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.

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.

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.