Cognitive Psychology: Connecting Mind, Research and Everyday Experience, 3rd Edition

Memory and the Brain • 191

One outcome of these changes at the synapse is a phenomenon called long-term

potentiation (LTP)—enhanced fi ring of neurons after repeated stimulation (Bliss &

Lomo, 1973; Bliss et al., 2003; Kandel, 2001). Long-term potentiation is illustrated by

the fi ring records in Figure 7.16. The fi rst time neuron A is stimulated, neuron B fi res

slowly (Figure 7.16a). However, after repeated stimulation (Figure 7.16b), B fi res much

more rapidly to the same stimulus (Figure 7.16c). LTP is important because it shows that

repeated stimulation causes not only structural changes but also enhanced responding.

Results such as these indicate how experiences can cause changes at the synapse.

Memories for a particular experience cause changes in many thousands of synapses,

and a particular experience is probably represented by the pattern of fi ring across this

group of neurons. This idea of memories being represented by a pattern of fi ring is simi-

lar to the idea of distributed coding we introduced in Chapter 2 (see page 40).

WHERE DOES MEMORY OCCUR IN THE BRAIN?

So far we have been focusing on synapses. But zooming out from these synapses to look

at the brain as a whole provides another way of considering the connection between

memory and the brain. One question we can ask is which areas in the brain are involved

in memory. The fi rst answer we can give to that question is that memory does not occur

in one specifi c place. Just as perception and attention are distributed across many dif-

ferent areas, so is memory.

We have already seen that the frontal cortex is important for working memory

(see Chapter 5, page 138), but that many other areas are involved as well. A similar

situation occurs for LTM, with many different areas being involved. We begin with the

medial temporal lobe (MTL), which contains the structures shown in ● Figure 7.17.

One of the most clearly established facts about memory and the brain is that the hippo-

campus, one of the structures in the MTL, is crucial for forming new LTMs. We know

this from the case of H.M., who lost his ability to form new memories (anterograde

amnesia) and also lost much of his old memory (retrograde amnesia) after his hippo-

campus was removed (see Chapter 6, page 155).

● FIGURE 7.17 (a) Side view of the brain and (b) underside of the brain, showing the

amygdala and structures in the medial temporal lobe (perirhinal cortex, parahippocampal

cortex, entorhinal cortex, and hippocampus).

Amygdala Amygdala

Hippocampus

Perirhinal

cortex

Parahippo-

campal

cortex

Entorhinal

cortex

(a) (b)

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