Memory
Similarly, the basic neural mechanisms of memory are increasingly being worked out. When you have
an interesting experience such as attending a concert, your neurons fire in patterns that together
capture your experience of the concert. Forming a memory of the concert requires changes in your
neural connections that will enable you to retrieve a memory of the concert in the future. To
understand memory, we need neural theories of both storage and retrieval.
Storing memories in the brain is not like saving a computer file, which can immediately produce a
record that can be fully re-created in its original form. The perceptions that form your experience of
the concert are first captured by neural populations in your hippocampus, a brain area so crucial that
people with damage to it sometimes become incapable of forming any new memories at all. But
permanent storage of your concert memory requires interactions between the hippocampus and
regions of the cortex, the outer layer of the brain. Storage in both areas is another case of learning, as
described in the next section, produced by changes in the synaptic connections between neurons.
Retrieval of a memory works by reactivating a pattern of firing in a population of neurons. Suppose
someone starts telling you about another concert that is similar to the one you went to, perhaps
because the bands played the same kind of music. Hearing about the new concert may produce a
pattern of firing in roughly the same populations of neurons that encoded the various aspects of the old
concert. The newly generated pattern of firing will then generate additional neural activity by virtue
of synaptic connections, possibly producing a pattern of firing that is roughly similar to your original
experience. That activation of a firing pattern of neurons constitutes your recalling the memory.
Many different kinds of experiments support the hypothesis that memory is a brain process. I have
already mentioned the sad case of people with damage to the hippocampus who are unable to form
memories. When people with Alzheimer's disease lose their memories, autopsies show buildup of
plaques that have destroyed neural connections. Brain scans measuring the flow of blood to regions
as small as a few millimeters show what anatomical areas become active when people are presented
with stimuli of different kinds similar to ones they remember. Together, such experiments provide
strong evidence that when you remember something, it is because your brain has revived patterns of
neural activation.