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Memory and the brain
Sub-Topics
Forgetting and Amnesia

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Help Link :  Multitasking Behaviors : To do or not to do Link :  Working Memory Link : Memory (animations)
Researcher
Research :  Patricia Goldman-Rakic : Neuroscientist searching for keys to memory
Original modules
Tool Module: Brain Imaging Brain Imaging

SHORT-TERM MEMORY
LONG-TERM MEMORY

Baddeley’s model of working memory has proven especially fruitful for research on the brain areas involved. This model posits a central processor that coordinates the activity of two sub-systems. Many brain-imaging studies show high activity in the frontal lobe when this central processor is working.

Source: NIMH Laboratory of Brain and Cognition. Published in Nature, Vol 386, April 10, 1997, p. 610

 

For example, the image shown here was produced by functional magnetic resonance, a technique based on the increased blood flow to the most active areas of the brain. In this image, taken while the subject was holding an image of a face in his memory, the yellow area in the prefrontal cortex is very active.

 

But Baddeley’s model also postulates the existence of a phonological (acoustic and linguistic) memory and a visual/spatial memory (containing mental images). Brain imaging studies have also revealed distinct neuroanatomical bases for both of these forms of memory.

The phonological loop activates certain areas in the left hemisphere that are associated with the production of language, such as Wernicke’s area and Broca’s area. Visual/spatial memory seems to be associated with a region of the occipital cortex generally associated with visual processing.

Meanwhile, certain sub-regions of the prefrontal cortex are activated only if the memorization exercise is somewhat difficult for the subject, thus confirming the coordinating role of the central processor.

Things get even more complicated when you consider the chronological sequence of memorization: the various steps involved in storing and retrieving a piece of information.



       

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Link :  Pathways to Declarative Memory Link :  Pathways to Procedural Memory Link :  Memory and the Hippocampus Link :  Le chef d'orchestre de la mémoire spatiale
Link :  Le rôle éphémère de l'hippocampe dans la mémoire Link : Memory (animations)

Suppose you are in a museum admiring a painting. Your retinas capture the image of this painting and route it, in the form of nerve impulses, to the visual zone of your brain, which reconstructs the overall image. These impulses are then routed to your hippocampus, which acts as the gatekeeper and decides whether or not to accept the information and pass it on to your long-term memory. If your hippocampus does not let this information in, you will probably forget the image of the painting within a minute. But if your hippocampus does accept this information, it will eventually be returned to the area it came from: the visual cortex. There the image of the painting will be placed in long-term memory, point by point, in the form of thousands of strengthened connections between neurons. 

The hippocampus appears to play a fundamental role in spatial memory in many animal species, including humans. For example, in a British study, the researchers asked taxi drivers to imagine their travels through the city of London, while their brain activity was monitored by positron emission tomography (PET scan). This task, which was so familiar to these subjects, caused a specific activation of their right hippocampus. In human beings, the hippocampus may therefore contribute to the construction of episodic memory by providing a spatial framework for each memory that lets it be reconstituted accurately.

LONG-TERM MEMORY
SHORT-TERM MEMORY

The hippocampus, the cortical structures surrounding it, and the neural pathways that connect them to the cortex as a whole are all heavily involved in declarative memory–the memory of facts and events.

For example, after you’ve had a fine dinner with some friends, your memories of their faces, the taste of the wine, and the music that was playing are distributed in the various visual, olfactory, and auditory areas of the brain, but they are all connected together by the hippocampus to form an "episode", rather than remaining a collection of separate memories.

The hippocampus thus plays a fundamental role in episodic memory, the kind that will let you remember this especially pleasant dinner party years later. In fact, it seems to be the hippocampus that enables you to “play the scene back”, by reactivating this particular activity pattern in the various regions of the cortex. This phenomenon would be very important during dreams, and would explain the incorporation of events from the last few days into them.

 

But after a while, these various cortical regions activated during an event would become so strongly linked with one another that they would no longer need the hippocampus to act as their link. Thanks to this linkage, the memory of a piece of music that was playing that night could be enough to bring back the entire scene of the dinner party. Each of these elements could act as an index entry that lets you retrieve all the others to your consciousness.

 

Thus, information that has been encoded in long-term memory for a lengthy period of time no longer requires the intervention of the hippocampus. This is the case in particular for general knowledge in semantic memory, which instead activates the frontal and temporal cortexes. The activity in the temporal lobe would correspond to the activation of the fact in question, while the activity in the frontal cortex would correspond to its reaching consciousness.

 

Unlike our memory of facts and events, however, our spatial memory appears to be confined to the hippocampus. And more specifically to the right hippocampus. This structure seems to be able to create a mental map of space, thanks to certain cells called place cells.

 

 

Some very intense personal memories that bring what is sometimes called emotional memory into play appear to involve another structure of the limbic system besides the hippocampus. This structure is the amygdala, which is already known to manage our reactions to fear. Many other structures in the limbic system also help to encode our long-term memories.

Lastly, procedural memory, such as knowing how to ride a bike, does not appear to involve the hippocampus at all. Instead, procedural memory appears to be associated with modifications in the cerebellum, the basal ganglia, and the motor cortex, all of which are involved in motor control. As evidence to this effect, procedural memory is not affected by amnesia caused by lesions to the hippocampus, but is affected by damage to the cerebellum and by neurodegenerative diseases that alter the basal ganglia, such as Huntington’s disease.

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