Sensorimotor Integration

7 Long-Term Memory

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Learning Objectives

After reading this chapter, you should be able to:

• Understand the process of long-term memory consolidation.

• Describe how long-term potentiation occurs.

• Explain why multisensory teaching improves memory consolidation.

• Appraise the role of interference in long-term memory formation and explain the theories of primacy effect and recency effect.

• Discuss how rote memorization is important to long-term memory formation.

• Evaluate strategies that can help increase long-term memory in learning contexts.

• Explain why concept memory and transfer are important to success beyond the classroom.

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Section 7.2 Key Concepts About Long-Term Memory

Imagine yourself walking through a wooded area the morning after a heavy snowstorm. Even though a number of trails exist beneath the snow, you are essentially forging a new trail as you proceed where no one has yet walked through the snow. If you need to make this same journey several times during the day, you find that it takes you less time to cross the woods each time you do so. The path through the snow that you are creating becomes deeper, firmer, and faster each time you use it. Simply by using your own path repeatedly, it has become a more efficient and more durable transportation facilitator.

Construction of long-term memory is essentially the same process as the development of that efficient pathway through the snow. Just as repeated use carves out a more efficient trail, repeated activation of a new memory circuit results in the neuroplastic process that makes it more efficient, faster, and more durable.

7.1 Rewind—Fast Forward As you learned in Chapter 6, the brain constantly changes through neuroplasticity, with the development of synapses, dendrites, and myelin layering of axons in response to activation. Increased activation of a particular neural circuit strengthens that neural circuit through the neuroplasticity process. Our long-term memory storage is promoted in much the same way. This chapter will take your understanding of neuroplasticity and guide you to strategies that construct durable, long-term memories.

7.2 Key Concepts About Long-Term Memory Long-term memories are formed when information encoded in short-term memory in the hippocampus reaches the prefrontal cortex (PFC) and undergoes further activation. In the PFC, if these memories are activated and used in a variety of meaningful ways, neuroplasticity strengthens and increases their connections as they are retained in long-term memory. This is the process of using our working memory (described in Chapter 5) to work on informa- tion and then consolidate it into long-term memory. Recall from Baddeley and Hitch’s (1974) model that the central executive part of working memory roughly corresponds to neural net- works in the prefrontal cortex (Nee et al., 2013).

The prefrontal cortex appears to be related to helping us orient to, attend to, construct memo- ries about, and work on relevant information in our environment and regulate our conscious emotional states. However, for that information to be stored over the long term, synaptic changes in other brain areas also need to occur. In Chapter 6 you were introduced to the process of long-term sensitization (LTS). Recall that LTS involves the strengthening of neural connections after the neurons have become sensitized to a stimulus. For example, if an ani- mal is continually shocked, the shock leads to an increased response from the neurons and a change in synaptic connections. This type of learning is associated with the storage of implicit long-term memories.

An implicit memory is a memory for how to do something and represents one of two major divisions of long-term memory. Implicit memories are considered unconscious and are

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Section 7.2 Key Concepts About Long-Term Memory

sometimes referred to as nondeclarative memories. An example might be your memory of how to ride a bike or drive a car. These are tasks that you can perform without having to con- sciously recall the steps. Instead, you just know how to do them. In contrast, we also have an explicit memory system. Explicit memories are conscious memories for facts, knowledge, and personal experiences or declarative knowledge. Explicit memories are consolidated in the process of long-term potentiation (LTP).

Like LTS, LTP involves the increased firing of neural connections. However, LTP uses a different chemical process and, in connection with the consolidation of explicit memories, occurs in the hippocampus (Kandel, Schwartz, & Jessell, 2000). Additionally, LTP is likely to last longer and cause permanent changes in behavior. An important aspect of LTP is that the increased fir- ing of the neurons and the strengthening of the neural connections can occur without continued brain stimu- lation. For example, as you read this text your brain is creating new neural connections to store the material. When you stop reading the material, your brain will continue to strengthen those connections even in the absence of the material.

Further distinction between implicit and explicit memories can be seen by looking at amne- sic patients. Because these two long-term memory storage systems have different methods of consolidation, injury to different parts of the brain will differentially disrupt them. In Chapter 5, you were introduced to the famous case of H. M. Recall that H. M. had his hippo- campus partially removed in a surgery to alleviate epilepsy. Subsequently, he lost the abil- ity to create new memories for places, names, people, and experiences. Based on what you have learned from this text, you should recognize that this represents a loss of the explicit memory system. The problem for H. M. stemmed from the fact that his hippocampus was damaged; thus he could not engage in the consolidation of new explicit memories. How- ever, most of his previous long-term memories were still intact. He retained his childhood memories and still had a bright, normal IQ; however, he did lose some memories he formed in the years before the surgery (Kandel, Schwartz, & Jessell, 2000). This would suggest that although synaptic changes occurring in the hippocampus result in the consolidation of long- term memory, the hippocampus is not the ultimate storage place for long-term memories. Instead, long-term memories are stored throughout the brain in areas of the sensory cortex and the prefrontal cortex.

H. M.’s case also provides information on the working of the implicit memory system. After the surgery, H. M. was able to learn new motor tasks at a normal rate. This was illustrated in an experiment whereby he was taught to trace the outline of a star while watching his hand in a mirror (see Figure 7.1). At first this task is difficult, but as participants practice it, their per- formance becomes better. Although H. M. had no recollection of completing the activity, his performance improved over time, indicating that he was learning (Blakemore, 1977). Kandel, Schwartz, and Jessell (2000) report that tasks that tend to be reflexive and not reflective, require no conscious awareness or complex evaluation, and only require the individual to respond to a cue are generally spared in individuals with damage to the hippocampus. Thus, the implicit memory system includes memory for reflexive behaviors, skills or habits, and associative learning, which means it activates many brain areas as well. For example, a fear response to a snake might be acquired through activation of the amygdala when one has a

Ask Yourself Make a list of five activities you’ve committed to implicit memory. (Tip: your answer to the “Ask Yourself ” on neuroplastic construction in Chapter 6 might be of help.)

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Section 7.2 Key Concepts About Long-Term Memory

fearful experience with the snake. In associative learning, where we learn to respond to a cue, changes in motor and sensory systems occur. For example, if you eat something that makes you vomit, you are likely to feel nauseated the next time that you see the food. In this case, the sensory systems associate the taste, smell, and sight of the food with the feeling of being sick. As a result, you learn to avoid the food.

Figure 7.1: H. M.’s drawing task

By the third day of trials, H. M. could draw the star from his reflection with ease, even though he had no explicit memory of doing so.

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Section 7.3 Multisensory Experiences

As you can see, long-term memories, then, require the increased strengthening of neural connections throughout the brain. Long-lasting changes in our knowledge are most likely to occur when the prefrontal cortex helps us pick out information in the environment, work on it, connect it with prior knowledge, and strengthen neural connections in the hippocampus through the process of LTP.