雅思阅读 105: Each Neuron Is a Neural Network

Adapted from 'Neuroscientists have vastly underestimated brain cells computing power', Scientific American, August 2026.

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One of the central mysteries of the brain is how it achieves so much with so little. At any moment, it processes an entire world of input, pilots a body and generates conscious experience, all with modest energy demands. Traditionally, the brains 86 billion neurons are each assumed to be a single processor. But researchers have now found direct evidence that a neuron houses many processors.

The study, published in Science, shows that neurons many branches, called dendrites, can compute information independently of the cell body. Senior author Attila Losonczy of the University of Texas Southwestern Medical Center says dendrites dramatically expand the computational capacity of individual neurons.

Textbook diagrams make neurons look deceptively simple, with only a handful of dendrites. In reality, they sprawl into elaborate treelike arbors, allowing one neuron to receive input from thousands of neighbors. Scientists once thought dendrites were boring cables that merely passed signals to the cell body for processing. Nature puts a lot of effort and energy into maintaining those branched structures, Losonczy says.

To test whether dendrites compute on their own, Losonczys team used voltage-imaging technology to record activity in individual neurons in mouse hippocampi while the mice ran on miniature wheels through virtual environments searching for rewards.

In familiar environments, dendrite activity generally matched the cell body. But when the researchers moved the reward within familiar surroundings, the cell body adjusted quickly while certain dendrites kept traces of earlier activity. In an entirely new environment, some dendrites changed activity to represent the new location before the cell body, which caught up only after repeated exploration.

This suggests dendrites compute information on their own. Their ability to preserve traces of the past or get ahead of the cell body raises the possibility that they serve as local memory devices. Perhaps the best analogy is that a neuron itself is already a neural network, says Antonio Fernandez-Ruiz of Cornell University.

Beverley Clark of University College London thinks independent dendrites make each neuron super flexible. It is what you see across the dendritic tree that is really important, she says.

Questions 1-5

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

1. How many neurons does the brain have? A. 86 million B. 86 billion C. 86 trillion D. 860,000
2. What are dendrites? A. The cell body B. Treelike branches of a neuron C. A type of neurotransmitter D. Brain scans
3. What did scientists previously think dendrites did? A. Computed independently B. Were merely cables passing signals C. Stored memories only D. Generated emotions
4. In new environments, what happened first? A. The cell body adjusted first B. Some dendrites changed activity before the cell body C. The mice stopped running D. Nothing changed
5. How does Fernandez-Ruiz describe a neuron? A. A simple switch B. Already a neural network C. A passive wire D. A muscle cell

Questions 6-10

Do the following statements agree with the information? Write TRUE, FALSE or NOT GIVEN.

6. The study was done on mice.
7. Dendrites can compute independently of the cell body.
8. Neurons in real life have only a few dendrites.
9. Dendrites may act as local memory devices.
10. The brain uses a huge amount of energy.

Questions 11-13

Complete the summary. Choose ONE WORD ONLY.

Dendrites are treelike 11 that receive input. In new environments, some dendrites represent the new 12 before the cell body. They may serve as local 13 devices.

Answers

1. B 2. B 3. B 4. B 5. B
2. TRUE 7. TRUE 8. FALSE 9. TRUE 10. FALSE
3. branches 12. location 13. memory

Key Vocabulary

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