🎯 Objectives
These lessons would familiarize the students with:
- The stages of development of the brain 🧠 and the changes which takes place 🔄
- Various stages of neuronal development 🧬🔬
- Cell differentiation 🧫, determination, migration 🚶, cell competition ⚔️, cell death 💀
- Teratogenesis 🧬⚠️ - Genetic anomalies which affect development of the brain 🧠
- Plasticity of the Nervous system 🔄💪
🌍 Additional Influences on Brain Development
💨 Oxygen Level
Oxygen is very important for the brain cells 🧠 during growth 🌱 as well as throughout life 💫. As the embryo depends on the mother 🤰 for its oxygen supply 💨, any reduction in the normal level ⬇️ would affect the growing brain 🧠⚠️. If the mother is not getting enough oxygen ❌💨 during last trimester 📅, this leads to hypoxia 💨⚠️ (low oxygen levels) of the fetus 👶. If the mother's blood circulation is faulty 🩸⚠️, then it would lead to damage of the brain areas 🧠💔 which may have developed normally 😞 (anemia 🩸⬇️, and heart disorders 💔 in mothers leads to this problem ⚠️). This damage is similar to that of mental retardation 🧠⚠️. Why? Because neurons die off 💀 and lesser number of cells remains 🧫⬇️ leading to deficient functioning of these areas 🎯❌.
💪 Prenatal Motor Activity
This is important as there is evidence if their increased activity in uterus 🤰🏃 this leads to stronger muscles 💪✨. This is exercising muscular connection 🔗, and their pathways 🛤️. Thus, motor connections are strengthened even within utero 🤰💪. Not just motor exercises 🏋️, but sensory responses are also there 👂👁️. Evidence has shown that the embryo/fetus responds to mother's lullabies 🎵 and voice 🗣️. Those fetuses which are stimulated during the prenatal period ⏰📡 are more alert 👀 when they are born 🍼.
💊 Drugs: Teratogenic Effects
Though the placental barrier protects the embryo 🛡️👶, there are some substances which manage to pass through the protective membranes 🧬⚠️. It was discovered in the 1960's 📅 that drugs affect the normal growth of the fetus 💊⚠️, leading to serious deformities 😢. Thalidomide was the first drug to have been identified to have teratogenic effects 💊☠️. This sedative 😴💊 was given to expecting mothers 🤰 in the 1st three months 📅; it caused major deformities 🦾⚠️ in the growing embryo 👶. Similarly, morphine 💉, heroin 💉, alcohol 🍷, nicotine 🚬, cocaine 💊 and tobacco 🚬 also affect the embryo 👶⚠️. Mothers are warned against taking these or other pharmaceutical substances during pregnancy ⚠️🤰 - teratogenic effects ☠️.
📡 External Stimulation
This is very important for the growing embryo 👶. Unless external stimulation is received 📡✅ the organs and muscles do not develop normally 💪❌. Therefore, sensory deprivation leads to irreversible defects ❌💔 in normal growth of the brain 🧠.
👁️ Hubel and Wiesel's Classic Experiments (1963)
In the now classic experiments 🔬, Hubel and Wiesel closed one eye 👁️✂️ in newborn kitten 🐱 creating monocular deprivation 👁️❌. They found monocular response to visual stimuli 👀 (only one eye could respond 👁️✅ even though the visual system was not damaged ✅). In another experiment, kittens were kept in dark room 🕶️🌑 from birth onwards 📅; it was found that:
- Visual pathways atrophy 👁️💀
- Visual cortical brain areas also degenerate 🧠⬇️
- Irreversible damage causing blindness 🙈❌
Thus, early sensorimotor stimulation 📡💪 is important for the brain to grow normally 🧠✅. To stimulate the brain 🧠 now some mobile 🎨 and brightly colored toys 🧸 are placed in the cots 🛏️ for the newborn to see 👶👀.
🎨 Complex Environment
Rozenzweig et al (1969, 1972) raised rats 🐀 in an enriched environment 🎨✨ (more toys 🧸, swings 🎠, ladders 🪜, etc.). They took out the brains 🧠 and measured various parts of the brain 📏. They report:
- a) Increased brain weight 🧠⚖️⬆️ (especially cerebral cortex 🧠)
- b) Increased thickness of cortical tissue 📏⬆️
- c) Larger size of neurons 🧫⬆️
- d) More glial cells 🔬⬆️
- e) More dendritic spines 🌿⬆️
- f) Chemistry of brain also different 🧪 (enzyme activity ⚗️)
Greenough (1975) and colleagues also report that rats raised in a complex environment 🎨:
- a) Had increased dendritic sprouting 🌿📈
- b) Responded to novel environment 🌍 in same way as mildly stressed rats 😰✅
⏰ Critical Periods
External stimulation environment extremely important 🌍✅ – but only during the periods in which it is needed to be present in the system ⏰. Beyond that neither effect ❌ nor repair ❌ is possible.
📚 References
- Kalat, J.W. (1998). Biological Psychology. Brooks/Cole Publishing Company.
- Carlson, N. R. (2005). Foundations of physiological psychology. Pearson Education New Zealand.
- Pinel, J. P. (2003). Biopsychology. (5th ed). Allyn & Bacon Singapore.
- Bloom, F., Nelson., & Lazerson. (2001), Behavioral Neuroscience: Brain, Mind and Behaviors. (3rd ed). Worth Publishers New York
- Bridgeman, B. (1988). The Biology of Behavior and Mind. John Wiley & Sons, New York
- Brown, T.S. & Wallace, P.S. (1980). Physiological Psychology. Academic Press, New York