雅思阅读 164: The Almond-Shaped Alarm Inside Our Heads（头颅中的杏仁状警报器）

改编自 NeuroLaunch / Neuroscience of Affect（2026年5月）。雅思阅读 Section 3 难度，约 1050 词。 素材来源：https://neurolaunch.com/fight-or-flight-amygdala/

Reading Passage

A. Deep within each temporal lobe sits a small, almond-shaped cluster of neurons named, after the Greek word for its resemblance, the amygdala. For as long as humans have faced predators, falls and rival clans, this little nucleus has served as the brain's primary threat-detection system — and it works with a speed that modern neuroscience finds almost embarrassing. By the time a person consciously registers that something is wrong, the amygdala has often already acted. Neuroimaging studies show it begins firing roughly 30 to 80 milliseconds after a potentially dangerous stimulus appears, whereas the felt emotion of fear does not reach awareness until at least 150 to 300 milliseconds later. The delay exists because of what researchers call the "low road": a fast, rough sensory pathway that runs straight from the thalamus to the amygdala, bypassing the thoughtful cortex entirely. A slower, richer signal arrives by the "high road" a fraction of a second later. The low road trades accuracy for speed, which explains why people flinch at a coiled garden hose on a path before realising it is not a snake. In an environment where half a second of hesitation could be fatal, that mistake of over-caution was never a bug but the whole point of the design. The cost of a false alarm — a wasted flinch, a burst of adrenaline over a harmless shape — is trivial beside the cost of a single missed predator. Evolution therefore tuned the system to prefer a hundred unnecessary starts over one fatal delay.

B. The moment the amygdala classifies a signal as dangerous, it relays the verdict to the hypothalamus, which rouses the sympathetic nervous system and orders the adrenal glands to flood the bloodstream with epinephrine — adrenaline — together with cortisol. The resulting cascade, first described systematically by the physiologist Walter Cannon in 1932, was once labelled the "fight or flight" response, and it refashions the body within seconds. Heart rate climbs, sometimes doubling; blood pressure rises; breathing becomes rapid and shallow; digestion is put on hold; blood is diverted away from the gut and immune system toward skeletal muscle; pupils dilate to gather more light; and the liver releases stored sugar into the blood. The mouth goes dry, the shoulders and jaw tense, peripheral vision narrows into a tunnel and cold sweat prickles the skin. Internally, norepinephrine floods the gaps between nerve cells, sharpening alertness and narrowing attention onto the perceived threat. This whole-body shift, termed sympathetic arousal, is the deliberate opposite of the calmer "rest and digest" state governed by the parasympathetic branch, and the contrast between them explains why sustained emergency feels so exhausting.

C. The deeper trouble is that this ancient circuit cannot tell a charging lion from a hostile email. Neurologically, a looming predator and a quarterly performance review register as equivalent threats, and the body launches the same survival cascade for both. Traffic jams, critical messages on social media, financial worries and family quarrels do not, in any physical sense, require someone to sprint or throw a punch, yet the amygdala has not updated its classification since humans hunted on savannahs. Because the response is fast and blunt by design, it errs heavily on the side of caution — fire first, ask questions later — which was brilliant against predators and is increasingly costly in offices. The psychologist Daniel Goleman coined the phrase "amygdala hijack" for the moment when the emotional brain takes the controls before the rational brain can weigh in: the insult blurted out, the mind blanked mid-speech, the snap at a loved one after a hard day. Such episodes occur because a strong threat signal, especially in someone already primed by stress, overwhelms the slower, deliberative cortical circuits.

D. What once looked like a passing feeling, though, may leave a lasting mark. Sustained stress does not merely alter mood; it physically remodels the brain. Cortisol, the chief stress hormone, alters the architecture of neurons in three linked regions: the hippocampus, which consolidates memories and helps place threats in context; the amygdala itself; and the prefrontal cortex, the region responsible for rational appraisal and for putting the brakes on emotion. In the hippocampus, volume tends to fall. In the prefrontal cortex, connectivity weakens and tissue atrophies — precisely the brakes that are needed to calm a panicked response. The amygdala, paradoxically, can grow larger and become hyper-reactive, so that future alarms fire more easily. The prefrontal cortex, the region that should apply context and restraint, loses both volume and the number of connections through which it could calm the lower centres. These are not metaphors but differences visible on structural scans, and early-life adversity amplifies them: children raised in chronic stress show altered amygdala and hippocampal development that can echo into adulthood, a finding central to understanding conditions such as post-traumatic stress. The cruel detail is that the changes compound: an over-reactive amygdala triggers more alarms, which further stresses the brain, which makes the amygdala yet more sensitive.

E. The encouraging counterpoint is that these changes are not necessarily permanent. Neuroplasticity, the process by which brain circuits rewire themselves, runs in both directions, and the same cortisol-driven remodelling that causes harm can be partly reversed when stress subsides. Interventions that strengthen the prefrontal cortex and dampen the amygdala — regular aerobic exercise, adequate sleep, mindfulness training and psychotherapy — have been shown to recover some lost volume and reduce over-reactivity, provided they are sustained over months rather than days. The aim is not to eliminate the alarm itself, which is as vital as it is ancient, but to repair the mismatch between a circuit built for claws and teeth and a world filled with deadlines. Whether such rewiring can be delivered at population scale remains an open question, but the biology at least confirms that an overactive alarm, given the right conditions, can learn to quieten again.

Questions 1-4

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

List of Headings i. How the body is refashioned within seconds ii. The history of Greek medicine iii. An ancient circuit misfiring in modern life iv. The financial cost of workplace stress v. How stress physically remodels the brain vi. Why the amygdala resembles a snake vii. The possibility of rewiring an overactive alarm

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. Why does the amygdala react before conscious awareness? A. The cortex is physically disconnected from the senses. B. A fast "low road" passes sensory signals directly to it, bypassing the cortex. C. Consciousness develops only in adulthood. D. The amygdala is larger than the cortex.

6. What happens to the body during sympathetic arousal? A. Digestion and immune activity are temporarily suppressed. B. Blood flow shifts toward the stomach. C. Pupils constrict to protect the eyes. D. Heart rate gradually slows to rest levels.

7. What does the "amygdala hijack" describe? A. A surgical technique for removing the amygdala. B. The emotional brain acting before rational thought intervenes. C. A drug that blocks adrenaline receptors. D. The slowest pathway in the visual system.

8. How does chronic stress affect the prefrontal cortex? A. It enlarges it and sharpens reasoning. B. It weakens its connectivity and atrophies tissue. C. It has no measurable effect. D. It converts it into amygdala tissue.

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 amygdala typically begins firing before a person consciously feels fear.
10. Walter Cannon first described the fight-or-flight response in the 1930s.
11. The amygdala reacts more strongly to physical threats than to social threats.
12. Early-life adversity can alter brain structure in ways that persist into adulthood.
13. Mindfulness training has been shown to reverse all stress-related brain changes completely.

Questions 14-15

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

The amygdala reacts via a fast "low road" that bypasses the thoughtful (14) __________, trading accuracy for speed. Under chronic stress, the hippocampus loses volume while the amygdala can expand and become (15) __________.

答案与解析

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