brain. The hippocampus, the temporal lobes, and the structures of the limbic system that are connected to them are essential for the consolidation of long-term memory.

The hippocampus facilitates associations among various parts of the cortex, for example, between a tune that you heard at a dinner party and the faces of the other guests who were at the table. However, all other things being equal, such associations would naturally fade over time, so that your mind did not become cluttered with useless memories. What might cause such associations to be strengthened and eventually etched into long-term memory very often depends on “limbic” factors, such as how interested you were in the occasion, or what emotional charge it may have had for you, or how gratifying you found its content.

The various structures of the limbic system exert their influence on the hippocampus and the temporal lobe via Papez’s circuit, also known as the hippocampal/mammillothalamic tract. This circuit is a sub-set of the numerous connections that the limbic structures have with one another. The diagram here shows the route that information travels from the hippocampus to the mammillary bodies of the hypothalamus, then on to the anterior thalamic nucleus, the cingulate cortex, and the entorhinal cortex, before finally returning to the hippocampus.

Once the temporary associations of cortical neurons generated by a particular event have made a certain number of such “passes” through Papez’s circuit, they will have undergone a physical remodelling that consolidates them. Eventually, these associations will have been strengthened so much that they will stabilize and become independent of the hippocampus. Bilateral lesions of the hippocampus will prevent new long-term memories from forming, but will not erase those that were encoded before the injury.

With this gradual disengagement of the limbic system, the memories will no longer pass through Papez’s circuit, but instead will be encoded in specific areas of the cortex: the same ones where the sensory information that created the memories was initially received (the occipital cortex for visual memories, the temporal cortex for auditory memories, etc.).


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