EigoPro 1級 読解 — The Neuroscience of Addiction: When the Brain's Reward System Is Hijacked

For much of the twentieth century, addiction was framed in starkly moral terms: the addict was a person of deficient character, undone by a failure of will. Neuroscience has steadily dismantled that view. Far from being a vice to be scolded out of existence, addiction is now most usefully recast as a disorder of learning and motivation—one in which the very circuitry that evolved to guide us toward food, shelter, and companionship is quietly turned against us. Central to this reframing is a correction of a popular misconception. Dopamine, the neurotransmitter most associated with addiction, is not the molecule of pleasure it is so often called. Its principal task is to encode a prediction error: the gap between the reward an organism expects and the reward it actually receives. When an outcome exceeds expectation, dopamine surges and the preceding behaviour is reinforced; when the payoff disappoints, firing dips below baseline. Dopamine, in other words, drives anticipation and learning rather than enjoyment itself. Addictive drugs exploit this machinery directly, flooding the system with a signal far larger than any natural reward could produce, and teaching the brain, with brutal efficiency, that nothing else is worth wanting. The consequences of this hijacking are insidious, taking hold gradually and almost imperceptibly before the user fully grasps what has happened. Through neural plasticity, the pathways linking drug-associated cues—a place, a smell, a time of day—to craving are progressively strengthened, while the prefrontal regions that govern restraint and long-term judgement are correspondingly eroded. The result is a cruel asymmetry: the impulse to seek the drug intensifies just as the capacity to resist it weakens. This explains why craving can persist long after any pleasure has vanished, and why relapse so often defeats sincere resolve. To dismiss such behaviour as mere weakness of will is to misread the biology entirely. None of this absolves the individual of agency, but it does reveal how thin the line between choice and compulsion can become. Understood this way, addiction demands not condemnation but evidence-based, compassionate care—and a public conversation honest enough to follow the science where it leads.

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この単元の問題を3問、解説つきで公開しています

1級 · 読解 · 全5問

問 1

Which statement best captures the central argument of the passage?

  • Addiction is fundamentally a failure of willpower that neuroscience has largely failed to explain.
  • Addiction is better understood as a learning disorder that hijacks the brain's reward circuitry than as a simple matter of pleasure-seeking or moral weakness.
  • The dopamine system exists primarily to generate feelings of pleasure, which addictive substances amplify beyond natural limits.
  • Recovery from addiction is impossible because the neural changes it produces are wholly permanent and irreversible.
Phrase

全体の論旨

/learning disorder, hijacking the reward system/
1級読解主旨把握論旨
⚡ひとことで

依存症は意志の問題ではなく、報酬学習回路を乗っ取る学習障害として捉えるべき、というのが核心。

選択肢の解説Choice Analysis

「Addiction is better understood as a learning disorder that hijacks the brain's reward circuitry than as a simple matter of pleasure-seeking or moral weakness.」

正解

パッセージ全体は依存症を「意志の弱さ」や単なる快楽追求から切り離し、ドーパミンが快楽ではなく学習(予測・動機づけ)を担うという神経科学的知見に基づいて、報酬回路が「乗っ取られる(hijack)」過程として描いている。第2段落の incentive salience と第3段落の可塑性の議論がこの主旨を支える。したがって「学習障害として理解すべき」が最も論旨を要約している。

  • 「Addiction is fundamentally a failure of willpower that neuroscience has largely failed to explain.」

    = 依存症は意志力の欠如であり神経科学は説明できていない ━ 本文は冒頭で道徳的弱さ説を明確に退け、神経機構で説明しているため矛盾。

  • 「The dopamine system exists primarily to generate feelings of pleasure, which addictive substances then amplify far beyond their natural limits.」

    = ドーパミンは快楽を生み出す系で薬物がそれを増幅する ━ 本文はドーパミンが快楽ではなく予測・動機づけを担うと明言しており部分的に正しいが核心を取り違えている。

  • 「Recovery from addiction is impossible because the neural changes it produces are wholly permanent and irreversible.」

    = 神経変化は完全かつ恒久的で回復は不可能 ━ 本文末は可塑性ゆえに回復の余地があると示唆しており矛盾。

▦Collocation
パターン意味例
hijack the reward system報酬系を乗っ取るAddictive drugs hijack the reward system.
a learning disorder学習障害Addiction is reframed as a learning disorder.
moral failing道徳的欠陥It is no longer dismissed as a moral failing.
reward circuitry報酬回路The reward circuitry is repeatedly overstimulated.
recast X as YXをYと捉え直すScience recasts addiction as a brain disease.
❝例文

  • The author recasts addiction not as vice but as a disorder of learning.

    筆者は依存症を悪徳ではなく学習の障害として捉え直す。

  • Drugs hijack circuits that evolved to guide survival behaviour.

    薬物は生存行動を導くために進化した回路を乗っ取る。

  • The thesis hinges on dopamine's role in prediction, not pleasure.

    この論旨はドーパミンが快楽ではなく予測を担う点に懸かっている。

  • Such a reframing carries profound clinical implications.

    こうした捉え直しは重大な臨床的含意を持つ。

💡Tip · 覚えるコツ

主旨把握では、冒頭で筆者が何を「退ける(dismiss/reject)」か、何に「置き換える(recast/reframe)」かの対比構造を掴むこと。C2 では選択肢が「部分的に正しいが核心ではない」形で並ぶため、細部の事実一致より論証全体の重心を問う。

問 2

According to the passage, what is the primary function of dopamine in the brain's reward system?

  • It permanently suppresses the prefrontal cortex so that impulsive behaviour becomes automatic.
  • It generates the subjective sensation of pleasure that follows the consumption of food or drugs.
  • It is released only when an organism encounters an entirely novel and unexpected stimulus.
  • It encodes the discrepancy between expected and actual rewards, thereby driving anticipation and learning rather than producing pleasure itself.
Phrase

ドーパミンの機能

/prediction error, anticipation/
1級読解詳細ドーパミンの役割
⚡ひとことで

ドーパミンは期待と実際の報酬のずれ(予測誤差)を符号化し、快楽ではなく予期と学習を駆動する。

選択肢の解説Choice Analysis

「It encodes the discrepancy between expected and actual rewards, thereby driving anticipation and learning rather than producing pleasure itself.」

正解

第2段落はドーパミンが「快楽の分子」という通説を退け、期待と結果の差(予測誤差)を符号化して anticipation と learning を駆動すると述べる。報酬が予測を上回ると放出が高まり、行動が強化される。よって「予測と実際のずれを符号化し予期・学習を駆動」が本文の説明と一致する。

  • 「It generates the subjective sensation of pleasure that immediately follows the consumption of food, alcohol, or other drugs.」

    = 食物や薬物の後に来る快感そのものを生む ━ 本文はまさにこの通説を退けており(not the molecule of pleasure)矛盾。

  • 「It permanently suppresses the prefrontal cortex so that impulsive behaviour becomes automatic.」

    = 前頭前野を恒久的に抑え衝動を自動化する ━ 抑制は第3段落の別文脈で語られドーパミン放出の主機能ではない、すり替え。

  • 「It is released only when an organism encounters an entirely novel and unexpected stimulus.」

    = 完全に新奇で予期せぬ刺激のときだけ放出される ━ 予測誤差は新奇刺激に限らず期待との差で生じるため過度に限定的で不正確。

▦Collocation
パターン意味例
prediction error予測誤差Dopamine signals a prediction error.
encode a signal信号を符号化するNeurons encode the reward signal.
drive anticipation予期を駆動するDopamine drives anticipation of reward.
fall short of expectation期待に届かないWhen reward falls short, firing dips.
reinforce behaviour行動を強化するThe signal reinforces the preceding behaviour.
❝例文

  • A larger

    than-expected reward spikes dopamine release. — 予想以上の報酬はドーパミン放出を急増させる。

  • When the payoff disappoints, firing drops below baseline.

    報酬が期待外れだと発火は基準値を下回る。

  • This signal teaches the brain which actions to repeat.

    この信号は脳にどの行動を繰り返すべきかを教える。

  • Pleasure and wanting are dissociable in this model.

    この枠組みでは快楽と渇望は分離可能である。

💡Tip · 覚えるコツ

科学ジャーナリズムでは「通説を述べてから否定する(not X but Y)」構文が頻出。X(快楽)を正解と取り違えやすいので、否定辞と逆接(rather than / not...but)を必ず追跡し、筆者が肯定する Y を答えに据える。

問 3

What does the passage identify as a key consequence of repeated drug use for the brain's circuitry?

  • The dopamine system shuts down entirely, leaving the user unable to experience any form of motivation.
  • The brain compensates by generating new reward circuits that eventually restore normal motivation.
  • The prefrontal cortex grows more active in order to override the intensified cravings.
  • The neural pathways linking drug-associated cues to craving are strengthened while the prefrontal regions governing restraint are progressively weakened.
Phrase

反復使用の帰結

/cue-craving pathways, weakened restraint/
1級読解詳細神経可塑性の帰結
⚡ひとことで

反復使用で手がかり→渇望の経路が強化され、抑制を担う前頭前野が弱まるという非対称な変化が起きる。

選択肢の解説Choice Analysis

「The neural pathways linking drug-associated cues to craving are strengthened while the prefrontal regions governing restraint are progressively weakened.」

正解

第3段落は可塑性により薬物関連の手がかりと渇望を結ぶ経路が強化される一方、自制を司る前頭前野の制御が徐々に侵食される(eroded/weakened)と述べる。この非対称が「やめたいのにやめられない」状態を生む。よって「経路強化と前頭前野の弱化」が本文に合致する。

  • 「The brain compensates by generating new reward circuits that eventually restore normal motivation.」

    = 新たな報酬回路を作り動機を回復させる ━ 本文にそのような代償機構の記述はなく無関係なもっともらしい虚構。

  • 「The dopamine system shuts down almost entirely, leaving the user permanently unable to experience any form of motivation whatsoever.」

    = ドーパミン系が完全停止し動機を失う ━ 本文は系が乗っ取られ過敏化すると述べ、完全停止とは矛盾。

  • 「The prefrontal cortex grows more active in order to override the intensified cravings.」

    = 前頭前野が活発化し渇望を抑え込む ━ 本文は前頭前野が弱まると述べており逆の主張。

▦Collocation
パターン意味例
strengthen a pathway経路を強化するRepeated use strengthens craving pathways.
erode self-control自制を侵食するDrug use slowly erodes self-control.
drug-associated cue薬物関連の手がかりA drug-associated cue triggers craving.
govern restraint抑制を司るThe prefrontal cortex governs restraint.
tip the balance均衡を傾けるThe changes tip the balance toward relapse.
❝例文

  • Cues once neutral now provoke overwhelming urges.

    かつて中立だった手がかりが今や圧倒的な衝動を誘発する。

  • The capacity to resist is steadily undermined.

    抵抗する力は着実に蝕まれていく。

  • This asymmetry explains compulsive relapse.

    この非対称が強迫的な再発を説明する。

  • Wanting outlives any pleasure the drug once gave.

    渇望は薬がかつて与えた快楽より長く残る。

💡Tip · 覚えるコツ

「非対称な変化(一方が強化・他方が弱化)」を問う設問では、両側の方向を取り違えた逆転誤答が定番。動詞の極性(strengthen/erode, heighten/weaken)を必ずペアで確認し、どちらがどう動くかを図式化して照合する。

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