Sechenov and Pavlov: the brain works by reflexes
A reflex is an automatic reply of the body to a signal. In 1863 the Russian scientist Ivan Sechenov wrote that even thoughts and feelings begin as reflexes in the brain. Later Ivan Pavlov tested this with careful experiments on dogs. He got a Nobel Prize in 1904 for his work on digestion, and then spent decades studying how animals learn.
Higher nervous activity means the work of the brain cortex (the thin outer layer of the brain) and nearby parts that controls learning, memory, speech, feelings and behaviour. The spinal cord alone cannot do this.
Inborn and conditioned reflexes
Unconditioned (inborn) reflex: you are born with it. Examples: saliva when food is in the mouth, pulling the hand from a hot pan, blinking, sucking in a baby. It is the same in all members of the species, it lasts for life and it uses the spinal cord or the lower brain.
Conditioned (learned) reflex: you build it during life. It differs from person to person, it can fade, and it needs the cortex.
| Inborn | Conditioned | |
|---|---|---|
| Origin | Born with it | Learned in life |
| Same in all? | Yes | No, it is personal |
| Lasts | All life | Can fade |
| Example | Saliva for food | Saliva for a bell |
How a conditioned reflex forms and fades
- Start with an inborn reflex: food gives saliva.
- Pick a neutral signal, such as a bell. By itself it gives no saliva.
- Give the bell just before the food, many times. The cortex makes a temporary link between the bell area and the food area.
- Now the bell alone gives saliva. The bell has become a conditioned signal.
Extinction: if the bell keeps ringing without food, the link weakens and the reflex stops. This is not forgetting. It is the brain learning a new rule, "the bell is no longer followed by food". The old link can come back quickly if food returns.
Rules: the signal must come first, and the pairing must repeat. A reward that matters (food, danger) makes the link form faster.
Speech, memory and emotions
Speech: a word can be a signal for a thing. Pavlov called words "the signal of signals". Only humans use language to think and plan. Speech areas are in the left side of the cortex in most people.
Memory keeps what we learn. Short-term memory holds a few items for seconds, like a phone number you just heard. Long-term memory stores things for years. Repeating and linking facts to meaning move them from short-term to long-term. Sleep also helps this.
Emotions are strong feelings such as joy, fear and anger. They are driven by deeper brain parts (such as the limbic system) with the cortex. They change the heartbeat, breathing and what we remember. Fear of a dog bite can become a conditioned reflex too.
Temperament
Temperament is your natural style of reacting: how fast, how strong, how steady. Pavlov linked it to how strong, balanced and mobile the nerve processes are. The old four types are:
- Sanguine: lively, quick, cheerful.
- Choleric: fast and strong, easily angry.
- Phlegmatic: calm, slow, steady.
- Melancholic: sensitive, careful, gets tired by strong stress.
Most people are a mix. No type is better. Character (habits and values) is built by life and can change; temperament changes much less.
Sleep
Sleep is not a switch-off. The brain stays busy. Two main kinds repeat every 90 minutes or so:
- Slow-wave (deep) sleep: the body rests, breathing slows and growth hormone is released.
- REM sleep: eyes move quickly, most vivid dreams happen, and the brain sorts memories.
Pavlov saw sleep as protective inhibition: nerve cells rest after hard work. School-age children need about 8 to 10 hours. Poor sleep lowers attention and memory. Tips: fixed bedtime, no phone screens for an hour before sleep, a dark and quiet room.
Try it: a conditioned signal at home
In the 3D scene press Bell + food four times, then press Ring bell alone. Predict first: will saliva flow? Then press Ring bell four more times with no food and watch the link bar fall.
At home: ask a friend to blow a whistle just before every snack time for a week. Notice what your own mouth does when you hear the whistle in week two. (Only if a friend agrees and the snacks are healthy.)
Key formulas and definitions
- Inborn reflex: stimulus โ spinal cord / lower brain โ response (same for all)
- Conditioned reflex = neutral signal + inborn stimulus, repeated (signal first) โ cortex link
- Extinction = conditioned signal repeated without reward โ link weakens
- Four temperaments: sanguine, choleric, phlegmatic, melancholic
- Sleep cycle โ 90 min: slow-wave sleep + REM sleep
Worked examples
1. A child jumps when a balloon pops, but a baby who has never seen balloons does not. Which reflex is this?
Hearing a loud bang can start an inborn startle reflex in everyone. If the child jumps because she has learned that balloons pop, that part is conditioned. So it is a mix: startle is inborn, fear of balloons is learned.
2. Put these in order to build a conditioned reflex: (a) bell alone gives saliva, (b) pair bell with food many times, (c) food gives saliva, (d) bell alone gives nothing.
Order: (c) โ (d) โ (b) โ (a). First the inborn reflex, then check that the bell is neutral, then pair them, then test the bell alone.
3. After the dog learned the bell reflex, the bell rings 10 times with no food. What happens and what is it called?
The saliva gets less each time and finally stops. This is extinction. The link is weak, but not erased, so the reflex can return fast if food is paired with the bell again.
Common mistakes
- Thinking all reflexes are inborn. Conditioned reflexes are learned.
- Putting the food before the bell. The signal must come first.
- Saying extinction means the dog forgot. It means the brain learned the bell no longer predicts food.
- Thinking temperament and character are the same. Temperament is natural style; character is built by life.