Read the passage. Then answer the questions.

Question

from "Why We Remember . . . and Forget"

by Faith Hickman Brynie

1 Have you ever studied like mad for a big history test, only to forget everything you knew on test day?

2 Have you ever gone to the store for three items and returned with only two? Do you remember every detail of your seventh birthday party but can't recall who your teacher was that year? If you answered "yes" to any of these questions, chances are you have a perfectly normal brain that's working exactly the way it should!

3 Scientists have learned more about the brain in the last decade than in all the years before that combined. One big reason is the development of new technologies such as PET and fMRI that let researchers capture images of the action inside the living brain. By looking at the areas where fuel and oxygen are being used in the greatest amounts, they can tell which parts of the brain are doing what job.

What is Memory?

4 There are several different kinds of memory, and the brain handles each differently. Primary or short-term memory works for about 15 to 20 seconds. That's long enough to keep a telephone number in mind and dial it. Secondary or working memory lasts longer. You use it when you converse with a friend or work through several steps in a math problem. It lasts as long as you need it, then disappears. Long-term memory works over a lifetime. It stores knowledge of objects and language, important events, facts, procedures (how to do things), and motor skills such as riding a bicycle.

5 Different areas of the brain specialize in the kinds of memories they store—a specialization we usually aren't aware of until something goes wrong. For example, doctors in Japan are treating a patient who suffered damage to the front part of the brain's temporal lobe (at the side of the head). The man can remember common nouns, such as the names of fruits, vegetables, and animals, but he cannot recall proper names such as famous people, friends, or relatives. He has lost not only the memory of all the proper names that he knew, but also his ability to learn new ones.

6 Memory depends on a process called long-term potentiation, or LTP. "Potentiate" means to promote or strengthen. LTP strengthens the pathway that nerve impulses follow as they move from one neuron (nerve cell) to another. The pathway is related to the structure of the cells. A neuron is made up of a cell body, plus strands or fibers that extend outward from it. A single axon carries impulses away from the cell body. Dendrites—often many of them—carry signals toward it. A traveling signal passes from the axon of one neuron to a dendrite on the next, but axons and dendrites do not touch.

7 How does the signal jump the gap? When a nerve impulse reaches the end of an axon, it triggers the release of a chemical called a neurotransmitter. Neurotransmitter molecules diffuse across the space and attach to outer surfaces of dendrites, starting a signal there.

8 For LTP to work, a chemical messenger must travel from the receiving cell back to the transmitting cell, reinforcing the bond between them. One such messenger is the gas nitric oxide. It is so unstable that it lasts only a few seconds, but that’s long enough to bolster the pathway.

9 Memory may also depend on the development of new neurons. The hippocampus is a part of the brain essential to memory formation and storage. Scientists at Yale and Rutgers have found that the number of new neurons in one region of the hippocampus doubles when adult rats learn certain kinds of new skills. Investigators at the Salk Institute in California have found that the activity of running on wheels has a similar effect on mice.

10 Neurons in the hippocampus encode the information used to perform short-term memory tasks. When rats learn to press levers, for example, different parts of the hippocampus go to work at different times, depending on which lever is to be pressed and how long the animals have waited since "learning" which lever will earn them a reward.

When Memory Fails

11 Once a memory forms, it's far from permanent and accurate. "Imagine you were at a scene of a crime," says New York University scientist Karim Nader. "Someone asks you if you remember a person with a red jacket. In reality, there was no one with a red jacket there. When you call up the memory of the crime scene, it becomes labile [open to change], creating an opportunity for suggested or created images of a person with a red jacket to be stored with the original memory." The instability of memory is chemical, Nader thinks. Proteins are made when a memory is stored. Every time it is retrieved, new proteins must be made in order to store it again. That means memories can change each time they are recalled.

12 If remembering is potentiation, then forgetting is depotentiation. Depotentiation weakens the pathway between neurons. Low-frequency stimulation has that effect, but certain neurotransmitters prevent it. When learning is rewarded, for instance, neurons release the neurotransmitter dopamine. Dopamine doesn't necessarily strengthen the connection. It just stops it from eroding.

13 Body chemistry, age, and emotion influence depotentiation. Chemistry may explain that experience of forgetting everything you ever knew on exam day. Scientists have found that rats with high levels of stress hormones in their blood forget how to run mazes. Human beings given the stress hormone cortisol have trouble remembering facts. The retrieval of spatial memories seems especially susceptible to the action of stress hormones—hence that mental blank for the hard-working student who is nervous about a history test.

From "Why We Remember…and Forget" by Faith Hickman Brynie, from Odyssey Magazine, March 2001. Copyright © by Carus Publishing d/b/a Cricket Media.
Question
How does dopamine affect depotentiation?
Responses

Dopamine helps prevent the connections between neurons from wearing down.
Dopamine helps prevent the connections between neurons from wearing down.

Dopamine strengthens the pathway between neurons.
Dopamine strengthens the pathway between neurons.

When more dopamine enters the brain, memories are more reliable.
When more dopamine enters the brain, memories are more reliable.

When depotentiation occurs, dopamine helps to reverse the damage.
When depotentiation occurs, dopamine helps to reverse the damage.

Answer 1

The correct response to how dopamine affects depotentiation is:

Dopamine helps prevent the connections between neurons from wearing down.

This can be inferred from the passage, specifically in section 12, where it mentions that "dopamine doesn't necessarily strengthen the connection. It just stops it from eroding."