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Why is it hard to tickle yourself?

A touch you make yourself can feel different from a similar touch made by someone else. Experiments that delay the feedback from a person’s own movement probe a possible explanation: the nervous system predicts some of the sensations an action will cause.

4–6 min

Questions you could explore

  • Why would changing the timing of self-produced touch help test the prediction explanation?
  • What else would need to stay the same in that comparison?

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Health and the body

How does daylight set the body’s clock?

Feeling sleepy at night involves more than counting the hours since you woke up. Internal daily rhythms respond to outside cues, with light helping coordinate the body's sense of time.

3–5 min

How does daylight set the body’s clock?

Health and the body3–5 minFeeling sleepy at night involves more than counting the hours since you woke up. Internal daily rhythms respond to outside cues, with light helping coordinate the body's sense of time.

Health and the body

How does a vaccine give the immune system a memory?

The immune system can respond differently to something it has encountered before. Vaccines make use of recognition and memory, though different vaccine types introduce the relevant information in different ways.

4–5 min

How does a vaccine give the immune system a memory?

Health and the body4–5 minThe immune system can respond differently to something it has encountered before. Vaccines make use of recognition and memory, though different vaccine types introduce the relevant information in different ways.

Health and the body

Why won’t an antibiotic treat a viral cold?

The word infection covers illnesses caused by very different organisms. An antibiotic that helps against certain bacteria has no matching target in the viruses that cause a cold.

2–3 min

Why won’t an antibiotic treat a viral cold?

Health and the body2–3 minThe word infection covers illnesses caused by very different organisms. An antibiotic that helps against certain bacteria has no matching target in the viruses that cause a cold.

Why is it hard to tickle yourself? | Speech Topic | speaking.app