Moment
The monkeys that lost their fear
The University of Chicago, laboratory of Heinrich Klüver and Paul Bucy, late 1930s
In the late 1930s, Heinrich Klüver and Paul Bucy removed large portions of the temporal lobes, including the amygdala, from rhesus monkeys at the University of Chicago. The animals underwent a dramatic personality change: previously wary monkeys became tame and unafraid, approaching snakes and people that would normally terrify them, along with other striking behavioral shifts. The cluster of changes became known as Klüver–Bucy syndrome.
- Chicago
- 1937–39
- Method
- Temporal-lobe removal
- Result
- Fearlessness
The caveat
The original lesions were large and imprecise, removing much more than the amygdala, so the early experiments implicated a whole region rather than isolating one structure. The specific role of the amygdala was pinned down by later, finer studies.
The experiment was among the first hard evidence linking a specific brain region to fear, and it pointed later researchers toward the amygdala as the critical structure. Decades of further work confirmed and refined the picture Klüver and Bucy had stumbled into: lesion studies, electrical stimulation, and eventually the human case of a patient known as S.M., who could feel almost no fear after amygdala damage.
The pattern of tameness, altered appetite, and loss of fear still carries both researchers' names as Klüver–Bucy syndrome.
How it connects
The experiment that first showed what the region does by removing it and watching fear disappear.
This moment appeared in The alarm that runs ahead of thought, the Involves connection for August 24, 2026, which asked: Why do you flinch before you know what scared you?
Check yourself
What did Klüver and Bucy observe after removing parts of monkeys' temporal lobes?
The animals lost normal fear and reacted calmly to things that had frightened them.. Right. The monkeys grew strangely tame and unafraid, early evidence that this brain region gates fear.
What the sources establish
Klüver and Bucy's temporal-lobe lesions in monkeys produced tameness and loss of fear, later termed Klüver–Bucy syndrome.
Sources
Amygdala (Encyclopaedia Britannica, 2024), Sections on the amygdala's role in fear and Klüver–Bucy syndrome