This is the 2007 version. Click here for the 2017 chapter 06 table of contents.

How are Memories Stored?

We have seen that formation of one type of memory-episodic memory-involves a specific part of the brain: the hippocampus. However, other areas of the brain are involved in other forms of memory. "Memory is modular," says neuroscientist Patricia Goldman-Rakic (Service, 1993). For example, Wilson, Scalaidhe, and Goldman-Rakic (1993) found that one set of neurons was active when monkeys remembered the identity of a stimulus; another was active when the monkeys remembered the location of a stimulus. These findings converge with other data suggesting two distinct visual circuits in the brain, one for object recognition, another for object localization (see the discussion of blindsight in chapter 4). In this case memory is involved rather than perception.

What is "quite possibly" true of memory storage in the brain?

Probably each part or module of the brain remembers its own role in each distinct type of brain activity. If so, each part of the brain involved in an experience should show activity during memory of that experience later. Dingledine (1995) notes that "long-lasting changes in synaptic strength are not limited to the hippocampus but are encountered in nearly every layered structure one examines from the cerebellum to olfactory and neocortices, in keeping with the expectation that memory storage areas are distributed throughout the brain."

Brennan, Kaba, and Keverne (1990) showed that a rat's memory for sexual attractant odor was stored at the first synapse after the odor receptor. In other words, the memory was stored in the same neurons that responded to the odor. Again, memory is in the structures that participate in representing the event in the first place.

What "old principle" may apply to memory storage?

If memory is a construction, then it makes sense that memories would be stored in the same neurons that originally constructed an experience, because they are the neurons that might be called upon later to help remember it. This is like the old principle of efficient workplace organization: store at the point of first use. In other words, store something at the location where you expect to need it later. In the case of memory representation, the unique brain region involved in the experience would be the first place to look for storage of that memory. The big exception, as earlier noted, is event memory of humans, because the whole person (so to speak) participates in each episode of life. Such memories apparently require processing in the region of the hippocampus, drawing information from widespread parts of the brain and knitting it together.


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