雅思阅读 84: How the Brain Turns Action into Habit（大脑如何将行动变成习惯）

改编自 MIT Department of Brain and Cognitive Sciences / PNAS（2024年）。雅思阅读 Section 3 难度，约 1050 词。 素材来源：https://www.pnas.org/doi/pdf/10.1073/pnas.2423068122

Reading Passage

A. Every morning, before you are fully awake, you swing your legs over the bed, find your slippers, and pad to the kitchen to start the kettle. You did not plan the sequence. You did not weigh alternatives or remind yourself why each step was worth doing. The action simply unfolded, carried by something that feels less like a decision and more like gravity. Cognitive neuroscientists call this a habit, and over the past three decades their research has overturned an older assumption: that habits are simply repeated choices that have become lazy. Instead, habits are a distinct form of memory, stored in a different part of the brain, governed by different rules and triggered by different cues. Understanding how a deliberate action migrates into automatic behaviour is not merely a curiosity about daily routines; it bears directly on addiction, obsessive-compulsive disorder, rehabilitation after stroke, and the stubborn difficulty people have changing even the habits they say they hate. The everyday experience of trying, and failing, to stop scrolling a phone at bedtime is, in this sense, the same problem as an alcoholic's relapse: a behaviour stored in a part of the brain that reasoned argument does not easily reach. The gap between knowing a habit is bad and being unable to stop it is not, researchers insist, a moral failing. It is a description of how memory works.

B. The central character in this story is the basal ganglia, a small cluster of structures deep beneath the cerebral cortex that we share with fish and reptiles. Within it, the striatum acts as a sort of switchboard. Two regions of the striatum play complementary roles. The dorsomedial striatum, closer to the centre of the brain, supports goal-directed action: the kind of behaviour in which you remember that pressing this lever brought you sugar yesterday, and you care whether it still will today. It is sensitive to the value of outcomes. By contrast, the dorsolateral striatum, on the outer flank, supports habit. Once a sequence has been rehearsed enough times, control shifts from the medial to the lateral region, and the action continues even when the reward is no longer worth having. An animal trained to run a maze for food will keep running the same path long after the food has been replaced by something it dislikes; the medial system would have noticed and updated, but the lateral system simply plays back the tape.

C. A famous series of experiments by Ann Graybiel at MIT revealed what this looks like at the level of individual nerve cells. She recorded the activity of neurons in the striatum while rats ran a maze. Early in training, cells fired throughout the run, as if the animal was actively thinking about every turn. After many repetitions, the pattern changed: a burst of activity appeared at the start of the sequence, another burst at the end, and a long quiet stretch in between. The middle had been "chunked" — the entire run compressed into a single behavioural unit that the basal ganglia could execute without consulting the cortex. Later work confirmed the implication: if the cortex is temporarily silenced after a habit has been learned, the animal still performs the routine flawlessly. During learning, however, silencing the cortex abolishes it. Learning needs the cortex; automatic performance does not.

D. Dopamine is the chemical glue that consolidates these chunks. When an action is followed by an unexpected reward, dopamine neurons fire in a brief burst, and the burst marks the synapses along the path that was just used for strengthening. Over many repetitions, the cue itself — the time of day, the location, the sound of a notification — becomes sufficient to trigger the run, even when the reward is delayed or absent. This is efficient in a species that must save energy for thinking. Running a well-learned routine on autopilot costs a fraction of the metabolic effort of deliberating about each step, and the prefrontal cortex, the expensive executive organ behind the forehead, is freed for genuinely new problems. The same efficiency, however, is why bad habits are so hard to break. Once a sequence lives in the lateral striatum, reasoned arguments made in the prefrontal cortex have surprisingly little purchase on it; arguing with a habit is like asking a keyboard not to type.

E. The practical consequences have accumulated slowly. Early self-help folklore claimed that a habit formed in twenty-one days; larger longitudinal studies of real people suggest the median is closer to two months, with wide variation — some behaviours stabilise in a few weeks, others never fully become automatic. More important than the number is the architecture that the research implies. You do not abolish a habit by willing it away; you design a different cue, or insert a competing response, or raise the cost of the trigger until the old pathway weakens from disuse. Clinicians working with addiction have built treatment programmes around exactly this principle, treating craving not as a failure of will but as a well-learned sequence that must be unlearned, one repetition at a time. The basal ganglia, for its part, does not care whether the routine is healthy or harmful. It only remembers what you have done, and assumes you will do it again. The quiet lesson of the research is that the most reliable way to become the kind of person you want to be is to make the desired action so unremarkable that, eventually, you no longer have to choose it. Conversely, the surest way to break a habit is rarely to confront it in the moment; it is to redesign the day around it, so that the trigger never arrives. Willpower, the neuroscientists have concluded, is not a muscle you strengthen by forcing yourself; it is a set of environmental arrangements that you build in advance, on the days when you are still in your rational mind, for the version of yourself that will not be.

Questions 1-4

Choose the correct heading for paragraphs B, C, D and E from the list of headings below.

List of Headings i. The brain regions that switch from deliberate to automatic control ii. Why humans need the basal ganglia to survive iii. How individual neurons encode a learned routine iv. The role of dopamine in consolidating chunks v. Practical implications for changing behaviour vi. The evolutionary history of reptile brains vii. Why the prefrontal cortex is larger than the striatum

1. Paragraph B: ____
2. Paragraph C: ____
3. Paragraph D: ____
4. Paragraph E: ____

Questions 5-8

Choose the correct letter, A, B, C or D.

5. According to the passage, what distinguishes a habit from a goal-directed action? A. Habits involve the prefrontal cortex exclusively. B. Habits persist even when the reward is no longer valuable. C. Habits are always harmful to the individual. D. Habits form only in humans, not in other animals.

6. What did Graybiel's recordings show about striatal activity during maze running? A. Neurons fired uniformly throughout the run at all stages. B. Early in training, activity was concentrated at the start and end only. C. After learning, middle-of-sequence activity became a quiet "chunk". D. Silencing the cortex always prevented the run.

7. Why is chunking considered efficient? A. It reduces metabolic cost and frees the prefrontal cortex. B. It prevents dopamine neurons from firing. C. It stores habits in the hippocampus. D. It makes new problems easier to solve immediately.

8. What does the writer say about changing a habit? A. Strong willpower alone is usually sufficient. B. Twenty-one days of conscious effort is always required. C. Altering the cue or replacing the response works better than reasoning. D. Habits cannot be changed once stored in the cortex.

Questions 9-13

Do the following statements agree with the claims of the writer?

Write:

• TRUE if the statement agrees with the information
• FALSE if the statement contradicts the information
• NOT GIVEN if there is no information on this

9. The dorsomedial striatum is sensitive to whether the outcome of an action is still valuable.
10. Once a habit has been learned, silencing the cortex has no effect on performing it.
11. Dopamine neurons stop firing entirely when an action becomes automatic.
12. The early self-help claim that a habit forms in twenty-one days has been confirmed by large studies.
13. Ann Graybiel conducted her research exclusively on human volunteers.

Questions 14-15

Complete the summary below using NO MORE THAN TWO WORDS from the passage.

During learning, the (14) __________ is essential; after a habit is consolidated, the sequence is stored as a single (15) __________ in the striatum.

答案与解析

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